b o r d e n i n s t i t u t e m o n o g r a p h s e r i e s

Load Carriage in

Military Operations

Joseph Knapik, ScD, and Katy Reynolds, MD

e d i t e d b y

William R. Santee, PhD 

Karl E. Friedl, PhD, Colonel, US Army

A REVIEW OF HISTORICAL, PHYSIOLOGICAL,

BIOMECHANICAL, AND MEDICAL ASPECTS

b o r d e n i n s t i t u t e m o n o g r a p h s e r i e s

borden institute

Load Carriage 

in Military

Operations

A Review OF HISTORICAL, PHYSIOLOGICAL, 

BIOMECHANICAL, AND MEDICAL ASPECTS

Joseph Knapik, ScD, and Katy Reynolds, MD

e d i t e d b y

William R. Santee, PhD

Karl E. Friedl, PhD, Colonel, US Army
Making loads lighter, improving load distribution, using appropriate physical training, 

selecting proper equipment, and choosing specific techniques directed at injury 

prevention will all facilitate load carriage. Suitable changes will allow service members 

to continue missions at lower energy costs and with fewer injuries, and be better able 

to perform other tasks.

This monograph was prepared for military medical educational use. The focus of the information is to foster discussion that may form the basis of doctrine and policy. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.

Dosage Selection: The authors and publisher have made every effort to ensure the accuracy of 

dosages cited herein. However, it is the responsibility of every practitioner to consult appropriate information sources to ascertain correct dosages for each clinical situation, especially for 

new or unfamiliar drugs and procedures. The authors, editors, publisher, and the Department 

of Defense cannot be held responsible for any errors found in this book.

Use of Trade or Brand Names: Use of trade or brand names in this publication is for illustrative 

purposes only and does not imply endorsement by the Department of Defense.

Neutral Language: Unless this publication states otherwise, masculine nouns and pronouns do 

not refer exclusively to men.

Certain parts of this publication pertain to copyright restrictions. 

ALL RIGHTS RESERVED.

No copyrighted parts of this publication may be reproduced or transmitted in any form 

or by any means, electronic or mechanical (including photocopy, recording, or any information storage and retrieval system), without permission in writing from the publisher or 

copyright owner.

Borden Institute

Walter Reed Army Medical Center

US Army Medical Department Center & School

This monograph was originally submitted to the Borden Institute as a chapter intended for 

publication in Military Quantitative Physiology, a book in the Textbooks of Military Medicine 

series. Because changes may be made before publication, this monograph is made available 

with the understanding that it will not be cited or reproduced without the permission of the 

publisher.
CONTENTS

Foreword v

Acknowledgments vii

Introduction 1

Historical Perspective 5

Loads Carried During Various Historical Periods 5

19th- and 20th-Century Efforts to Study Load Carriage 5

Load Carriage Throughout History 12

Body Stature and Body Mass as Factors in Load Carriage 14

Physiological and Biomechanical Aspects of Load Carriage 15

Load Distribution 15

Backpacks and Double Packs 20

Load Carriage on the Feet, Thighs, and in the Hands 24

Rifle Carriage 25

Body Armor 25

Load Carriage Using Carts and Motorized Vehicles 27

Physiological Factors Associated With Load Carriage 28

Physical Training and Load Carriage 29

Gender Differences 31

Predicting the Energy Cost of Carrying Military Loads 31
Medical Problems Associated With Load Carriage 35

Foot Blisters 35

Metatarsalgia 43

Stress Fractures 43

Knee Pain 45

Low Back Injuries 46

Rucksack Palsy 47

Meralgia Paresthetica 48

Influence of Load Carriage on the Performance of Other Tasks 49

Summary 51

References 53

Cover photo: Courtesy of US Air Force, TSgt Efren Lopez, photographer

Joseph Knapik is a Major (Ret), Medical Service Corps, US Army; Research Physiologist, Injury Prevention Program, US Army Public Health Command (Provisional), 5158 Blackhawk 

Road, Aberdeen Proving Ground, Maryland 21005-5425.

Katy Reynolds is a Colonel (Ret), Medical Corps, US Army; 8820 Burning Tree Road, Pensacola, Florida 32514.
Foreword

This monograph presents a comprehensive overview of research on 

soldier load carriage. The authors demonstrate broad personal research 

and reporting experience from both field and laboratory perspectives. 

This knowledge helps provide an implicit framework for categorizing and 

evaluating past research, as well as for planning future research efforts. 

Loads carried by soldiers have been of scientific concern since around 

the 18th century and is a continuing problem, as recognized by soldiers 

operating in rugged terrain in Afghanistan today. It is perhaps shocking 

that, with technological advances, the problems have worsened rather 

than improved. Improvements in weaponry, surveillance, communications, and personal protective equipment have added to the soldier load, 

and this has only partially been compensated by enhanced strategies to 

safely and effectively manage those loads. The problem of load carriage 

has been reviewed by a number of military committees and organizations 

that have provided suggestions for reducing the stress of loads. Generally, 

these groups were tasked with narrowly focusing on a particular, thentimely perspective; findings were directly applicable to the issues directly 

at hand, but were not always of strategic value appropriate to broader 

scientific concerns. Thus, to some degree, developed knowledge based 

on load carriage has not been fully explored. Missing, to a large extent, 

is research on the relationship between the known state of load carriage 

comfort, energy cost, and ergonomic “fit,” and the ongoing introduction of ancillary technologies (eg, robotics, automation, and real-time 
communications devices), as well as vision and hearing enhancements. 

This monograph provides a concrete, data-based framework needed 

to guide the introduction of such evolving topics into the load carriage 

research arena.

The section on physiology and biomechanics provides an overview of 

current load carriage systems and highlights information on load placement, pack frames, hip belts, and strap adjustments. Although materiel 

and combat developers have considered some information noted herein, 

other research is relatively new or has not been adequately promulgated 

to these developers. A stark example of potential improvements is taken 

from gains in female load carriage performance and comfort, once load 

carriage equipment was finally updated in the past decade to accommodate smaller framed women with different anthropometric dimensions 

than the average male. 

Another section reviews the equations that quantify the impact of 

load distribution on the mechanics and energy cost of load carriage. This 

detailed contribution to the knowledge base permits the exploration of 

new technologies, such as virtual prototyping of new systems, to produce 

safer and more effective load carriage than ever before. The literature on 

rifle carriage and body armor is covered, as well as alternative methods 

of load carriage (eg, carts and motorized vehicles). Unfortunately, it is 

still necessary to discuss injuries associated with load carriage, and this 

monograph provides practical information on the signs and symptoms 

of these injuries, as well as treatment and evidence-based suggestions 

for injury prevention. 

The authors worked for many years at the US Army Research Institute of Environmental Medicine (USARIEM), where much of the US

research on load carriage has been conducted. They have gained broader 

perspectives serving with organizations such as the US Army Research 

Laboratory and the US Army Center for Health Promotion and Preventive Medicine (now the US Army Public Health Command).

Karl E. Friedl, PhD, Colonel, US Army

 Director, Telemedicine and Advanced Technology 

Research Center 

 US Army Medical Research and Materiel Command

 Rene de Pontbriand, PhD

Associate Director for Science and Technology (Ret)

Human Research and Engineering Directorate

 US Army Research Laboratory

vi | Foreword
Acknowledgments

The authors thank Major James Nagel, Mr William Harper, and Dr 

Rene de Pontbriand for their helpful comments. Colonel Karl Friedl, Dr 

William Santee, and Mr Ryan Steelman assisted with many of the photos 

and in bringing this monograph to fruition.

Introduction 

Because of mission requirements or the limited transportation assets of 

some types of units, service members must often depend on their personal 

mobility to move individual equipment. The carrying of loads by troops 

is an important aspect of military operations that can become critical in 

some situations. Overloading with ammunition and equipment can lead 

to excessive fatigue and impair the ability to fight. Military historians 

can cite numerous examples when heavy loads directly or indirectly 

resulted in reduced performance, unnecessary deaths, and lost battles 

(Exhibit 1).1–4 The experience of British troops in the Falkland Islands 

War (1982) and US Army troops in both Grenada (1983) and Afghanistan (1999–2010) emphasizes that overloading troops is still a problem 

in modern warfare.5–7

The purpose of this monograph is to review the historical, physiological, biomechanical, and medical aspects of load carriage. Practical 

suggestions are offered for reducing the stress of loads on service members 

and for preventing and treating common load carriage-related injuries. 

Reviews on other aspects of load carriage are available in the works of 

Haisman8 and Knapik et al.9,10
Exhibit 1. Heavy Loads in Military History

Omaha Beach, France (1944)(1)

“In the initial assault waves at Omaha Beachhead there were companies whose 

men started ashore, each with four cartons of cigarettes in his pack—as if the 

object of the operation was trading with the French. Some never made the shore 

because of the cigarettes. They dropped into deep holes during the wade-in, or fell 

into the tide nicked by a bullet. Then they soaked up so much weight they could 

not rise again. They drowned. Some were carried out to sea but the great number 

were cast up on the beach. It impressed the survivors unforgettably—that line of 

dead men along the sand, many of whom had received but trifling wounds. . . . 

No one can say with authority whether more men died directly from enemy fire 

than perished because of the excess weight that made them easy victims of the 

water. . . . This almost cost us the beachhead. Since it is the same kind of mistake 

that armies and their commanders have been making for centuries, there is every 

reason to believe it will happen again.” 

Grenada (1986)(2)

“Unfortunately too few commanders enforced load discipline. Consider this soldier’s observation: ‘We attacked to secure the airhead. We were like slow moving 

turtles. My rucksack weighed 120 pounds. I would get up and rush for 10 yards, 

throw myself down and couldn’t get up. I’d rest for 10 or 15 minutes, struggle 

to get up, go 10 more yards, and collapse. After a few rushes, I was physically 

unable to move and I am in great shape. Finally, after I got to the assembly area, 

I shucked my rucksack and was able to fight, but I was totally drained.’ Consider 

another soldier’s telling comment: ‘I was scared I was going to get killed because 

I couldn’t really run with that rucksack on.’ Even allowing for some exaggeration 

by the soldiers, no one can doubt they were overloaded.”

Saudi Arabia and Iraq (1990)(3)

“During Operation Desert Shield, a brigade conducted a live fire training assault 

to seize a bridge. The brigade commander noticed that the equipment the soldiers 

were carrying was interfering with the mission. At the after action review he directed 

the battalion commanders to investigate the weight the soldiers carried in their 

battalions. At the brief back one commander indicated that the average soldier in 

his battalion carried more than 100 pounds.

At Christmas 1990 the [2d Brigade, 82d Airborne Division] was conducting training far to the South of the front. During this relatively peaceful time, and especially 

as a result of the holiday, the soldiers had accumulated many items they could 

not take into combat. When the order came for the brigade to spearhead the 

French 6th Light Armored Division’s attack into Iraq, the chain of command took 

(Exhibit 1 continues)

2 | Load Carriage in Military Operations
steps to care for the soldier’s personal effects and excess baggage. They made 

a list of what a soldier would carry on his person (fighting load), what he would 

carry in his rucksack (approach march load), what he would carry in his A-bag 

(sustainment load), and what would go in his B-bag (contingency load). Items that 

did not fit in these categories, the soldier shipped home. . . . The battalions that 

entered the Euphrates River Valley had learned a valuable lesson as a result of 

their earlier training attack on the bridge. Although their fighting and approach 

march loads were still heavy, they knew better how to manage them. When units 

arrived at their landing zones, the battalions secured their rucksacks (approach 

march load) with a minimum guard force while the rest of the soldiers occupied 

their positions. As soon as practicable, soldiers went back, a few at a time, to 

retrieve the rucksacks. In at least one instance, a unit placed excess ammunition 

and water in kick-out bundles that could then be taken forward and stored in a 

central location for further distribution.” 

Afghanistan (2002)(4)

“We had extreme difficulty moving with all of our weight. If our movement would 

have been to relieve a unit in contact or a time sensitive mission we would not 

have been able to move in a timely manner. It took us 8 hours to move 5 clicks. 

With just the vest [Interceptor hard body armor] and LBV [Enhanced Tactical Load 

Bearing Vest or the MOLLE vest] we were easily carrying 80 lbs. Throw on the 

ruck and you’re sucking.” 

Data sources: (1) Marshall SLA. The Soldier’s Load and the Mobility of a Nation. Quantico, Va: Marine Corps 

Association; 1950. (2) Dubik JM, Fullerton TD. Soldier overloading in Grenada. Mil Rev. 1987;67:38–47.

(3) Porter SC. The soldier’s load. Infantry. 1992;May–June:19–22. (4) Comments from the 187th Regiment 

First Sergeant, Operation Anaconda.

Exhibit 1 continued

Introduction | 3

Historical Perspective

Loads Carried During Various Historical Periods 

Figure 1 shows loads that were carried by various military units in history, 

with emphasis on more recent times. Lothian11 provided data on ancient 

military units. Until about the 18th century, troops carried loads that seldom exceeded 15 kg as they marched. Extra equipment was often moved by 

auxiliary transport, including assistants, horses, carts, and camp followers. 

The extra equipment often consisted of weapons and protection used by 

troops when they went into battle (eg, swords and shields). After the 18th 

century, auxiliary transport was deemphasized, and more disciplined armies 

required troops to carry their own loads. The latter-day service member 

often carried more equipment during the march and less when in contact 

with hostile forces.2 It should be noted that most of the loads provided in 

Figure 1 are from estimates and literary sources. The only actually measured 

values are those from the Joint Readiness Training Center (in Fort Chaffe, 

Ark) and Operation Enduring Freedom (Afghanistan).

19th- and 20th-Century Efforts to Study Load Carriage

European Efforts 

After the Crimean War, a British “Committee Appointed to Inquire 

into the Effects of the Present System of Carrying Accouterments, Ammunition and Kit of the Infantry Soldier” recommended that soldier 
Figure 1. Loads carried on the march by various infantry units throughout history. Inf: infantry; JRTC: Joint Readiness Training Center (Ft Chaffee, Ark); OEF: 

Operation Enduring Freedom; US: United States; WWI: World War I; WWII: World War II. Data sources: Dean CE. The Modern Warrior’s Combat Load. Dismounted Operations in Afghanistan April–May 2003. Ft Leavenworth, Kan: Army Center for Lessons Learned; 2004. Downs F. The Killing Zone: My Life in the Vietnam War. New York, NY: Berkley Publishing Group; 1978. Holmes R. Acts of War. The Behavior of Men in Battle. New York, NY: MacMillan and Co, 1985. Joint Readiness Training Center. Unpublished data collected on units participating in exercises at the Joint Readiness Training Center, 1988. Lothian NV. The load carried by the soldier. J R Army Med Corps. 1922;38:9–24. Porter SC. The soldier’s load. Infantry. 1992;May–June:19–22. 

6 | LoadCarriage inMilitaryOperations

5040302010

0

Estimated Load Mass (kg)

Greek

Hoplites

Roman

Legions

Byzantine

Infantry

Anglo

Saxon

Freemen

English

Pikemen

Napoleonic

Wars

US

Civil

War

British

Crimean

War

JRTC

US

Vietnam

British

on 

Somme

WWI

US

Marines

Korea

US Inf

Desert

Shield

Wingate's

Chindits

WWII

Estimated load masses carried on the marchEstimated total mass of all equipment soldiers took OEF
loads be reduced to 21 kg through the elimination of “necessaries,” 

especially underclothing.2,4 Studies at the Frederick Wilhelm Institute 

in 1895 showed that, if the weather was cool, soldiers could tolerate 

marching 24 km with a load mass of 22 kg. In warm weather, this test 

caused “minor disturbances,” from which the men recovered in 1 day.2

In 1908, a “Committee on the Physiological Effects of Food, Training, 

and Clothing of the Soldier” developed a much-improved load carriage 

system that was used in World War I. In 1920, the Hygiene Advisory 

Board of the British Army recommended that the soldier’s load should 

not exceed 18 to 20 kg or one third of his body weight while marching. 

With the development of indirect calorimetry, Cathcart and colleagues12

were able to study the energy cost of two men marching at a variety of 

paces and with a variety of load masses. They found that energy cost 

per mass carried was lowest when subjects carried a mass equal to 40% 

of their body mass.

American Efforts

There is little information about American efforts to study load carriage formally before World War II, if these efforts even existed. Under 

the direction of the Quartermaster General, Captain H. W. Taylor developed a soldier “payload plan.” This was an attempt to unburden the 

soldier by providing him with only the items needed for combat. There 

were also attempts to develop segmented packs: if the tactical situation 

permitted, a portion of the pack containing nonessential equipment 

could be left behind.13

World War II led to many situations in which soldiers had to carry 

loads for long distances. Figure 2 shows American soldiers marching 

to relieve troops in the Ardennes Forest during the Battle of the Bulge. 

Figure 3 shows a training exercise in which a modern airman is being 

transported using a two-man carry, not an uncommon situation in World 

War II. Figure 4 shows an infantryman transporting loads by mules in 

Burma. Presumably drawing on many of the experiences from World War 

II, US Army Field Board No. 3 (Fort Benning, Ga) performed a number 

of studies from 1948 to 1950. Board members noted that previous work 

had ignored the individual soldier’s mission within the military unit. In 

studying individual positions, they found that loads ranged from 25 kg 

for the rifleman to 50 kg for the ammunition carrier. In cooperation 

with the Office of The Surgeon General, the Board estimated how load 

masses should be reduced to make the soldier more combat effective. 

Metabolic data and stress placed on soldiers in combat were considHistorical Perspective | 7
ered. Based on a literature review, the Board determined that the energy 

available for marching (with the basal metabolic rate subtracted) could 

not exceed 3,680 kcal/day. They recommended that a rifleman carry 18 

kg in the worst conditions; 25 kg was recommended as the maximum 

march load.14

About a decade later, the US Army Infantry Combat Developments 

Agency15,16 reinforced the weight recommendations of US Army Field 

Board No. 3. The agency recommended a load of 18 kg (or 30% body 

weight) for a conditioned fighting soldier and 25 kg (or 45% body weight) 

for a marching soldier. They developed the idea of “load echeloning” 

and defined a fighting load and an existence load. 

In 1987, the US Army Development and Employment Agency 

(ADEA; Fort Lewis, Wa) further developed the concept of load echeloning.17 They called the load carried by a soldier the combat load, defined 

as the mission-essential equipment required by soldiers to fight, survive, 

Figure 2. American soldiers marching to relieve troops encircled in the Ardennes Forest during 

the Battle of the Bulge.

Photograph: Courtesy of Olive-Drab.com. From http://www.olive-drab.com/od_history_

ww2_ops_battles_1944bulge.php.

8 | Load Carriage in Military Operations
Figure 3. An airman being transported using a two-man carry in a training exercise. 

Photograph: Courtesy of the US Air Force. From http://www.af.mil/shared/media/photodb/

photos/070515-F-4127S-706.jpg. 

Figure 4. Mars Task Force mule skinners (2nd Battalion, 475th Infantry Regiment) lead mules 

through the swift river that impeded their progress to Bhamo, Burma, November 17, 1944.

Photograph: Courtesy of Olive-Drab.com. From http://www.olive-drab.com/od_army-horsesmules_ww2.php. 

Historical Perspective | 9
and complete their combat mission. The combat load was further divided 

into a fighting load and an approach march load. The fighting load was 

carried when enemy contact was expected or stealth was necessary. 

It consisted of the soldier’s clothing, load-bearing equipment, helmet, 

weapon, rations, bayonet, and ammunition. The approach march load 

was carried in more prolonged operations. It included the combat load 

plus a pack, sleeping roll, extra clothing, extra rations, and extra ammunition. Current US Army doctrine recommends 22 kg (or 30% body 

weight) for the fighting load and 33 kg (or 45% body weight) for the 

approach march load.18

ADEA studied nine light infantry jobs that soldiers might have to 

perform in a worst-case situation. The loads carried by soldiers in these 

positions are shown in Table 1. ADEA17 proposed five approaches for 

lightening soldier loads: (1) development of lighter weight components—

however, technical developments were expected to reduce loads by only 

6% overall (see Table 1);19 (2) use of the soldier load-planning model—a 

computer program that aided the commander in tailoring loads through 

a risk analysis based on the mission, enemy, terrain, troops, and time; 

(3) development of specialized, load-carrying equipment (including items 

such as handcarts and all-terrain vehicles); (4) reevaluation of current 

doctrine that might affect load carriage (eg, an increased emphasis on 

marksmanship to reduce ammunition loads); and (5) development of 

special physical training programs to condition soldiers to develop more 

physical capability for load carriage.

Table 1. Worst Case Loads and Projected Weights Because of New Technologies (Including 

Clothing and Personal Equipment) for Nine US Army Light Infantry Positions

US Army Development and Employment Expected Weights Because of

Position Agency Worst-Case Loads (kg) New Technologies (kg)19

Assistant Dragon Gunner 76 74

Assistant Machine Gunner 69 59

Radio Telephone Operator 68 64

Dragon Gunner 64 61

Rifleman 62 64

Squad Automatic Weapon 59 57

Gunner

Platoon Leader 58 54

Machine Gunner 58 53

Grenadier 56 53

10 | Load Carriage in Military Operations
The first study of loads actually carried in combat was performed 

with a light infantry brigade (the 82nd Airborne Division) engaged in a 

low-intensity conflict in the deserts and mountains of Afghanistan during 

spring 2003. A team of infantrymen was dedicated to the data collection 

effort and also served to augment the combat forces. Loads were inventoried and weighed with digital scales on 15 separate occasions involving 

seven combat missions from April 4, 2003 to May 5, 2003. The loads 

carried by soldiers in each of the 29 duty positions are shown in Table 2. 

Table 2. Average Loads Carried by Light Infantry Soldiers During Dismounted Operations 

in Afghanistan in April and May 20035

Fighting Approach March Emergency Approach

Duty Position Load (kg) Load (kg) March Load (kg)

Rifleman 29 43 58

M203 Grenadier 32 48 62

Automatic Rifleman 36 50 64

Antitank Specialist 31 45 59

Rifle Team Leader 29 43 59

Rifle Squad Leader 28 43 58

Forward Observer 26 41 58

Forward Observer Radio/Telephone Operator 27 39 54

Weapons Squad Leader 28 45 60

M240 Machine Gunner 37 51 60

M240B Assistant Gunner 32 55 67

M240B Ammunition Bearer 31 53 65

Rifle Platoon Sergeant 28 41 54

Rifle Platoon Leader 28 42 53

Platoon Medic 25 42 54

Radio/Telephone Operator 29 45 No data

Mortar Section Leader 26 50 68

Mortar Squad Leader 28 58 65

60-mm Mortar Gunner 29 49 61

60-mm Mortar Assistant Gunner 25 55 No data

60-mm Mortar Ammunition Bearer 24 46 No data

Rifle Company Communication Chief 31 50 No data

Fire Support Officer 25 42 No data

Fire Support Noncommissioned Officer 24 41 65

Sapper Engineer 27 43 60

Company Executive Officer 27 42 No data

Company First Sergeant 29 41 57

Company Radio/Telephone Operator 29 44 59

Rifle Company Commander 30 44 50

Average 29 46 60

Historical Perspective | 11
The emergency approach march load was defined as the load that was 

carried in foot operations when the terrain was “impassable to vehicles 

or where ground/air transportation resources are not available.” It was 

noted that recent improvements in ballistic protection (interceptor body 

armor, advanced combat helmet) had increased soldier survivability, but 

had decreased mobility and endurance. Body armor and the protective 

helmet accounted for roughly 31% of the fighting load.5

Load Carriage Throughout History

Many of the approaches proposed more recently for reducing soldier 

loads5,17 are not new. For example, commanders and individual soldiers 

have practiced load tailoring throughout history. Iphicrates of Ancient 

Greece armed his infantry with only a wooden shield, lance, and sword. 

They defeated a Spartan force of heavily equipped Hoplites, presumably 

because of their greater agility. The Hoplites carried a load of about 37 kg 

into battle. In the 17th century, Gustavus Adolphus of Sweden lightened 

his soldiers’ loads by removing armor and shortening weapons. In the 

Boer Wars, the British Army carried only arms, ammunition, water, and a 

haversack—a total weight of 11 kg.2 Soldiers in battle have often reduced 

loads on their own initiative. During the highly successful Shenandoah 

campaign, the Confederate troops under Stonewall Jackson discarded 

extra clothing, overcoats, and knapsacks. They carried only rifles, ammunition, food, a blanket (or rubber sheet), and the clothing they wore.2,3 

American paratroopers entering Normandy in 1944 exited the aircraft 

with a load of about 36 kg. However, once on the ground, they quickly 

discarded equipment they considered unnecessary.3

A wide variety of load-carrying systems have also been used throughout history. The Greek Hoplites used helots (serfs in ancient Sparta) 

to carry their equipment on the march. Carts and packs were used by 

Roman legions. Oliver Cromwell’s armies used “pack boys.” Napoleon 

used carts whenever possible to relieve his soldiers of their march loads. 

Camp followers also carried much of the soldiers’ load during various 

wars.1,2

Physical training has been used to improve marching with loads. Roman legionnaires are estimated to have performed road marching three 

times per month at a rate of about 5 km/h carrying a 20-kg pack over a 

32-km distance. In Cromwell’s army (circa 1640), pay was contingent 

on marching 24 km on a regular basis. During World War I, the French 

12 | Load Carriage in Military Operations
Chasseurs (infantry), carrying a “light kit,” marched more than 13 to 18 

km two times per week. Recruit training in Germany during World War 

I included taking an initial 10-km march, with 1 km added weekly until 

recruits were marching 20 km with a “full kit.”2 McMichael20 gives a 

brief description of the training of Wingate’s Chindits (from the Burmese 

Table 3. Physical Characteristics of Soldiers and Recruits

 Body Mass Fat-Free Body 

Sample Height (cm) Weight (kg) Index (kg/m2) Mass (kg) Fat (%)

French Samples

French (Crimean War)2 163 56 21.1 NA NA

French (Post-WWI)

2 163 NA NA NA NA

British Samples

British (Post-WWI)

2 168 59 20.9 NA NA

British recruits (1978)(1) 175 70 22.9 NA NA

British infantry (1976)(1) 175 73 23.8 NA NA

US Samples

US male soldiers (1864)(2) 171 64 21.9 53* 16.9*

US male soldiers (1919)(2) 172 66 22.3 55* 15.7*

US male soldiers (1946)(2) 174 70 23.1 60* 14.4*

US male soldiers (1976)(3) 175 73 23.8 59† 19.5†

US male soldiers (1984)(2) 174 76 25.1 63‡ 17.3‡

US male soldiers (1986)21 177 76 24.2 NA NA

US male soldiers (1988)130 176 76 24.5 63* 15.9*

US male soldiers (1989)23 178 77 24.4 64‡ 15.9‡

US male soldiers (2004)§ 177 81 25.7 NA NA

US male soldiers (2005)(4) 178 83 26.4 68¥ 17.7¥

*Estimated from circumference measures.(5)

†Estimated from skinfolds.(6)

‡Estimated from densiometry.(7)

§Previously unpublished data, Fort Campbell, Kentucky. 

¥Estimated from dual X-ray absorptiometry.(8)

NA: not available; WWI: World War I

Data sources: (1) Vogel JA, Crowdy JP. Aerobic fitness and body fat of young British males entering the Army. Eur J Appl 

Physiol. 1978;40:73–83. (2) Friedl KE. Body composition and military performance: origins of the Army standards. In: 

Marriott BM, Grumstrup-Scott J, eds. Body Composition and Military Performance. Washington, DC: National Academy 

Press; 1992. (3) Vogel JA, Patton JF, Mello RP, Daniels WL. An analysis of aerobic capacity in a large United States 

population. J Appl Physiol. 1986;60:494–500. (4) Sharp M, Knapik JJ, Walker LM, et al. Changes in physical fitness 

and body composition following 9 months deployment to Afghanistan. Med Sci Sports Exerc. 2008;40:1687–1692. 

(5) Vogel JA, Kirkpatrick JW, Fitzgerald PI, Hodgdon JA, Harman EA. Derivation of Anthropometry Based Body Fat 

Equations for the Army’s Weight Control Program. Natick, Mass: US Army Research Institute of Environmental Medicine; 

1988. Technical Report 17-88. (6) Durnin JV, Womersley J. Body fat assessed from total body density and its estimate 

from skinfold thickness: measurements on 481 men and women aged 16 to 72 years. Br J Nutr. 1974;32:77–97. (7) 

Fitzgerald PI, Vogel JA, Miletti J, Foster JM. An Improved Portable Hydrostatic Weighing System for Body Composition. 

Natick, Mass: US Army Research Institute of Environmental Medicine; 1988. Technical Report T4/88. (8) Lohman TG. 

Dual energy X-ray absorptiometry. In: Roche AF, Heymsfield SB, Lohman TG, eds. Human Body Composition. Champaign, Ill: Human Kinetics; 1996.

Historical Perspective | 13
word “chinthe” [or lions]—also known as “Wingate’s Raiders”), who 

fought as light infantry during the Central Burma campaign in World 

War II. “They were loaded with huge 34-kg packs and marched unmercifully through man-killing terrain.”20 These soldiers performed a 225-km 

road march just before their deployment to Burma. Units within the US

Army’s 10th Mountain Division routinely road marched with their fighting loads about three times per month. Training guidance prescribed a 

quarterly road march of 40 km (7 min/km [or 11 min/mile] pace) and a 

yearly road march of 161 km in 5 days.21

Body Stature and Body Mass as Factors in Load Carriage

A service member’s height and weight might be important factors in load 

carriage.2,22 Larger service members might be able to carry heavier loads 

by virtue of their greater bone and muscle mass.23–25 It has been estimated 

that humans have increased their height about 10 cm since the Industrial 

Revolution, possibly because of better nutrition.26 Table 3 provides a 

summary of the heights and weights of various groups derived from a 

variety of sources. Before the British Crimean War, only minimum standards were available. US samples show a progressive increase in height, 

weight, and body mass index since the American Civil War. The increase 

in weight is apparently attributable to an increase in fat-free mass, with 

temporal changes in body fat less consistent. Data on the general US

population suggest that body weight and body mass index have been 

progressively increasing since 1980.27,28 Data on Army recruits suggest 

that the increase in weight is accounted for by about equal increases in 

fat-free mass and body fat.29

14 | Load Carriage in Military Operations
Physiological and Biomechanical 

Aspects of Load Carriage

Although historical studies are useful to show that the problems of load 

carriage have been with the military for a considerable time, it is physiological and biomechanical research conducted during the last 70 years 

that have developed some practical methods to reduce load stress on 

service members. Many general principles and techniques have emerged, 

but studies do not reveal a single way of carrying loads that applies to all 

situations. Commanders must consider the mission, environment, time, 

and terrain to adjust the service members’ burdens.

Load Distribution

There are many ways to carry loads, and the technique used depends on 

the characteristics of the load (size, shape, mass, etc), how far the load may 

be carried, previous experience, and the equipment available to the service 

member.30 Figure 5 illustrates techniques of carrying loads that have been 

directly investigated for individual soldiers.30–37 Team-lifting techniques 

can assist in moving larger loads, as shown in Figures 6 and 7.

Two load-carrying systems currently available to individual US soldiers include (1) the All-Purpose Lightweight Individual-Carrying Equipment (ALICE) pack and (2) the Modular Lightweight Load-Carrying 
Figure 5. Methods of load carriage investigated in various studies.

Photograph: Courtesy of SURVIAC (Survivability/Vulnerabiity Information Analysis Center; 

Wright-Patterson Air Force Base, Ohio)/ARL (US Army Research Laboratory; Adelphi, Md)/

Booz Allen (McLean, Va).

16 | Load Carriage in Military Operations
Figure 6. An Army relief team carries an Army tent in a box to a waiting truck following a 

major earthquake on November 23, 1980. The men are from the 1st Battalion, 509th Infantry 

Regiment, Vicenza, Italy.

Photograph: Courtesy of DefenseImagery.mil. From http://www.defenseimagery.mil/imagery.

html#a=search&s=4%20man%20carry&chk=6cfe0&guid=beed46698d7727f882c43439bd

8bcef71d23261e. 

Equipment (MOLLE) pack. The ALICE pack is more than 35 years old, 

having been introduced within the 1973 to 1974 time frame. The ALICE

pack is durable, stable with heavy loads, and provides ventilation to the 

back because the external frame holds the rucksack away from the body; 

however, adjustment is limited. Studies completed in 199538 showed the 

need for a modular system, with better equipment compatibility and 

features for fitting special equipment. Studies39 resulted in the development and improvement of the MOLLE pack, which was adopted by the 

Marine Corps in 1999 and by the Army in 2001.40 The MOLLE pack 

(Figure 8) is an entire system that consists of a main pack with an external 

frame, butt pack, and load-bearing vest. The main pack has pouches and 

a sleeping bag compartment attached to the external frame. The external 

frame is a lightweight plastic polymer that is anatomically contoured. A 

patrol pack can be detached and used separately. The vest has removable pockets to accommodate different objects. Padded shoulder straps, 

waist belt, and strap adjustments allow for better load distribution, and 

Physiological and Biomechanical Aspects of Load Carriage | 17
Figure 7. Marines carry a stretcher bearing a sniper victim on Guadalcanal in World War II.

Photograph: Courtesy of the National Archives and Records Administration, Archival Research Catalog. From: http://www.pbs.org/thewar/at_war_timeline_1942.htm.

the soldier can shift the load to different anatomical locations. An intermediate system between the ALICE pack and the MOLLE pack was the 

Integrated Individual Fighting System that was introduced in 1988. The 

Integrated Individual Fighting System had a large internal frame pack 

and a tactical load vest, with pockets that allowed more flexibility than 

the ALICE system; however, the internal frame pack was unstable with 

heavy loads (more than 36 kg) and was prone to breakage.40,41

18 | Load Carriage in Military Operations
Figure 8. Soldier wearing the Modular Lightweight Load-Carrying Equipment (MOLLE) 

pack. The MOLLE pack is an entire modular system that includes a main pack with an 

external frame, butt pack, and load-bearing vest. A patrol pack can be detached and used 

separately. The vest has removable pockets to accommodate different objects. Padded shoulder 

straps, waist belt, and strap adjustments allow for better load distribution, and the soldier can 

shift the load to different anatomical locations. 

Photograph: Courtesy of Wikipedia.org. From https://peosoldier.army.mil/factsheets/SEQ_

CIE_MOLLE.pdf. 

Physiological and Biomechanical Aspects of Load Carriage | 19
Backpacks and Double Packs

Where the load is carried on the body will affect both energy cost and 

gait mechanics. Loads can be transported with the lowest energy cost 

(ie, most efficiently) when they are carried on the head.35,42 However, this 

method is impractical for military operations because it requires a long 

training time to learn how to use effectively, is useful only on unobstructed 

horizontal terrain, and produces a high profile (greater body signature). 

A more practical choice is to carry a load as close as possible to the 

center of mass of the body.43–45 In this regard, the backpack and double 

pack methods (Figure 9) have been shown to have a lower energy cost 

than most other forms of load carriage.36,37,46,47 Nonetheless, a backpack 

places most of the load on the back and produces a forward inclination 

of the trunk and head that becomes greater as the load increases.48–51 The 

forward inclination keeps the load-plus-body center of mass over the 

feet (the base of support), but this leads to repetitive contractions (and 

stress) of low back muscles.52,53 Just standing with a backpack increases 

postural sway (anterior-posterior, medial-lateral center of pressure excursions) in a linear manner as the load increases.54 On the other hand, 

Figure 9. A Marine with a double pack at a forward operating base. The marine is from the 

26th Marine Expeditionary Unit and is boarding for a flight back to Kandahar, Afghanistan, 

in support of Operation Enduring Freedom.

Photograph: Courtesy of DefenseImagery.mil. From http://www.defenseimagery.mil. VIRIN: 

020212-M-7370C-126. Photographer: CWO2 William D. Crow, USMC.

20 | Load Carriage in Military Operations
the double pack produces fewer deviations from normal walking than 

does a backpack, including less forward lean of the trunk.49,55 With the 

double pack, increasing load produces a reduction in stride length and an 

increase in stride frequency that is more desirable because it can reduce 

stress on the bones of the foot. In contrast, stride length becomes longer 

as backpack loads increase which, by the same line of reasoning, could 

be potentially harmful.30

Double packs can be useful in some military situations (eg, medics 

carrying their aid bags on the front of their bodies), but backpacks appear to provide greater versatility in military situations. Double packs 

can inhibit movement and limit the field of vision in front of the body, 

making it difficult to see obstructions and traps. They can be burdensome to don and doff; doffing can be very important when sudden or 

unexpected enemy contact occurs. The double pack can also induce 

ventilatory impairments30 and greater heat stress symptoms,56 compared 

with the backpack. The double pack can restrict tasks, such as firing 

weapons and donning protective masks.

Service members can take advantage of what has been learned from 

the double pack by distributing the load more evenly over the torso. Although it is difficult to make the load equal on the front and back of the 

body, both the ALICE and MOLLE systems allow a part of the load to be 

moved forward onto the load-carrying vest. Doing this might be expected 

to reduce energy cost, improve body posture, and reduce injuries.

Pack Frames and Hip Belts

Pack frames and hip belts reduce shoulder stress. The shoulder 

straps of a pack exert pressure on the skin, which can be measured with 

transducers under the straps.57 Shoulder pressure is considerably lower 

with a pack frame incorporating a wide hip belt, compared with a pack 

frame without a hip belt. In one study, 10 kg carried in a frameless pack 

resulted in a peak pressure of 203 mm Hg; the same mass carried in a 

pack with a frame and wide hip belt resulted in a peak pressure of only 

15 mm Hg. The pack with the frame and hip belt produced less electromyographic activity in the trapezius muscle, also suggesting less stress 

in the shoulder area.57 

When a pack frame and hip belt are used for a load between 14 to 41 

kg, the proportion of the load supported on the hips and lower back is 

30% and the load on the shoulders is 70%, regardless of the load mass. 

There is a consistent anterior force exerted on the lower back that might 

increase stress in this area.58 There is some suggestion that experienced 

Physiological and Biomechanical Aspects of Load Carriage | 21
individuals adjust their walking posture to reduce forces and force fluctuations in the shoulder straps.59 Rigid rods attached to both sides of the 

pack and extending into the hip belt transfer about 14% of the vertical 

load from the upper torso to the pelvis.60

Internal frame packs have supporting structures (metal and plastic) 

inside the fabric of the pack and keep the pack closer to the center of 

mass of the body. External frame packs have the supporting structure 

on the outside of the pack, and the pack is usually farther away from 

the center of mass of the body. There is conflicting information regarding whether the internal frame pack has a lower energy cost than the 

external frame pack.61,62 There is no difference in perceived exertion 

between external and internal frame packs when walking on level, even 

terrain.61 However, perceived exertion over rough terrain is lower with 

the internal frame pack.63 

Subjective reports of discomfort vary, depending on the design of 

the pack system. For backpacks with and without frames, the majority 

of discomfort appears to be in the neck and shoulder region, although 

foot discomfort can also be substantial, presumably because of the development of hot spots and blisters.64,65 For a backpack with a hip belt, 

discomfort is localized to the midtrunk and upper legs.66 Overall, when a 

portion of the load is carried on the waist through use of a hip belt, there 

is less subjective discomfort than there is with shoulder load carriage.67

When walking uphill, individuals give higher ratings for balance and ease 

of gait for packs with hip belts that pivot in the sagittal plane.68

Placement of Load in the Backpack

The location of load in the backpack can affect energy cost, subjective comfort, and body mechanics. Using both internal and external 

frame packs, higher energy costs were associated with a load that was 

lower in the pack and farther away from the body; lower energy costs 

were associated with loads placed higher in the pack and closer to the 

body (Figure 10).69,70 However, another study using an external frame 

pack and similar methodology found no difference in energy cost with 

load placements.71 A more even distribution of loads using a rack system 

within the pack resulted in considerably lower ratings of discomfort in 

the neck, shoulders, and lower back.63 

Although both high- and low-load placements bring about forward 

body lean (knees, hips, shoulders, and head are farther forward), this effect is greater for low placements. This is because the lower load is closer 

to the ankles, which requires more forward body rotation to bring the 

22 | Load Carriage in Military Operations
pack center of mass over the feet.72 The additional forward body rotation 

tends to bring the body’s center of mass over the front half of the foot, 

which could increase the likelihood of foot strain and injury.

Nonetheless, placement of the load high in the pack tends to destabilize posture to a greater extent than lower placements, especially among 

tall men, as measured by the amount of body sway while standing with the 

load.73 Dynamic moments are about 40% greater with high-back placement, an affect attributed to the greater rotational inertia of the high load.74

A low- or midback load placement might be preferable for stability 

Pack

Lower Energy Cost

Higher Energy Cost

 = Center of Load Mass

Pack Frame

Figure 10. Effects of load distribution within the pack on energy cost. A high and more anterior load results in a lower energy cost than a low and more posterior load.

Data source: Obusek JP, Harman EA, Frykman PN, Palmer CJ, Bills RK. The relationship 

of backpack center of mass to the metabolic cost of load carriage. Med Sci Sports Exerc. 

1997;29:S205.

Physiological and Biomechanical Aspects of Load Carriage | 23
on uneven terrain, particularly during unexpected stumbles, when highload placement can necessitate relatively high-muscle forces to maintain 

postural stability. The high-load placement might be best for even terrain 

because it keeps body posture with a load most similar to that without 

a load.72

Strap Adjustments

Although not tested experimentally, it is reasonable to assume that 

shifting loads from one part of the body to another during a march can 

improve soldier comfort and allow loads to be carried for longer periods 

of time. Load shifting is accomplished with some pack systems using 

various strap adjustments. Strap adjustments can redistribute the load to 

other muscles or other portions of previously loaded muscles. Portions 

of the body subjected to high-load pressures for long periods of time can 

suffer discomfort, circulatory occlusion, and paresthesis.30,67,75 

Some rucksacks have sternum straps that are attached horizontally 

across both shoulder straps at midchest level. When the sternum strap is 

tightened, it pulls the shoulder straps toward the midline of the body so 

that pressure is shifted more medially. When the sternum strap is loosened, 

the shoulder straps move laterally, and the load is also shifted laterally.

Most pack systems with hip belts and shoulder straps have adjustments that presumably allow more of the load to be placed on the hips or 

shoulders. When the shoulder strap tension is reduced (straps loosened), 

more of the load is placed on the hips. With the shoulder straps tighter, 

more of the load is placed on the shoulders.

Some pack systems have load-lifter straps that attach the top of the 

shoulder straps to the pack frame. When the strap is tightened, the top of 

the load is pulled more anteriorly over the base of support; however, when 

the strap is loosened, the top of the load falls more posteriorly. Other 

strap adjustments that shift load pressures, center the pack, and improve 

lumbar support can further improve soldier mobility and comfort.68

Load Carriage on the Feet, Thighs, and in the Hands

Loads can be carried in places other than the torso, although other body 

positions result in higher energy expenditure. Loads carried on the feet 

result in an energy cost five to seven times higher than an equivalent 

load carried on the upper body.44,76,77 The increase in energy expenditure 

is 7% to 10% for each kilogram added to the foot.44,76–79 This finding 

24 | Load Carriage in Military Operations
suggests that footwear should be as light as possible, compatible with 

durability requirements.

Loads carried on the thigh result in energy costs that are lower than foot 

carriage, but greater than torso carriage. For each kilogram added to the 

thighs (at about midthigh level), the increase in energy cost is about 4%.80,81 

When load masses are carried on the thighs (compared with the feet), less 

mechanical work is performed because of reduced inertia of the body segments; therefore, changes in gait with increasing thigh load are minimal.80

Carriage of loads in the hands also results in a higher energy cost 

than with torso carriage36,46,76 and produces greater cardiovascular 

strain.82 Hand carriage is more efficient than foot carriage because the 

energy cost of carrying loads on the ankles exceeds that of carrying loads 

in the hands by five to six times if the hand load is carried close to the 

body.44 This is likely related to the fact that leg swing is an essential part 

of walking, whereas arm swing is a secondary aspect of gait that can be 

greatly reduced without affecting walking speed. For hand carriage tasks 

(eg, transporting a stretcher), the use of simple shoulder straps or more 

complex harness systems considerably reduce cardiovascular stress and 

result in more subjective comfort.83,84

Rifle Carriage

A rifle will almost always be carried in dismounted military training and 

operations. Rifle carriage restricts arm swing, adds weight, and moves 

the center of mass more anteriorly. During rapid walking (5.4 km/h), a 

4.4-kg rifle (a loaded M16A2 weighs 4.0 kg) has minimal, but significant, 

effects on human gait. There are increases in forces produced at heel strike 

(ground impact forces, about 5%), forces to decelerate the body (maximum breaking forces, about 1%), and side-to-side forces (mediolateral 

impulse, about 12%). Many of these changes are less because of the mass 

of the rifle and are more associated with the restriction of arm movement, 

which increases the movement of the body center of mass.85,86

Body Armor

Individual body armor is commonly worn by soldiers to protect against 

small arms fire and explosive devices. The system currently used is the 

Interceptor Multipurpose Body Armor System, consisting of two major 

Physiological and Biomechanical Aspects of Load Carriage | 25
components: (1) an outer tactical vest (OTV) and (2) small arms protective 

inserts. The OTV is composed of a Kevlar weave and provides protection 

from 9-mm bullets and fragmentation. The OTV has a removable collar, 

throat protector, and groin protector. The small arms protective inserts 

are silicon carbide/boron carbide plates worn in the front and back of the 

OTV, and provide protection from rifle and machine gun fire. Studies87, 88

indicated that additional protection was needed and subsequently developed enhancements included deltoid and axillary protectors providing 

fragmentation and projectile protection over and under the arms (Figure 

11). A medium-sized vest without deltoid and axillary protectors and 

other vest attachments weighs about 13 kg.89,90

As might be expected, the wearing of body armor (compared with 

no body armor) increases perceived exertion, the energy cost of walking, vertical ground reaction forces, and loading rate (change in force 

over time from heel strike to peak impact force)91,92; men and women 

respond in a similar manner.93 As walking velocity increases, the increase 

in energy cost and relative exercise intensity (%V•O2max) is not linear, but 

rather the increase is exponential.92 A vest increases heat stress (core 

temperature, body heat storage) during prolonged (2–4 hours) walking, independent of the increase in energy cost, and a spacer garment 

(to presumably provide “passive cooling”) does not mitigate this heat 

Figure 11. (Left) Interceptor Multipurpose Body Armor System with removable collar, throat 

protector, and groin protector. (Center) Deltoid and (right) axillary protectors, respectively.

Photographs: Courtesy of GlobalSecurity.org. From http://www.globalsecurity.org/military/

systems/ground/interceptor.htm.

26 | Load Carriage in Military Operations
stress.94 Soldiers returning from deployment report deployment-related 

increases in musculoskeletal pain, with 24%, 29%, and 27% of soldiers 

attributing neck, back, and upper extremity pain, respectively, to the 

wearing of individual body armor.89 

Load Carriage Using Carts and Motorized Vehicles

Military personnel seldom consider using wheeled carts to transport 

loads, but, for some missions, this can be an option. In a field trial of 

three manually operated load carts, both positive and negative aspects 

emerged. On the positive side, the tested carts were generally durable; 

able to carry or exceed their rated loads (91–181 kg); and were effectively 

used on flat terrain, in barrier construction, and in resupply. On the negative side, the carts created problems on rugged terrain: they were noisy 

in brush or rocky areas, thus reducing tactical surprise; and equipment 

could get caught in the wheels of some carts.95

A combat load cart appropriate for military operations should have 

a low center of gravity, a wide wheel base, and a large wheel size.96,97 

Compared with body carriage, energy cost was reduced by 88% when 

a 50-kg load was pushed in a cart on a smooth surface.97 Pulled carts 

(rather than pushed) seem to be easier to control on uneven terrain and 

also result in considerable energy cost-savings.96 Over mixed terrain 

(paved road, dirt road, field, and rough trail), a cart pulled by a hip belt 

resulted in 54% faster march times (compared with a rucksack) over 

a 3.2-km distance.98 This latter cart, specifically developed for military 

operations, is available.

Besides carts, removing much of the load burden from the soldier 

can be achieved through the use of a wide variety of motorized vehicles. Systems that have carried soldier equipment in rugged areas in 

Afghanistan have included the Military Gator (or M-Gator; John Deere 

Company, Moline, Ill) and the Polaris Sportsman Military Vehicle (Polaris Industries, Inc, Medina, Minn). The Military Gator is a two-seat, 

six-wheel squad vehicle that can carry up to a 550-kg load and runs on 

JP8 fuel (Figures 12 and 13). The Polaris Sportsman Military Vehicle is 

a four-wheel, all-terrain vehicle that can carry one person and a load up 

to 204.1 kg (Figure 14).99,100 Of course, there will still be terrain that will 

not be suitable for carts or motorized vehicles of any type, and soldiers 

will be personally required to bear the load.5

Physiological and Biomechanical Aspects of Load Carriage | 27
Physiological Factors Associated With Load Carriage

Several studies have examined associations between load carriage and 

various physiological factors using very similar methods. Subjects were 

administered a series of physiological tests to measure physical characteristics, body composition, muscular strength, anaerobic capacity, and 

aerobic capacity. Subjects were asked to complete a given distance as 

rapidly as possible while carrying various load masses. Trip completion 

times were correlated with these physiological measures.

Using univariate correlations, early studies demonstrated low (r = 0.2–0.6), 

but statistically significant, relationships between trip completion times and 

aerobic capacity, back and lower body strength, and fat-free mass.23,101,102

More recent studies using multivariate techniques generally confirm that 

aerobic fitness, fat-free mass, and leg/back strength are important physiological 

factors associated with load carriage performance and changes in load carriage performance.24,25 These studies provide clues as to the components of 

physical fitness that should be trained to improve load carriage performance.

Figure 12. The Military Gator. This is a two-seat, six-wheel squad vehicle that can carry up to 

a 550-kg load and runs on JP8 fuel.

Photograph: Courtesy of Olive-Drab.com. From http://www.olive-drab.com/idphoto/

id_photos_m-gator.php.

28 | Load Carriage in Military Operations
Figure 13. US Army soldiers assigned to the 86th Combat Support Hospital using a Military 

Gator to transport a litter patient at an undisclosed location in Iraq, in support of Operation 

Iraqi Freedom.

Photograph: Courtesy of DefenseImagery.mil. From http://www.defenseimagery.mil. ID: DFSD-04-01753. Photographer: SSGT Quinton T. Burris, US Air Force. 

Physical Training and Load Carriage

Appropriately designed physical training can improve service members’ load carriage capabilities. Walking with backpack loads over 

several weeks results in a decrease in the energy cost of carrying the 

load.103 Australian military recruits with high initial aerobic capacity 

(predicted V•O2max = 51 • mL • kg–1 • min–1) further improved their 

aerobic fitness by engaging in regular backpack load carriage. Loads 

were progressively increased during the 11-week basic training program, and improvements in aerobic capacity were similar to those of 

a control group performing the traditional recruit training program 

involving running.104

Twelve-week physical training programs involving a combination of 

aerobic training (running) and resistance training improved the speed at 

which men completed a 3.2-km distance carrying 46 kg,105 and women 

completed a 5-km distance carrying 19 kg,106 even when these load carriage tasks were not included in the training program. It is interesting that 

Physiological and Biomechanical Aspects of Load Carriage | 29
neither running nor resistance training alone improved march speed,105

suggesting that both aerobic capacity and muscle strength must be trained 

to improve road marching capability. When regular road marching with 

loads (at least twice a month) was included in a training program that 

also involved running and resistance training, service members marched 

faster than if march training was not included.107 Substantial improvements in load-carrying performance were found when civilian women 

were trained with a combination of resistance training, running, and 

load-carrying.108

Figure 14. Polaris Sportsman military vehicle. It is a four-wheel, all-terrain vehicle that can 

carry one person and a load up to 204 kg.

Photograph: Courtesy of Justin Burke, Marketing Manager, Polaris Defense, Medina, Minn. 

From http://www.polarisindustries.com.

30 | Load Carriage in Military Operations
Gender Differences

Compared with men, women walk with shorter stride length and greater 

stride frequency. As loads increase, women’s stride length decreases, 

whereas men’s stride length does not show significant change. With 

increasing load, women also show a more pronounced linear increase 

in the time that both feet are on the ground (double support time) than 

do men. To bring the center of the load mass over the feet (base of support), women tend to hyperextend their necks and bring their shoulders 

farther forward than do men, possibly to compensate for less upper 

body strength. Many of these differences between men and women 

persist even when differences in body size and composition are taken 

into account.40,50

When men and women were asked to complete a 10-km road march 

as quickly as possible carrying loads of 18 kg, 27 kg, and 36 kg (using ALICE packs), men were about 21% faster, regardless of load. On 

systematically administered questionnaires, women commented more 

often than men that the pack straps were uncomfortable, that the pistol 

belts fit poorly, and that the rucksacks (ALICE packs) were unstable. An 

independent predictor of march time (when gender was included in the 

equation) was acromial breadth (shoulder breadth). Because pack systems 

have been designed primarily based on the anthropometry of men, these 

data suggest that pack systems designed considering the anthropometry 

of women can lessen the time gap between men and women.109 Studies 

with the MOLLE pack suggest that the well-padded hip belt allows a 

better transfer of the load to the hips so that women can use the stronger 

muscles of the legs to carry the load.40,58 This might assist in improving 

female load carriage performance.

Predicting the Energy Cost of Carrying Military Loads

Studies conducted on treadmills for short periods of time show that 

energy cost increases in a systematic manner, with increases in body 

mass, load mass, velocity, grade, or a combination of these items.110–116 

Type of terrain also influences energy cost, as shown in Figure 15.96,117,118

Pandolf and colleagues119 expanded on the work of Givoni and Goldman120 to develop an equation (1) to predict the energy cost of load 

carriage:

Physiological and Biomechanical Aspects of Load Carriage | 31
Mw = 1.5 • W + 2.0 • (W + L) • (L/W)

2

 +

(1) T • (W + L) • (1.5 • V2 + 0.35 • V • G),

where Mw = metabolic cost of walking (Watts), W = body mass (kg), L = 

load mass (kg), T = terrain factor (1.0 = blacktop road, 1.1 = dirt road, 

1.2 = light brush, 1.5 = heavy brush, 1.8 = swampy bog, 2.1 = loose 

sand, snow [dependent on depth of depression {T = 1.30 + 0.082 • D, 

where D = depression depth in centimeters}]),117 V = velocity or walk rate 

(m/sec), and G = slope or grade (%).

The Pandolf equation has been independently validated using a 

range of loads and body masses.121 However, the equation has several limitations. First, it does not predict accurately the energy cost of 

downhill walking.122,123 Downhill walking energy cost approximates a 

U-shape when plotted against grade: it initially decreases, then begins 

Figure 15. Effects of terrain on energy cost. Energy cost increases about 8% on a dirt road and 

about 24% for moving through light brush. Much heavier brush requiring the use of arms and 

more lifting of the legs to move over downed trees and brush can increase energy cost by 60%. 

Going through swampy land or walking on sand almost doubles energy cost. Walking in snow 

without the use of snowshoes can considerably increase energy cost 3 or 4 times, depending on 

the depth and quality of the snow. This increase in energy cost with deeper snow is presumably 

because of the extra energy needed to raise the legs. Numbers after the snow estimates are the 

depth of depression the shoe makes in the snow.

Data sources: Haisman MF, Goldman RF. Effect of terrain on the energy cost of walking with 

back loads and handcart loads. J Appl Physiol. 1974;36:545–548. Pandolf KB, Haisman MF, 

Goldman RF. Metabolic energy expenditure and terrain coefficients for walking on snow. 

Ergonomics. 1976;19:683–690. Soule RG, Goldman RF. Terrain coefficients for energy cost 

prediction. J Appl Physiol. 1972;32:706–708.

32 | Load Carriage in Military Operations

40

30

20

10

0

VO2 (ml/kg/min)

Treadmill

Paved Road

Dirt Road

Light Brush

Heavy Brush

Swamp

Sand

Snow (10 cm)

Snow (20 cm)
to increase.124–126 The lowest energy cost occurs between –5% to –15%, 

depending on individual gait characteristics.124,126 Santee and colleagues126

developed an empirical model to predict the energy cost of downhill walking. The model assumes that the initial reduction in downhill walking 

energy cost is from the negative work of gravity, but that this is reduced 

by the eccentric action of the muscles to decelerate the body and energy 

absorbed by the muscles and joints. Equation (2) is as follows:

(2) Wtd = Wl+ (2.4 (mt • g • h • s–1) • 0.3(α/7.65)),

where Wtd = total metabolic cost (Watts), Wl = metabolic cost of level 

walking (Watts), mt = total load mass (kg), g = acceleration caused by 

gravity (9.8 m/s2), and α = grade or slope for negative work.

A second limitation of the Pandolf equation might be that it does not 

account for increases in energy cost over time. In studies used to develop 

the equation, energy cost was examined for short periods, usually less 

than 30 minutes. Most studies127–129 have shown that the energy cost of 

prolonged (≥2 h) load carriage at a constant speed increased over time 

at higher loads, or speeds or both. Energy cost also increases over time 

during downhill walking with loads.129 Whether or not energy expenditure 

increases over time is important, because the individual carrying the load 

might become more easily fatigued if energy cost does increase.

Physiological and Biomechanical Aspects of Load Carriage | 33

Medical Problems Associated 

With Load Carriage

Injuries associated with load carriage, although generally minor, can 

adversely affect an individual’s mobility and thus reduce the effectiveness of an entire unit. Tables 4 and 5 show the results of two studies that 

recorded acute injuries during military road marching operations.130,131 

Foot blisters, back problems, and metatarsalgia were the most common 

march-related injuries. These injuries are similar to those self-reported 

by recreational hikers who generally carry lighter loads, but the relative 

frequency is somewhat different.132–134 Table 6 summarizes common load 

carriage-related injuries, as well as prevention and treatment strategies.

Foot Blisters

Foot blisters are the most common load-carriage-related injury65,131,135–137

(Figure 16). They result from friction between the socks and skin,138–140

a product of point pressures exerted by the boot and the foot. Blisters 

can cause extreme discomfort, prevent service members from completing 

marches, and can lead to many days of limited activity.131,141,142 If they are 

not properly managed, especially in field conditions, they can progress 

to more serious problems, such as cellulitis or sepsis.141,143
Heavy loads increase blister incidence,109,137,144 possibly by increasing 

pressure on the skin and causing more movement of the foot inside the 

boot through higher propulsive and breaking forces.49,145 Rifle carriage 

alone has minor effects on maximal breaking and propulsive forces.85

Other blister risk factors include tobacco use, low aerobic fitness, and 

ethnicity other than black.130,146

When loads are very heavy (>61 kg), the double pack has been shown 

to demonstrate a lower blister incidence than the backpack,147 suggesting 

Table 5. Injuries Among 218 Infantry Soldiers During a 5-Day, 161-km Road March130

During March* Totals

Soldier Continued Soldier Did Not 1–15 Days

Injury March (n) Continue March (n) Post-march (n)† N %

Foot blisters 43 3 3 49 48

Metatarsalgia 8 2 9 19 19

Back pain/strain 4 1 1 6 6

Sprains 2 3 0 5 5

Knee pain 3 1 3 7 7

Ingrown toenail 0 3 0 3 3

Stress fracture 0 1 0 1 1

Other 8 3 1 12 12

Total 68 17 17 102 100

*From physician’s assistants at fixed medical sites along the march.

†From medical records after the march.

36 | Load Carriage in Military Operations

Table 4. Injuries Among 355 Infantry Soldiers During a 20-km Maximal Effort Road March131

During March* Totals

Soldier Continued Soldier Did Not 1–12 Days

Injury March (n) Continue March (n) Post-march (n)† N %

Foot blisters 16 0 19 35 38

Back pain/strain 5 7 9 21 23

Metatarsalgia 1 1 9 11 12

Leg strain/pain 0 0 7 7 8

Sprains 1 1 4 6 7

Knee pain 0 0 4 4 4

Foot contusion 0 1 1 2 2

Other 1 2 2 5 5

Total 24 12 55 91 100

*From medics and physician during the march.

†From medical records after the march.
Table 6. Summary of Common Load Carriage-Related Injuries With Prevention and 

Treatment Strategies*140,177

Signs

Injury and Symptoms Prevention Treatment

Foot blisters Elevated area, 

lighter in color 

than surrounding 

skin, and filled 

with fluid; pain, 

burning, warmth, 

and erythema

1. Use acrylic, nylon, or 

polyester inner sock; use 

thick, snug, dense-weave 

outer sock with inner sock

2. Use Spenco† insoles

3. Utilize antiperspirants

4. Make sure that load 

distribution is more evenly 

around the body center of 

mass

5. Reduce load mass

6. Precondition feet through 

physical training and 

road march practice

7. Improve aerobic fitness 

8. Cease smoking/tobacco use

9. Cover skin when hot spots 

appear

Intact blister: drain, leave 

top in place, and use light 

pressure dressing

Torn blister: remove top, use 

antibiotic ointment, and put 

on surgical bandage 

Use hydrogel or hydrocolloid dressings; also polyurethane films

Metatarsalgia Pain, swelling on 

sole of foot

1. Precondition feet through 

physical training and 

road march practice

2. Reduce load mass

RICE‡

Antiinflammatory medication§

Stress fractures Persistent, bony 

pain; well-circumscribed palpable 

area of bony 

tenderness

1. Cease smoking/tobacco use

2. Precondition feet and legs 

through physical training 

and road march practice

RICE

Antiinflammatory medication

Knee pain Pain, swelling, 

crepitus, and 

instability

1. Perform lower extremity 

strengthening and stretching

RICE

Antiinflammatory medication

Low-back pain Pain, muscle 

spasm, and neurological symptoms

1. Be sure that load distribution is more evenly around 

the body center of mass

2. Reduce load mass

3. Perform trunk and abdominal strengthening

RICE

Antiinflammatory medication

Rucksack palsy Upper extremity 

numbness, paralysis, and cramping; 

scapular winging

1. Use framed rucksack

2. Utilize hip belt on rucksack

3. Employ load shifting via 

strap adjustments

RICE

Antiinflammatory medication

Meralgia 

paresthetica

Pain, paresthesia, 

and weakness in 

the anterolateral 

thigh

1. Use properly fitted body 

armor

2. Avoid compressing thighs 

with lower edge of body 

armor

Reduce body armor wear

Antiinflammatory medication

*See text for full descriptions and applications.

†Spenco Medical Corporation, Inc, Waco, Tex.

‡RICE: Rest, Ice, Compression, Elevation

§Antiinflammatory medication refers to aspirin or a nonsteroidal antiinflammatory drug.

Medical Problems Associated With Load Carriage | 37
that better load distribution can reduce blisters. Spenco shoe insoles 

(Spenco Medical Corporation, Inc, Waco, Tex) have also been shown to 

reduce foot blister incidence, possibly because they absorb frictional forces 

in anteroposterior and mediolateral directions.148–150 Regular physical 

training with load carriage induces skin adaptations that reduce the probability of blisters.140 Thus, blisters can be less of a problem in units that 

march regularly; however, sudden increases in march intensity or distance 

will probably make blisters more likely, regardless of training regularity.

Moist skin increases frictional forces and probably increases blister 

incidence.140,141,151 Acrylic socks decrease the number and size of blisters,152

possibly by conducting sweat away from the foot.153 A nylon sock worn 

inside a wool sock reduces the incidence of blisters on soldiers who are 

road marching.154,155 Polyester socks alone, or a thin polyester sock worn 

inside thicker socks (that are either wool-polypropylene or other such 

moisture-wicking wool blend materials), reduce foot blister incidence 

during military training.156,157

Figure 16. Friction blisters on the foot.

Photograph: Courtesy of Wikimedia Commons. From http://commons.wikimedia.org/wiki/

File:Friction_Blisters_On_Human_Foot.jpg. 

38 | Load Carriage in Military Operations
Antiperspirants also reduce foot sweating,158,159 and some anecdotal 

reports and case studies suggest they might be effective in reducing 

blisters.160–162 A 20% solution of aluminum chloride hexahydrate in an 

anhydrous ethyl alcohol base (eg, Drysol, Person & Covey, Inc, Glendale, 

Calif) was effective in reducing the likelihood of march-related blisters 

when the preparation was applied to the entire foot for at least three 

nights before a march.163 Once the antiperspirant effect has been achieved, 

it can be maintained with applications once per week.164 However, many 

individuals report irritant dermatitis using this preparation,163 which 

can require the application of a topical steroid. Other options in this 

case include using a lower concentration preparation (eg, Xerex, Person 

& Covey, Inc, Glendale, Calif), changing the treatment schedule (using 

the same number of applications, but over a longer period of time), or 

discontinuing use. Antiperspirants in emollient bases are not effective 

in reducing blisters, presumably because emollients interfere with the 

antiperspirant effect.165

Soldiers typically experience areas of friction known as “hot spots,” 

the subjective experience of which is a localized warm or burning sensation. This presumably preblister stage is characterized as a local red 

(erythema) and tender area (Figure 17). When hot spots are detected, 

blisters may be avoided by shielding the affected area with a low-friction 

skin covering. Various skin coverings have been examined for their coefficients of friction (μ), and lower μ values may be more effective in reducing blister incidence. Tested skin coverings (with μ values in brackets) 

include the following:

• Bursatec (Bursatec, Mexico City, Mexico)[0.57], 

• Dr. Scholl’s Moleskin Plus (Schering-Plough HealthCare Products, 

Inc, Memphis, Tenn) [0.69],

• Moleskin [0.94], 

• Band-AidBrand Adhesive Bandages (Johnson & Johnson Consumer 

Companies, Inc, New Brunswick, NJ) [1.01], 

• Band-Aid Plastic Bandages [1.03], 

• Spenco 2nd Skin Blister Pad [1.04], 

• New-Skin (Prestige Brands, Inc, Irvington, NY) [1.05], 

• Nexcare Comfort Bandage (3M Company, St Paul, Minn) [1.08], 

• Dr. Scholl’s Blister Treatment [1.20], 

• Band-Aid Blister Block [1.37], and 

• Tegaderm (3M Company, St Paul, Minn) [1.54].166

Medical Problems Associated With Load Carriage | 39
Another option is a doughnut pad or covering (eg, DuoDERM, ConvaTec, 

Inc, Skillman, NJ), which should be applied to reduce friction and possible blister development.167

There are few studies of blister treatment, and care is based on clinical 

experience and common sense. Small blisters (<5 mm) are usually selflimiting and should not be drained unless they are painful, because of the 

risk of infection.168 A small, doughnut-shaped moleskin pad can be placed 

over the blister to prevent rupture. If the blister is larger than 5 mm and 

on a weight-bearing area, it should be drained. To promote blister-top 

adhesion and healing, blister drainage should occur at the proper time. 

For blisters less than 24 hours old, several punctures should be made with 

a sterile needle or a no. 11 surgical blade (Figure 18). For older blisters, 

Figure 17. A “hot spot” on the medial aspect of a soldier’s foot during a road march.

40 | Load Carriage in Military Operations
a single puncture is recommended.169 Tops should be kept in place to 

serve as functional dressings.170 A pressure dressing (eg, gauze pad and 

adhesive tape) can be applied to ensure that the blister roof adheres to the 

underlying tissue. If the top of the blister is almost completely torn off, 

it should be removed171 and the site treated as an open wound. In addition to antiseptic treatments (eg, antibiotic ointment), a surgical bandage 

should be applied.169 For smaller blisters, a doughnut-shaped moleskin 

pad affixed with a porous adhesive knit cover (eg, Coverlet, BSN-Jobst, 

Charlotte, NC) will protect the blister as shown in Figure 19; for larger 

blisters, a larger dressing will be needed.162,164 Hydrogel dressings (Figure 

20) (eg, Spenco 2nd Skin) or polyurethane films (eg, Tegaderm) can be 

affixed to the blister and covered with a pad and tape.169,172 Hydrocolloid dressings, such as DuoDERM (ConvaTec, Inc), can also be helpful 

in allowing mobility173 and promoting healing.172,174,175 

Medical Problems Associated With Load Carriage | 41

Figure 18. Friction blisters showing suggested puncture sites to drain the blister. For blisters less 

than 24 hours old, several punctures should be made with a sterile needle or a no. 11 surgical blade.

Illustration: Courtesy of Heidi Moncrief, Healthwise, Inc, Boise, Idaho. From

http://64.143.176.9/library/healthguide/en-us/images/media/medical/hw/hwkb17_072.jpg.
Figure 19. Treatment for smaller blisters. A doughnut-shaped moleskin pad affixed with a 

porous adhesive cover (eg, Coverlet, BSN-Jobst, Charlotte, NC) will protect the blister.

Illustration: Courtesy of the US Army Research Institute of Environmental Medicine (Natick, 

Mass).

Antiseptic

ointment

Adhesive

cover

Doughnut moleskin pad

42 | Load Carriage in Military Operations

Figure 20. Other ways of protecting blisters. Hydrogel dressings such as Spenco 2nd Skin 

(Spenco Medical Corporation, Waco, Tex) or a polyurethane film such as Tegaderm (3M 

Company, St Paul, Minn) can be afixed to the blister and covered with a pad and tape.

Illustration: Courtesy of the US Army Research Institute of Environmental Medicine (Natick, 

Mass).

Adhesive tape

Gauze pad

Hydrogel dressing
Metatarsalgia

Metatarsalgia is a descriptive term for nonspecific, painful overuse injury 

of the foot. The usual symptom is localized tenderness on the sole of the 

foot under the second or third metatarsal head (Figure 21). Sutton176

reported a 20% incidence of metatarsalgia during a strenuous 7-month 

Airborne Ranger physical training program that included regular load 

carriage. One study131 reported a 3.3% incidence of metatarsalgia after 

a single, strenuous 20-km walk with soldiers carrying 45 kg. 

Metatarsalgia is usually associated with foot strain caused by rapid 

changes in the intensity of weight-bearing activity.177 Walking with heavy 

loads can be a predisposing factor for metatarsalgia, because this might 

cause the foot to rotate anteroposteriorly around the distal ends of the 

metatarsal bones for more prolonged periods of time, thus resulting in 

more mechanical stress in this area.49

Treatment is conservative and includes rest, use of ice packs, elevation 

of the foot, and antiinflammatory medications. A metatarsal pad can be 

used. If symptoms persist, despite these conservative measures, further evaluation for more serious problems (eg, fractures, tumors) is warranted.178

Stress Fractures

Lower extremity stress fractures are common in military recruits179–184

and have also been reported in trained soldiers.184 During the Central 

Burma campaign in World War II, 60 stress fracture cases were reported 

in one infantry unit during a 483-km road march.185

Stress fractures are attributable to repetitive overloading of bones 

during activities, such as road marching. The most common areas of 

involvement are the lower extremities, especially the tibia, tarsals, and 

metatarsals.179,185–190 For metatarsal stress fractures, tenderness is generally 

localized on the dorsal side of the metatarsal shafts, which distinguishes 

the pain from metatarsalgia (Figure 22). Figure 23 shows x-ray films of 

a metatarsal stress fracture when the patient first presented and 3 weeks 

later. Generally, a period of time is necessary before stress fractures are 

apparent on x-ray films. 

Demonstrated risk factors for stress fractures include the 

following: 

Medical Problems Associated With Load Carriage | 43
• female gender,179,184,191–194

• white ethnicity,179,195–197

• older age,179,196,197

• taller body stature,182

• high foot arches,198,199

• low aerobic fitness,192,196

• prior physical inactivity,182,196,197 

• older running shoes,197 

• genu varus,200 and 

• cigarette smoking.195,201 

Other factors that might increase risk include load carriage distance184,202

and walking style.182,203 

A number of interventions have been tested in an effort to reduce 

the incidence of stress fractures.191,197,204–210 All studies were conducted 

in basic combat training. Successful interventions include reduced 

running mileage,204 neoprene boot insoles,206 and calcium/vitamin D

supplementation.211,212 A multiple intervention study in Australian basic 

training demonstrated that reducing march speed, allowing trainees to 

march at their own step length (rather than marching in step), running 

and marching in more widely spaced formations, running on grass, and 

Figure 21. Sites of metatarsalgia. The usual symptom is 

localized tenderness on the sole of the foot under the second 

or third metatarsal head. 

Illustration: Courtesy of the US Army Research Institute of 

Environmental Medicine (Natick, Mass).

Sites of

tenderness

Sole of foot

44 | Load Carriage in Military Operations
reducing running mileage were successful in reducing female pelvic stress 

fractures.205

Stress fracture treatment includes a long period of rest, use of ice 

packs, and antiinflammatory medications. If the patient has to be mobile, 

crutches are necessary.

Knee Pain

Knee pain is another condition that has been associated with load carriage. Dalen and colleagues213 reported a 15% incidence of knee pain 

(17 cases of 114 subjects) during their load carriage study. Knapik and 

colleagues131 reported only a 0.6% incidence of knee pain (2 cases of 335 

subjects) following a single strenuous walk, but the two cases resulted in 

a total of 14 days of disability.

Knee pain is difficult to diagnose. Various disorders include patellofemoral pain syndrome, patellar tendonitis, bursitis, and ligamentous 

Figure 22. Symptom of metatarsal stress fracture. Tenderness is generally localized on the 

dorsal side of the metatarsal shafts, which distinguishes the pain from metatarsalgia.

Medical Problems Associated With Load Carriage | 45
strain. These conditions can arise from an abrupt increase in road marching mileage or intensity or from climbing hills if service members have 

not been conditioned for this activity. Treatment includes rest, use of ice 

packs, and antiinflammatory medications. Quadriceps and hamstring 

strengthening and stretching exercises, along with heel cord stretching, 

may be important to prevent recurrence.214

Low Back Injuries

Low back injuries can pose a significant problem during load carriage. In 

one study,131 50% of the soldiers who were unable to complete a strenuous 20-km walk reported problems associated with their backs. Dalen 

and colleagues213 reported frequent problems with back strain during 

a 20- to 26-km walk. Low back injuries are difficult to define because 

the pain might result from trauma to a variety of structures, including 

Figure 23. X-ray films of a metatarsal stress fracture when the patient first presented to the 

clinician (left) and 3 weeks later (right). 

Photographs: Courtesy of Keith G. Hauret, MSPH, MPT.

46 | Load Carriage in Military Operations
spinal discs, the ligaments connecting the vertebral bodies, nerve roots, 

or supporting musculature.177

Heavy loads can be a risk factor for back injuries.137 This could be because heavier loads lead to changes in trunk angle, which can stress back 

muscles,52,53,215 or because heavier loads do not move in synchrony with 

the trunk,53,216 thus causing cyclic stress of the back muscles, ligaments, 

and spine.52,53 Framed packs exert a consistent anterior force on the lower 

back, and it has been suggested that this force could contribute to low 

back pain and soreness.58 Walking with a frameless pack for a relatively 

short period of time (18 min) results in a greater anterior curvature of the 

spine, which could result in moments of greater posterior-compressive/

anterior-tensile forces on intervertebral discs.217 The double pack can 

help reduce the incidence of back problems because it results in a more 

normal posture and eliminates prolonged bending of the back.49,58 Thus, 

better load distribution could reduce back injuries. Also, a general overall strengthening and warm-up program involving the back, abdomen, 

hamstrings, and hip muscles can assist in prevention.177

Rucksack Palsy

Rucksack palsy is a disabling injury that has been widely reported in 

association with load carriage.75,176,218–225 The incidence of rucksack 

palsy was reported to be, respectively, 1.2/1,000 and 0.2/1,000 in US

Army basic training when wearing a rucksack alone versus a rucksack 

with a frame and hip belt218; the incidence in Finnish basic training was 

reported to be 0.5/1,000 recruits.226 It is hypothesized that the shoulder 

straps of a backpack or the top portion of individual body armor when 

in certain postures can cause a traction injury of the C5 and C6 nerve 

roots of the upper brachial plexus. In minor cases, compression results 

in entrapment of the long thoracic nerve. Symptoms include numbness, 

paralysis, and cramping, and minor pain in the shoulder girdle, elbow 

flexors, and wrist extensors. Long thoracic nerve injuries usually present 

with “scapular winging” (Figure 24) because of weakness of the serratus 

anterior muscle. Sensorimotor deficits from rucksack palsy injuries are 

usually temporary, but, in some cases, can result in a chronic condition. 

Nerve conduction studies and electromyographic studies might be necessary to document this condition.218,221

Use of a backpack frame and hip belt has been demonstrated to reduce the incidence of rucksack palsy,218 presumably by reducing pressure 

Medical Problems Associated With Load Carriage | 47
on the shoulders.57,58 Hypothetical risk factors for rucksack palsy 

include heavy loads, improper load distribution, and longer carriage 

distances.137,218 Height, weight, body mass index, or aerobic fitness were 

not risk factors in Finnish basic training.226

Meralgia Paresthetica

Meralgia paresthetica is an abnormal condition characterized by pain and 

paresthesia in the outer anterolateral thigh. It is caused by a compression 

of the lateral femoral cutaneous nerve, a sensory nerve branch of the L2/

L3 spinal area. A recent report of two cases of this disorder suggests that 

when soldiers are wearing body armor and are seated for long periods, 

the lower edge of the body armor may compress the inguinal region, 

thus resulting in a compression of the lateral femoral cutaneous nerve 

and leading to pain and paresthesia. Symptoms generally resolve with 

removal of the chronic compression.227

48 | Load Carriage in Military Operations

Figure 24. Scapular winging.

Photograph: Courtesy of Wikipedia.org. From http://en.wikipedia.org/wiki/

File:Wingingofscapula.jpg.
Influence of Load Carriage 

on the Performance of Other 

Tasks

A significant consideration from a military perspective is how well service members are able to perform military tasks during load carriage. 

Load mass, load volume, and load distribution seem to be important 

variables. As the mass increases, there are systematic decrements in the 

performance of specific tasks (eg, short sprints, agility runs, ladder climbs, 

and obstacle courses).67,228 The decrement in performance of such tasks is 

estimated at about 1% per kilogram load.67 Loads of greater volume will 

inhibit movement under obstacles. The distribution of the load within the 

backpack can also influence performance of specific tasks.67 Wearing of 

individual body armor (10 kg) results in increased perceived exertion and 

decrements in pull-up performance, flexed arm hang time, and maximal 

stair-stepping ability,91 which may be relevant to some soldier tasks like 

climbing over obstacles and movements in urban buildings.

In some operations, service members are required to walk long distances and perform critical military tasks at the completion of the march. 

Very strenuous marches (maximal speed with loads of 34–61 kg over 

10- to 20-km distances) lead to postmarch decrements in marksmanship 

and grenade-throwing distance.64,109,144 Decrements in marksmanship 

are presumably attributable to small movements of the rifle, resulting 

from fatigue of the upper body muscle groups, fatigue-induced tremors, 
or elevated heart rate or respiration.64,144,229 The decrements in grenadethrowing distance might be from nerve entrapment syndrome218,221 or 

pain in the shoulder area, both resulting from pressure of the rucksack 

straps. Lower body muscular power (as measured by the vertical jump 

and Wingate’s Anaerobic Test [which measures anaerobic capacity using 

a bicycle ergometer]) and muscle strength do not appear to be adversely 

affected by prolonged pack load carriage.64,109,144,230

50 | Load Carriage in Military Operations
Summary

There are several ways to improve military load carriage. The techniques 

most available to unit commanders are load reduction, load redistribution, and physical training. Load reduction can be accomplished by tailoring the load to the specific objective and by using special load-handling 

devices. Commanders must make realistic risk analyses and then take 

only the equipment necessary for the mission. Special combat load carts 

are available that could be useful in special situations (eg, marches on 

unobstructed terrain or in close resupply operations).

Load redistribution can be accomplished by placing equipment more 

evenly around the torso. Current load carriage systems have attachment 

points and pockets that can be useful for moving some items from the 

rucksack to the front of the body. Items carried on the front of the body 

should be those likely to be needed suddenly or needed often. The most 

advantageous distribution of the load in the pack might depend on the 

type of terrain. On roads or well-graded paths, placement of heavy items 

high in the pack is preferable for maintaining a more upright body posture and reducing low back problems. On uneven terrain, a more even 

distribution of the load within the pack is more helpful to maintain stability. Load reduction and redistribution can reduce energy cost, decrease 

injuries, and improve performance on tasks following load carriage.

Physical training that includes aerobic exercise, resistance exercise, 

and road marching should be performed on a regular basis. Appropriate 

programs can be tailored to unit needs based on previously successful 
programs. Road marching should be conducted at least twice each 

month, with loads that service members will be expected to carry in unit 

operations (this could be in place of regular physical training). Load and 

distance should be increased gradually over sessions until a maintenance 

level has been achieved. New unit members should be given time to adapt 

through the same gradual program. Regular physical training has been 

shown to increase march performance and might reduce injuries.

To some extent, the selection and proper use of equipment can assist 

in reducing load-carrying stress. The MOLLE pack has a frame with a 

well-padded hip belt that reduces pressure on the shoulders, results in 

less perceived strain, and reduces the incidence of some injuries. Frames 

and hip belts can improve service members’ performance on tasks requiring use of the upper body. Equipment such as the sternum strap on the 

MOLLE packs reduces stress by allowing pressure to be distributed to 

other parts of the body. The MOLLE pack also provides some ventilation 

across the back because of its external frame construction. New load 

carriage technologies that are being tested and will become available will 

use many of the ideas and principles discussed in this monograph. 

It is desirable to reduce load carriage-related injuries that impair 

performance, cause discomfort and disability, and result in a loss of manpower. The use of hip belts can reduce the incidence of rucksack palsy. 

Keeping the feet dry using an acrylic, polypropylene, or nylon inner socks 

combined with wool or wool-polypropylene outer socks will reduce the 

incidence of blisters. Antiperspirants (applied for at least three consecutive 

days before a march) and frequent changes of socks can also be helpful. 

Blister incidence can be reduced by using Spenco insoles (Spenco Medical 

Corporation) and by distributing the load more evenly around the torso 

(both of which can reduce frictional forces around the foot). Physical 

training directed at improving aerobic fitness, along with regular load 

carriage marches, can reduce the incidence of stress fractures and blisters. 

In basic training, stress fractures can also be controlled by using neoprene 

insoles, limiting running mileage, allowing trainees to march at their own 

stride length, and using more widely spaced formations.

Making loads lighter, improving load distribution, using appropriate physical training, selecting proper equipment, and choosing specific 

techniques directed at injury prevention will all facilitate load carriage. 

Suitable changes will allow service members to continue missions at 

lower energy costs and with fewer injuries, and be better able to perform 

other tasks.

52 | Load Carriage in Military Operations
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