Biomechanical and Physiological Validation of the OmniDirectional Treadmill Upgrade as a Mobility 

Platform for Immersive Environments 

by Angela C. Boynton, Kathy L. Kehring, and Timothy L. White 

ARL-TR-5510 April 2011 

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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5425 

ARL-TR-5510 April 2011 

Biomechanical and Physiological Validation of the OmniDirectional Treadmill Upgrade as a Mobility 

Platform for Immersive Environments 

Angela C. Boynton, Kathy L. Kehring, and Timothy L. White 

Human Research and Engineering Directorate, ARL 

Approved for public release; distribution is unlimited. 
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Biomechanical and Physiological Validation of the Omni-Directional Treadmill 

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14. ABSTRACT 

A novel mobility platform, the Omni-Directional Treadmill (ODT) Upgrade, has been developed to allow users to move 

through a virtual environment in a manner equivalent to doing so in the real world. The purpose of this investigation was to 

determine the extent to which walking on the ODT Upgrade is comparable to walking overground for selected biomechanical 

and physiological variables. Temporal-spatial parameters, sagittal plane joint kinematics, and metabolic cost were assessed for 

10 subjects as they walked along identical circular courses overground and on the ODT Upgrade. Except for a reduction in 

ankle plantarflexion following toe-off on the ODT Upgrade, differences in gait mechanics between the overground and ODT 

Upgrade trials were relatively small. However, oxygen consumption was more than 20% greater during walking on the ODT 

Upgrade than overground, and must be taken into account when comparing the results of training and research conducted on the 

ODT Upgrade to that of the real world. Future studies are required to develop a better understanding of the potential 

mechanisms behind this substantial increase in metabolic cost. In conclusion, the ODT Upgrade permits users to walk through 

a virtual environment in a relatively natural way but with a significant increase in physiological demand. 

15. SUBJECT TERMS

omni-directional treadmill, gait, metabolic cost, immersive simulation, mobility interface 

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Angela C. Boynton 

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iii

Contents 

List of Figures v

List of Tables vi

1. Introduction 1

1.1 Background .....................................................................................................................1

1.2 Conventional Treadmills .................................................................................................1

1.3 Omni-Directional Treadmills ..........................................................................................2

1.4 Objective .........................................................................................................................5

2. Materials and Methods 5

2.1 Participants ......................................................................................................................5

2.2 Instrumentation ................................................................................................................5

2.2.1 Immersive Environment Simulator .....................................................................5

2.2.2 Three-Dimensional Motion Capture ...................................................................6

2.2.3 Physiological Demand Assessment .....................................................................7

2.3 Data Collection Protocol .................................................................................................8

2.4 Data Reduction and Analysis ..........................................................................................9

2.5 Statistical Analyses........................................................................................................11

3. Results 11

3.1 Temporal-spatial ............................................................................................................11

3.2 Kinematics .....................................................................................................................12

3.3 Metabolic Cost ..............................................................................................................15

3.4 Ratings of Perceived Exertion .......................................................................................16

3.5 Motion Sickness Questionnaire Response ....................................................................16

4. Discussion 17

5. Conclusions 20

6. References 21
iv

Appendix A. Motion Sickness Questionnaire 23

Appendix B. Borg Scale 25

Distribution List 27
v

List of Figures 

Figure 1. First-generation ODT (a) and first-generation ODT belt configuration (b). ...................3

Figure 2. ODT Upgrade (a) and ODT Upgrade belt configuration (b). ..........................................4

Figure 3. Immersive environment simulator. ..................................................................................6

Figure 4. Placement of tracking and anatomical markers. ..............................................................7

Figure 5. The participant wears a facemask and Cosmed K4b2. ....................................................8

Figure 6. The participant follows an investigator during the overground trials (a) and a 

virtual 3 entity during ODT Upgrade trials (b). .........................................................................8

Figure 7. Mean sagittal plane hip, knee, and joint angles during walking at 1.12 m/s 

overground and on the ODT. Shaded area represents 1 standard deviation above and 

below the overground mean. ....................................................................................................13

Figure 8. Mean sagittal plane hip, knee, and joint angles during walking at 1.34 m/s 

overground and on the ODT. Shaded area represents 1 standard deviation above and 

below the overground mean. ....................................................................................................14

Figure 9. Metabolic cost during walking overground and on the ODT. .......................................16
vi

List of Tables 

Table 1. Participant characteristics. ................................................................................................5

Table 2. Temporal-spatial parameters. ..........................................................................................12

Table 3. Sagittal plane joint angle normalcy during walking on the ODT. ..................................15
1

1. Introduction 

Technological advances in computer graphics combined with the development of large rearprojection surround displays have enabled the creation of virtual environments that visually 

immerse the user into a sense of real-world presence. Integration of these visual displays with a 

mobility interface that enables the user to move through the virtual environment provides 

instrumentation for more interactive applications. The mobility interface can be as simple and 

abstract as a mouse or a joystick. However, given their inability to provide appropriate effects 

on the user from the physical workload of traversing terrain and their distraction from the 

psychosomatic immersion into the environment, these interfaces may not be adequate for 

applications that require or benefit from natural human locomotion through the threedimensional (3-D) environments. A simulation environment that provides a realistic perception 

of movement and the effects of fatigue would enhance the U.S. Army’s ability to gain insight 

into the physical, physiological, and cognitive processes of dismounted Soldiers when placed in 

demanding, stressful operational situations. It would provide a means to explore new operational 

tactics or equipment concepts in a highly configurable, repeatable, and safe manner and to collect 

data that would be difficult or impossible to gather from real-world exercises. 

1.1 Background 

Over the years, more complex mobility platforms have been developed, attempting to achieve 

greater equivalence between the user’s motions on the device and those used in the real 

environment. These designs have ranged from unicycle-type devices, to standing bipedal 

devices, to treadmill-based devices (Crowell et al., 2006). The Omni-Directional Treadmill 

(ODT), which allows the user to turn and travel in any direction without leaving a confined 

workspace, is one device that shows promise for providing natural locomotion to the user. 

However, to be truly effective at simulating the real-world experience of traversing the 

environment, the biomechanical and physiological effects on the user should be the same as 

those in the real world. 

1.2 Conventional Treadmills 

Over the past three decades, multiple biomechanical and physiological evaluations have been 

conducted between walking overground and on a conventional treadmill (Alton et al., 1998; Lee 

and Hidler, 2008; Murray et al., 1985; Parvataneni et al., 2009; Pearce et al., 1983; Riley et al., 

2007; Warabi et al., 2005); however, there does not currently appear to be consensus as to what, 

if any, differences exist between the two. With respect to temporal-spatial variables, increased 

cadence and decreased stance time during treadmill walking appear to be the only consistent 

findings. Although statistically significant decreases in swing time (Lee and Hidler, 2008) and 

stride length (Pearce et al.) have also been reported, other researchers have found these 
2

differences to be either nonexistent or to show a trend in the opposite direction (Alton et al.; 

Murray et al.; Parvataneni et al.; Riley et al.). 

Of those studies evaluating overall sagittal plane joint excursions (Alton et al., 1998; Lee and 

Hidler, 2008; Parvataneni et al., 2009), no significant differences were observed, with the 

exception of one finding of increased hip ROM (Alton et al.) and one of decreased knee 

excursion (Lee and Hidler). A 3° to 4° increase in peak hip flexion was reported by both Alton 

et al. and Parvataneni et al., while Riley et al. (2007) found peak hip flexion to be reduced by 

<1°, and Lee and Hidler found no difference. Murray et al. (1985) and Riley et al. both reported 

a significant reduction in hip extension during treadmill walking; however, other researchers 

found no difference between the two conditions. Findings for peak knee angles appear to be 

more consistent across studies, with no difference found for peak flexion and two reports of 

small but significant decreases in peak extension values (Parvataneni et al.; Riley et al.) during 

treadmill walking. With the exception of one report of a 3° increase in dorsiflexion (Murray et 

al.), peak ankle angles have generally been reported to be similar between overground and 

treadmill walking (Alton et al.; Lee and Hidler; Parvataneni et al.; Riley et al.). Riley et al. and 

Lee and Hidler additionally evaluated differences in kinetics during overground and treadmill 

walking. A lack of difference in peak ankle power and significant decrease in peak knee 

extensor moment and braking ground reaction force were the only similar findings between the 

two studies. 

The effect of treadmill walking on muscle activity was investigated by Murray et al. (1985) and 

Lee and Hidler using two different mathematical methods. Murray et al. calculated the average 

electromyographic (EMG) signal over the entire gait cycle for several muscle groups and found 

activity in the quadriceps alone to be increased during the treadmill condition. In Lee and 

Hidler’s study, the gait cycle was broken into seven segments, and the integral of the EMG 

signal (iEMG) was calculated independently for each of those time periods. Similar to the 

findings of Murray et al., quadriceps activity during the last half of the gait cycle was higher on 

the treadmill. However, the iEMG of several other lower extremity muscles was also found to be 

significantly different on the treadmill at various points within the gait cycle. 

Finally, with respect to physiological differences, treadmill walking has been found to have no 

effect on heart rate (Murray et al., 1985) to increase it (Parvataneni et al., 2009) and decrease it 

(Pearce et al., 1983). Murray et al. and Pearce et al. additionally found no difference in oxygen 

consumption between the two conditions; however, Parvataneni and colleagues reported a 23% 

increase in metabolic cost during treadmill walking. 

1.3 Omni-Directional Treadmills 

The U.S. Army Research Laboratory-Human Research and Engineering Directorate (ARLHRED) evaluated the energy expenditure on the first-generation design of the ODT (Virtual 

Space Devices Inc., Bloomington, MI, figure 1). The design of the first-generation ODT 

employs two belts arranged perpendicularly, one inside the other (figure 1). The top belt consists 
3

Figure 1. First-generation ODT (a) and first-generation ODT belt configuration (b). 

of rollers that freely rotate perpendicular to the direction of travel of the belt. The rollers on the 

top belt rotate through contact with the lower moving belt. Therefore, the recentering movement 

of the user in one axis is caused by the rotation of the rollers, while movement in the other axis is 

caused by the travel of the top belt; both can occur simultaneously. This allows the user of the 

ODT to move in any direction while remaining within the 4- × 4-ft working surface. Another 

major difference between the ODT and conventional treadmills is that the speed at which the 

ODT’s belts move are in response to the movement of the user rather than being set to a constant 

value. For the energy expenditure evaluation, the participants traversed two different courses: a 

simulated course on the ODT where the environment was viewed on a head-mounted display 

(HMD) and a similar real-world indoor course. They traversed the courses at two different 

speeds and while carrying two different loads. Oxygen uptake, heart rate, and rating of 

perceived exertion (RPE) were measured and compared (Crowell et al., 2006). As expected, all 

three measures increased with increasing speed and load. All three measures were also higher on 

the first-generation ODT than on the real-world course. Oxygen uptake increased 17.8%, heart 

rate increased 8.6%, and RPE increased 25.6%. The researchers felt that the greater 

physiological demand to walk on the ODT may be caused by the users feeling unstable or 

unbalanced, causing them to activate more muscles to maintain stability. This may be due to 

problems with the control system misinterpreting the user’s upper body motions and initiating 

“false starts,” or overshooting the center resulting in repeated overcorrecting movements of the 

belts. Additionally, the control system did not allow the user to make sharp turns and fine 

movements easily. They also thought the reduced field of view (FOV) associated with the 

HMDs may have contributed to the users straying off the course and having to move faster to 

(a) (b) 
4

maintain the pace. Darken et al. (1997) performed a limited human factors evaluation of the 

ODT. Their findings were based on observations from videotapes of a single user performing a 

set of locomotion tasks on the ODT. They concluded that “users of the ODT must learn how to 

walk on the ODT,” and that it was readily apparent that the locomotion was not the same as the 

real world. 

Recommendations were made for improvements to the first-generation ODT, resulting in the 

Omni-Directional Treadmill Upgrade (MTS Systems Corp., Eden Prairie, MN, and Virtual Space 

Devices Inc., figure 2), which ARL-HRED received in September 2006. As opposed to the 

roller design used in the first-generation ODT, the ODT Upgrade incorporates a series of 80 

4-in-wide mini-belt segments attached perpendicularly to the underlying main belt (figure 2). 

The main belt travels in the x-axis. The mini-belts travel with the main belt but also operate like 

mini-treadmills to generate movement in the y-axis. The operation of the mini-belts (y-axis) and 

the main belt (x-axis) is controlled by two separate motors so they can move independently and 

simultaneously to recenter the user. Improvements were made to the control system of the ODT 

Upgrade by incorporating a washout algorithm and fuzzy logic systems (Hessburg and Clark, 

2005). The washout algorithm attempts to allow the users to feel the expected motion cues of 

their various gaits, while minimizing their perception of the movement needed to maintain their 

position in the workspace. The fuzzy logic is used to determine the gait of the user (i.e., walking 

forward, walking backward, etc.) and adjust the parameters of the washout algorithm 

accordingly. The size of the working surface was increased to 8 × 8 ft, which could enable a 

slower, less perceptible speed to return the user to the center. ARL-HRED has integrated the 

ODT Upgrade into a CAVE Automatic Virtual Environment with large rear projection screens 

for visually displaying the virtual environment. This provides a more natural FOV as opposed to 

the HMDs and permits users to see their feet. The noise levels produced by the ODT Upgrade 

are also lower than those produced by the first-generation ODT, which may be less distracting to 

users and allow them to better hear the sounds from the virtual environment. 

Figure 2. ODT Upgrade (a) and ODT Upgrade belt configuration (b). 

(a) (b)
5

1.4 Objective 

The ability of the ODT Upgrade to impose biomechanical and physiological effects on the user 

that are similar to those experienced in the real world is unknown. The purpose of this 

investigation was to determine whether walking on the ODT Upgrade is comparable to walking 

overground for selected biomechanical and physiological variables, quantify any significant 

differences, and determine if those differences are affected by walking speed. This was 

accomplished by using a within subjects 2 × 2 experimental design with two levels of terrain 

(ODT and overground) and two walking speeds (1.12 and 1.34 m•s-1). 

2. Materials and Methods 

2.1 Participants 

Six male and four female civilian employees of ARL-HRED volunteered to participate in this 

investigation (table 1). The participants read and signed a statement of informed consent* and 

self-reported that they were physically fit to complete the study protocol. Participants also 

completed a motion sickness questionnaire (appendix A) to obtain a baseline for comparison 

with symptom levels experienced during the study and at the conclusion of testing (Kennedy et 

al., 1992). 

Table 1. Participant characteristics. 

Participant Age 

(years) 

Mass 

(kg) 

Height 

(cm) 

Leg Length 

(cm) 

Males (n = 6) 42.2 (9.7) 86.3 (15.0) 179.2 (6.2) 96.4 (5.4) 

Females (n = 4) 38.0 (3.8) 61.3 (6.9) 163.8 (8.5) 89.4 (4.9) 

All (n = 10) 40.5 (7.8) 76.3 (17.6) 173.0 (10.4) 93.6 (6.1) 

Note: Values are group mean (standard deviation). 

2.2 Instrumentation 

2.2.1 Immersive Environment Simulator 

Located at Aberdeen Proving Ground, MD, the Immersive Environment Simulator (IES) 

(figure 3) consists of a second-generation ODT (ODT Upgrade, MTS Systems Corp., and Virtual 

Space Devices Inc.) integrated with a reconfigurable display system (RAVE II, Fakespace 

Systems, Kitchner, Ontario, Canada) and camera-based motion tracking system (Vicon Motion 

Systems, Inc., Lake Forest, CA). The 8- × 8-ft working surface of the ODT upgrade, made up of 

80 mini-belts that move perpendicularly to a main belt, allows the user to walk, jog, or even 

 *

 The investigators have adhered to the policies for the protection of human subjects as prescribed in AR 70-25 (1990). 
6

Figure 3. Immersive environment simulator.

crawl in any direction. Folding the four 12.5- × 10-ft rear-projected screens in at 90° to one 

another completely immerses users in the virtual environment and provides them with a full 360° 

FOV. Clusters of reflective markers attached to a helmet and a rigid plate on the back of a 

neoprene waistband are tracked in real-time by the Vicon system. The position and attitude of 

the helmet are used to determine the user’s eyepoint and adjust the perspective of the display 

accordingly, while the speed and heading of the rigid plate are used to determine how the belts of 

the ODT Upgrade should move to return the user to the center of the workspace. 

2.2.2 Three-Dimensional Motion Capture 

Temporal-spatial and kinematic variables during walking on the ODT Upgrade and overground 

were assessed using the 3-D trajectories of retroreflective markers attached to each participant’s 

pelvis, legs, and feet (figure 4). Individual tracking markers were placed bilaterally on the 

anterior superior iliac spines, anterior and lateral aspects of the thighs and shanks, lateral femoral 

condyles and malleoli, heels, and first metatarsophalangeal joints. A marker located at the 

middle of the bottom edge of the back belt used by the ODT Upgrade control system was aligned 

with the sacrum. For the purpose of defining the segments and their coordinate systems, 

anatomical markers were also placed over the medial femoral condyles and malleoli during a 

static standing trial and then removed for the walking trials. During the ODT Upgrade trials, 

marker trajectories were recorded and tracked using a Vicon Peak 460 motion capture system 

(Vicon Motion Systems, Inc.) consisting of six M2 cameras and Workstation 5.2.4 software. For 

the overground trials, six Falcon cameras and EVaRT 4.0 software (Motion Analysis 

Corporation, Santa Rosa, CA) were used. In order to reduce any potential issues associated with 

using two different systems, all data for a given participant were collected within a single session 

(i.e., identical marker set for all trials), and both systems were fully calibrated prior to each data 

collection session. Motion capture data were collected at a sampling rate of 60 Hz 

approximately every 45 s for 10 s throughout each trial. 
7

Figure 4. Placement of tracking and 

anatomical markers. 

2.2.3 Physiological Demand Assessment 

Oxygen consumption was measured using a K4b2 portable cardiopulmonary exercise testing 

system (Cosmed USA, Chicago, IL) and its associated software. The K4b2

 system collects and 

samples exhaled gases breath-by-breath using a facemask and small-diameter tubing connected 

to the main unit, which is positioned on the participant’s chest along with the battery pack 

(figure 5). O2 and CO2 concentrations of the expired gases were stored to the main unit 

throughout each walking trial and then downloaded to the Cosmed software for further analysis. 
8

Figure 5. The participant wears a 

facemask and Cosmed K4b2

. 

2.3 Data Collection Protocol 

Data were collected while participants walked at ~1.12 m•s-1 (2.5 mph) and 1.34 m•s-1 (3.0 mph) 

on the ODT Upgrade and overground for 5-min periods. The order in which the conditions were 

presented to the participants was counterbalanced to minimize learning and fatigue effects. For 

the overground trials, the participants walked along a circular path with a radius of 14 ft 

(figure 6a) while following an investigator pushing a pacing wheel at the appropriate speed. For 

the ODT Upgrade trials, a model of the room in which the overground trials occurred containing 

a dimensionally identical circular course was displayed on the RAVE II screens. The 

monoscopic display was at a resolution of 1280 ×1024 and a frame rate of 60 Hz. An avatar 

moved along the course in front of the participants to help them maintain the appropriate speed 

(figure 6b). 

Figure 6. The participant follows an investigator during the overground trials (a) and a virtual 3 entity 

during ODT Upgrade trials (b).

(a) (b) 
9

Prior to beginning the data collection session, the participants were given an opportunity to 

practice walking on the ODT Upgrade. They were first fitted with a safety harness, helmet, and 

neoprene belt. Next, an investigator familiarized participants with the operation of the device 

and all of the safety and emergency stopping procedures available to them and the operator. The 

participants were then allowed to walk in all directions on the ODT Upgrade until they felt 

comfortable doing so and appeared to have no hesitation or issues with their balance. Once 

comfortable operating the ODT Upgrade, the participants practiced following the avatar along 

the circular course in the virtual environment until they were capable of consistently maintaining 

the correct pace. The participants typically required less than a half hour to become proficient at 

negotiating the course. 

Following the participants’ training session, reflective tracking markers were applied to their 

hips, legs, and feet, as previously described. The participants were then fitted with a facemask 

and heart rate monitor chest strap and donned the K4b2 unit. Once all equipment was in place, 

the participants were given an opportunity to acclimate themselves with breathing into the 

facemask. Next, static calibration trials were collected in both the ODT Upgrade and overground 

motion capture volumes, followed by removal of the medial knee and ankle markers. Finally, 

the participants began the first of their 5-min data collection trials. Participants were given a 

minimum 10-min break between trials to allow their heart rate and energy expenditure to return 

to baseline values. During each break, the participants also provided an RPE for the trial they 

had just completed using the Borg scale (appendix B). 

After completion of the data collection trials, participants were asked again to fill out the motion 

sickness questionnaire shown in appendix A. If any of the motion sickness symptoms were 

elevated from those reported prior to the start of the trials, participants were asked to rest quietly. 

The questionnaire was then repeated every 15 min until the symptoms subsided, at which time, 

participants were released from the study. 

2.4 Data Reduction and Analysis 

Reflective marker trajectories were reconstructed and labeled in either Workstation (ODT 

Upgrade) or EvaRT (overground) and then exported to c3d files. Oxygen consumption (mL 

O2•min-1) data were exported from the Cosmed software into tab-delimited text files. As 

described next, the remainder of the signal processing and data reduction was performed using a 

series of custom programs written in LabVIEW 8.2 (National Instruments, Austin, TX). 

The tracked reflective marker data were first smoothed at a cutoff frequency of 6 Hz using a 

fourth-order, zero-lag, low-pass Butterworth filter. Due to the lack of ground reaction force data, 

heel strike (HS) and toe-off (TO) events were determined using a velocity-based algorithm (Zeni 

et al., 2008) applied to the heel marker trajectories in the pelvic coordinate system. HS was 

defined as the time at which the anterior-posterior component of the heel marker velocity 

transitioned from positive to negative, and TO was defined as the time at which the anteriorposterior component of the toe marker velocity transitioned from negative to positive. 
10

Several temporal-spatial parameters were then calculated bilaterally for each gait cycle: stance 

time (TO-HS), swing time (HS-TO), toe-off (stance time/[stance time + swing time] × 100), 

cadence (120/[stance time + swing time]), and walking speed ([stride length × cadence]/120). 

Due to the manner in which the ODT Upgrade operates and the fact that the participants were 

walking on a slight curve in both environments, stride length was calculated as the sum of the 

anterior-posterior excursion of the heel marker with respect to the pelvic coordinate system from 

HS to TO and from TO to HS. To account for differences in stature and leg length between 

participants, stride length and cadence were additionally normalized using the following 

equations (Hof, 2006): 

 stride lengthnorm = stride length/l , (1) 

and 

 cadencenorm = cadence ൈ ට݈

ൗ݃ , (2) 

where l is the participant’s leg length in meters (calculated from the vertical position of the 

participant’s hip joint center in the static trial) and g is 9.81 m•s-2. 

Sagittal plane Euler joint angles were also calculated for the hips, knees, and ankles and time 

normalized to 100 points over each gait cycle. The similarity of each participant’s mean joint 

angle curves from the ODT Upgrade trials as compared to the overground trials was determined 

from four measures: trend normalcy, range amplitude ratio, range offset, and phase offset. The 

methodology behind the calculation of these measures is described in detail by Crenshaw and 

Richards (2006) and summarized here. Trend normalcy represents similarity in the shape of two 

curves independent of any differences in their magnitude. It is determined from the ratio of 

variability about and along an eigenvector calculated from the singular value decomposition of a 

square matrix formed by multiplying the transpose of a matrix containing both waveforms by 

itself (MT

M). As presented here, a trend normalcy value of 1 indicates that the two curves are 

identical in shape. Range amplitude ratio compares the overall range of motion (ROM, max 

value – min value) of the two curves and is simply calculated by dividing the ROM of the curve 

of interest (i.e., ODT Upgrade) by that of the normative curve (i.e., overground). Therefore, a 

range amplitude ratio of 1 indicates no difference in ROM, while a value >1 indicates a larger 

ROM, and a value <1 indicates a smaller ROM for the curve of interest, compared to the 

normative curve. Subtracting the mean value of the normative curve from that of the curve of 

interest gives us the range offset. A positive value indicates a more flexed operating range for 

the curve of interest, while a negative value indicates more extension compared to the normative 

curve. Finally, phase offset is the percentage of the gait cycle that the curve of interest must be 

shifted by in order to maximize trend normalcy. A positive value indicates that the curve of 

interest must be shifted to the right, while a negative value indicates that shift to the left is 

required. 
11

Raw oxygen consumption data were first normalized to the participant’s body mass. Mean 

normalized oxygen consumption was then calculated over the last minute of data from each trial. 

2.5 Statistical Analyses 

The design of this study is within subjects with two independent variables, each having two 

levels: terrain (ODT Upgrade and overground) and walking speed (1.12 and 1.34 m•s-1). 

Descriptive statistics were calculated for participant characteristics, RPE responses, and all other 

variables of interest. Due to the course being circular rather than straight, values for the left and 

right legs were analyzed separately. An overall significance level of 0.05 was used for all 

comparisons. 

A multivariate analysis of variance with post hoc analyses of significant results was used to 

assess the main effect of terrain on the temporal-spatial measures at each walking speed. With 

respect to sagittal plane joint angles, 95% confidence intervals were first determined for trend 

normalcy, phase offset, range amplitude ratio, and range offset of joint angles during overground 

walking by analyzing the individual curves for each participant with respect to the group mean at 

each walking speed. Each participant’s mean joint angle curves from the ODT Upgrade 

conditions were then analyzed for normalcy in comparison to the group mean curves from the 

overground conditions. Those falling outside of the 95% confidence intervals were identified. 

Finally, the effect of terrain on normalized oxygen consumption and on RPE at each walking 

speed was individually assessed using paired t-tests. 

3. Results 

3.1 Temporal-spatial 

Left and right temporal-spatial parameter values during walking overground and on the ODT are 

shown in table 2. As previously described, cadence and stride length are normalized and 

therefore nondimensional. While slightly higher than the target values for each walking speed 

condition, the calculated speeds were not significantly different between terrain conditions. 

Terrain condition was found to have a significant main effect (p = 0.038), only at the faster 

walking speed. Left and right swing time (p = 0.011 and 0.024) and left stride length (p = 0.029) 

were significantly shorter during walking on the ODT than overground at 1.34 m•s-1. As a 

consequence of the decreased left stride length, cadence for the left leg was significantly greater 

on the ODT (p = 0.006). 
12

Table 2. Temporal-spatial parameters.

Parameter 

1.12 m/s (2.5 mph) 1.34 m/s (3.0 mph) a

Overground ODT Overground ODT 

Speed (m/s) Left 1.27 (0.08) 1.27 (0.08) 1.45 (0.10) 1.44 (0.15) 

Right 1.22 (0.08) 1.23 (0.11) 1.40 (0.10) 1.42 (0.17) 

Cadence Left 35.7 (0.6) 37.7 (3.2) 37.2 (1.3) 39.8 (2.4) b

Right 33.5 (1.9) 34.6 (2.7) 35.3 (2.1) 37.4 (2.8) 

Stance time (s) Left 0.74 (0.03) 0.72 (0.05) 0.69 (0.03) 0.65 (0.05) 

Right 0.75 (0.03) 0.72 (0.04) 0.69 (0.03) 0.65 (0.05) 

Swing time (s) Left 0.39 (0.02) 0.37 (0.03) 0.38 (0.02) 0.35 (0.02) b

Right 0.39 (0.01) 0.37 (0.03) 0.38 (0.02) 0.35 (0.03) b

Stride length Left 1.45 (0.09) 1.38 (0.12) 1.54 (0.07) 1.43 (0.12) b

Right 1.39 (0.08) 1.35 (0.16) 1.48 (0.07) 1.42 (0.14) 

Toe-off (% cycle) Left 65.4 (0.9) 65.8 (0.4) 64.6 (0.8) 65.2 (0.8) 

Right 65.6 (0.6) 66.0 (0.8) 64.5 (0.6) 64.8 (0.9) 

Note: Values are group mean (standard deviation). 

a

 Main effect of terrain. 

b

 Significantly different from overground condition. 

3.2 Kinematics

Mean sagittal plane hip, knee, and ankle joint angles during walking overground and on the ODT 

at 1.12 and 1.34 m/s are presented in figures 7 and 8, respectively. The trend normalcy, range 

amplitude, range offset, and phase offset values resulting from the comparison of the ODT joint 

angle curves to those obtained during overground walking can be found in table 3, along with the 

95% confidence intervals for each parameter. 

The general shape of the joint angle curves for the ODT condition is quite similar to those for the 

overground condition during walking at both speeds. Only the right ankle produced a trend 

normalcy value that was substantially outside of the 95% confidence interval for overground 

walking. The overall sagittal plane range of motion at the hip and knee are also comparable 

between the two terrain conditions (i.e., range amplitude near 1). At the ankle, however, the 

range amplitude ratio is between 0.78 and 0.85, indicating a roughly 20% reduction in ankle 

ROM during walking on the ODT. The majority of this difference appears to be due to a 

decrease in the amount of plantarflexion achieved immediately following toe-off (figures 7 

and 8). The greatest difference between the kinematics for the two terrain conditions is in the 

overall amount of flexion at all three joints. Both hips, both knees, and the right ankle are up to 

5% more flexed throughout the entire cycle of walking on the ODT than overground. 
13

Figure 7. Mean sagittal plane hip, knee, and joint angles during walking at 1.12 m/s overground and on the ODT. Shaded area repr

deviation above and below the overground mean. 

overground ODT 

Right Left 

 Hip Knee A
14

Figure 8. Mean sagittal plane hip, knee, and joint angles during walking at 1.34 m/s overground and on the ODT. Shaded area represent

and below the overground mean. 

overground ODT 

Right Left 

 Hip Knee Ankle 
15 

Table 3. Sagittal plane joint angle normalcy during walking on the ODT.

Parameter 

1.12 m/s (2.5 mph) 1.34 m/s (3.0 mph) 

Mean (standard 

deviation) 95% CIa Mean (standard 

deviation) 95% CIa

Hip 

Trend normalcy Left 0.998 (0.001) 0.996, 1 0.998 (0.001) 0.996, 1 

Right 0.997 (0.002) 0.995, 1 0.997 (0.002) 0.997, 1 

Range amplitude 

(ODT/OG) 

Left 0.99 (0.03) 0.95, 1.06 0.97 (0.05) 0.97, 1.06 

Right 0.99 (0.08) 0.97, 1.06 1.01 (0.06) 0.97, 1.07 

Range offset 

(degrees) 

Left 3.46 (2.11) –1.66, 1.66 4.50 (3.00) –1.71, 1.71 

Right 3.75 (3.08) –1.95, 1.95 3.52 (1.86) –1.80, 1.80 

Phase offset 

(% gait cycle) 

Left 0.20 (0.8) –0.61, 0.81 0.40 (0.52) –0.58, 0.58 

Right –0.10 (0.57) –0.61, 0.81 0.20 (0.79) –0.30, 0.50 

Knee 

Trend normalcy Left 0.992 (0.007) 0.992, 1 0.994 (0.004) 0.992, 1 

Right 0.992 (0.006) 0.993, 1 0.989 (0.010) 0.993, 1 

Range amplitude 

(ODT/OG) 

Left 0.96 (0.03) 0.97, 1.04 0.96 (0.05) 0.97, 1.00 

Right 1.00 (0.07) 0.97, 1.04 1.01 (0.06) 0.98, 1.03 

Range offset 

(degrees) 

Left 3.84 (2.45) –2.55, 2.55 4.86 (3.14) –2.60, 2.60 

Right 4.53 (3.89) –2.44, 2.44 4.47 (3.56) –2.60, 2.60 

Phase offset 

(% gait cycle) 

Left –0.40 (0.52) –0.31, 0.51 –0.20 (0.42) –0.31, 0.51 

Right –0.40 (0.84) –0.36, 0.76 –0.50 (0.97) –0.48, 0.48 

Ankle 

Trend normalcy Left 0.980 (0.024) 0.953, 1 0.978 (0.021) 0.943, 1 

Right 0.952 (0.047) 0.979, 1 0.946 (0.081) 0.974, 1 

Range amplitude 

(ODT/OG) 

Left 0.82 (0.11) 0.89, 1.13 0.78 (0.14) 0.89, 1.14 

Right 0.85 (0.08) 0.89, 1.12 0.78 (0.14) 0.89, 1.14 

Range offset 

(degrees) 

Left 0.84 (3.28) –1.39, 1.39 1.04 (3.76) –1.64, 1.64 

Right 4.49 (5.89) –2.18, 2.18 3.22 (2.53) –2.19, 2.19 

Phase offset 

(% gait cycle) 

Left 0.40 (1.58) –1.08, 0.88 0.90 (1.20) –1.26, 1.26 

Right 0.30 (2.11) –0.63, 0.43 0.40 (1.90) –0.73, 0.53 

Note: Bolded items are outside of the 95% confidence interval for overground walking. 

a

CI = Confidence Interval. 

3.3 Metabolic Cost 

Normalized steady-state oxygen consumption values during walking overground and on the 

ODT are presented in figure 9. At both speeds, the metabolic cost of walking on the ODT was 

more than 20% greater than walking at the same speed overground. Additionally, oxygen 

consumption during walking on the ODT at 1.12 m•s-1 appears to be roughly equivalent to 

walking 0.2 m•s-1 (0.5 mph) faster overground. 
16 

Figure 9. Metabolic cost during walking overground and on the ODT. 

3.4 Ratings of Perceived Exertion 

RPE values were significantly higher for walking on the ODT Upgrade at both 1.12 m•s-1

(p = 0.003) and 1.34 m•s-1 (p = 0.000). At the slower speed, both terrain conditions received 

ratings roughly equal to “very light” (overground = 8.5 ± 1.4 and ODT = 9.3 ± 1.4). The gap in 

perceived exertion levels between the two conditions widened at the faster speed, with the RPE 

for walking overground remaining near “very light” (8.6 ± 1.2) and that of the ODT Upgrade 

approaching a rating of “light” (10.2 ± 1.9). 

3.5 Motion Sickness Questionnaire Response 

Four of the participants reported slightly elevated symptoms after completing their trials. All 

four reported slight feelings of fatigue, two reported slight sweating, and one reported a slight 

headache. The fatigue and sweating may have been caused by the physical activity involved in 

the trials. However, as per the protocol, all four participants rested quietly for 15 min, after 

which they reported that the symptoms had subsided, and they were released from the study. 

Three other participants had symptoms that they reported as slight prior to the trials, which were 

decreased to none after the trials. Three participants reported no symptoms before or after. 

10.7

12.3

12.9

15.2

0

2

4

6

8

10

12

14

16

18

20

1.12 m/s 1.34 m/s

normalized VO2, ml/min/kg

Overground

ODT

p=0.013

p=0.006
17 

4. Discussion 

Incorporating the effects of realistic physical workload from traversing terrain (spatial 

relationships, fatigue, psychomotor control, etc.) into dismounted Soldier simulators and 

enhancing their psychosomatic immersion into the environment may increase the efficacy of the 

training effects and research results. The integration of the ODT Upgrade into a dynamic and 

visually immersive environment may provide for realistic, high-fidelity dismounted warrior 

simulations that will enable repeatable, laboratory-controlled mission rehearsal and 

investigations of critical Soldier issues. Additionally, this permits multisensory immersion of 

Soldiers into an environment that may vary from benign to hostile without exposing them to the 

hazards and variability of outdoor experimentation. However, the effectiveness of such 

simulations is dependent on the system’s ability to impose biomechanical and physiological 

effects on the user that are similar to those experienced in the real world. The purpose of this 

investigation was to determine the extent to which the ODT Upgrade incorporated into the IES is 

capable of doing so. These findings indicate that while the ODT Upgrade permits the user to 

walk through a virtual environment in a relatively natural way, physiological demand is 

significantly increased. 

In the present study, the gait mechanics associated with walking on the ODT Upgrade are, in 

general, comparable to those of overground walking. Cadence was found to be increased on the 

ODT, although only significantly so at the faster walking speed. While not statistically 

significant, there was also a tendency for stance time to be shorter during the ODT condition at 

both speeds. These findings are consistent with those of previous studies involving conventional 

treadmills. Similar to the respective findings of Lee and Hidler (2008) and Pearce et al. (1983), 

swing time and stride length were also observed to be shorter during walking on the ODT 

Upgrade. With the exception of an overall trend of increased flexion, there was little apparent 

difference in the hip and knee joint angle patterns between walking on the ODT Upgrade and 

overground (table 3). However, at the ankle, total range of motion was decreased bilaterally by 

~20% during the ODT Upgrade conditions. Additionally, the right ankle achieved about 10° less 

peak plantarflexion immediately following toe-off. The increase in peak flexion and decrease in 

peak extension values at the hip and knee are consistent with the findings of other researchers, 

but neither the significant reduction in ankle ROM or peak plantarflexion angle have been 

previously reported for walking on conventional treadmills. 

It has been suggested that the observed differences in gait mechanics of walking overground and 

on a conventional treadmill might be related to an attempt to keep up with the speed of the 

treadmill belt and avoid falling off the back of the deck (Alton et al., 1998; Murray et al., 1985) 

or due to an altered sense of balance and stability resulting from differences in optic flow (Lee 

and Hidler, 2008). Considering that the belt speed of the ODT Upgrade is dependent on the 
18 

user’s own movement and that the control system is always working to move the user away from 

the edges and return the user to the center of the active surface, it is unlikely that a sense of 

urgency or fear of falling off the edge of the ODT Upgrade were responsible for the observed 

increase in cadence and decrease in stride length. Incorporation of the CAVE system with the 

ODT Upgrade allowed participants to be fully immersed in the virtual environment, thus 

minimizing any differences in optic flow between the two terrain conditions. Therefore, it also 

seems unlikely that optic flow differences contributed to the observed disparities in gait 

mechanics in this study. It is probable, however, that the increased cadence, decreased swing 

time, decreased stride length, and overall increased joint flexion on the ODT Upgrade are related 

to an attempt by the central nervous system to increase stability. Reducing the duration of the 

swing phase could result in an increased period of double-support that would, in turn, mean less 

time spent on a potentially unstable single limb (Marigold and Patla, 2002; Murray et al., 1985). 

In theory, adopting a more flexed posture should also lower the participant’s center of gravity 

toward his or her base of support, effectively increasing stability. This is similar to what people 

tend to do when knowingly traversing slippery terrain (Marigold and Patla). 

Despite minimal differences in temporal-spatial values and kinematics for the two terrain 

conditions, there is a substantially higher rate (>20%) of oxygen consumption associated with 

walking on the ODT Upgrade. This is higher than the 17.8% increase measured on the first 

generation ODT; however, that difference is likely due to the slower walking speeds (0.67 and 

1.12 m•s-1) used in the previous evaluation. In the present study, the difference in oxygen 

consumption between the two terrain conditions increased ~3%, with an increase in walking 

speed from 1.12 to 1.34 m•s-1. 

Although the differences in cadence between the two terrain conditions were small, they may 

still be worth noting considering that for a given walking speed, cadence is generally consistent 

within an individual (Murray et al., 1985). In a study by Umberger and Martin (2007), a 10% 

increase in stride rate at a fixed walking speed resulted in a nearly equal increase in energy 

expenditure. Therefore, it seems plausible that the 5% to 7% increase in cadence during walking 

on the ODT Upgrade may, in part, contribute to the substantially greater metabolic cost. Some 

potential sources of the remaining increase in physiological demand are differences in 

mechanical power, muscle activity, and arm swing. 

Increased cadence at a fixed walking speed has been found to increase the mechanical work 

performed by the lower extremities (Cavagna and Franzetti, 1986; Umberger and Martin, 2007). 

It is also probable that the reduction in overall ankle range of motion and peak plantarflexion at 

push-off during the ODT Upgrade trials has implications on power generation at the ankle that 

would need to be compensated for at the hip and knee. Fixation of the ankle during walking at a 

set speed has been shown to increase metabolic cost by up to 15% (Vanderpool et al., 2008). 

Therefore, evaluation of the total and segmental work performed during walking on the ODT 
19 

Upgrade as compared to overground would likely provide more insight into how those 

differences in gait mechanics affect the energetics associated with each terrain condition. In this 

investigation, participants typically maintained a more flexed leg position throughout the gait 

cycle, theoretically requiring greater activation of the flexors at each joint. If the differences in 

gait mechanics between the two conditions are, in fact, reflective of an attempt by the central 

nervous system to improve balance and stability, then an increase in coactivation of antagonist 

muscles also seems likely. Both of these scenarios would consequently increase metabolic cost. 

Arm swing during walking is believed to help regulate whole-body angular momentum by 

counteracting pelvic rotation (Ballesteros et al., 1965; Elftman, 1939; Herr and Popovic, 2008). 

It has been suggested that minimizing moments about the center of mass through controlled arm 

movements results in a smoother and more efficient gait (Eke-Okoro et al., 1997; Herr and 

Popovic). Additionally, Umberger (2008) reported that restriction of arm swing during walking 

increases gross energy expenditure by up to 5%. Although not quantified in this study, it was 

observed that several of the participants tended to hold their arms rigidly by their sides during the 

ODT Upgrade conditions rather than allowing them to swing naturally as they did overground. It 

seems likely that a portion of the increased metabolic demand during walking on the ODT 

Upgrade may be associated with a reduction in arm swing. There also appears to be a reciprocal 

relationship between arm swing and stride length (Eke-Okoro et al.), which could explain the 

reduction in stride length observed on the ODT Upgrade. 

Perceived exertion levels for walking on the ODT Upgrade were higher than those for walking at 

the same speed overground. This result is not really surprising given the substantial increase in 

physiological demand associated with walking on the ODT Upgrade. Some participants reported 

that they felt they were walking faster during the ODT trials than overground, even though in 

actuality, the speeds were identical. Additionally, several participants commented that it was 

more difficult to stay on course when following the avatar in the virtual environment, especially 

at the faster speed. This could be partly due to the lack of visual information from the virtual 

environment on the ODT Upgrade surface. There is no projected image on the walking surface; 

therefore, the participants cannot see where their footsteps are occurring in the environment. The 

ground level of the virtual environment is only visible on the screens 3–4 ft out from the user’s 

position. It could also be caused in part by the monoscopic displays, which provide no cues for 

depth perception. These factors may have additionally contributed to their increased RPE scores 

for the ODT Upgrade condition. 
20 

5. Conclusions 

In conclusion, the ODT Upgrade permits the user to walk through a virtual environment in a 

natural way but with a significant increase in metabolic cost and perception of physical exertion. 

These differences must be taken into account when comparing the results of training or research 

studies using the ODT Upgrade to those of real-world activities. Future studies should seek to 

identify and develop a better understanding of the underlying causes for increased physiological 

demand associated with walking on the ODT Upgrade. This could aid in devising improvements 

to the control system or determining more optimal design characteristics for future mobility 

platforms to more closely match real-world physiological demands. The possibility of training 

individuals to walk on the ODT Upgrade in a more energetically efficient manner should also be 

explored. 
21 

6. References 

Alton, F.; Baldey, L.; Caplan, S.; Morrissey, M. C. A Kinematic Comparison of Over-Ground 

and Treadmill Walking. Clin. Biomech. 1998, 13, 434–440. 

AR 70-25. Use of Volunteers as Subjects of Research; Headquarters, U.S. Department of the 

Army,Washington, DC, 1990. 

Ballesteros, M. L.; Buchthal, F.; Rosenfalck, P. The Pattern of Muscular Activity During the 

Arm Swing of Natural Walking. Acta. Physiol. Scand. 1965, 63, 296–310. 

Cavagna, G. A.; Franzetti, P. The Determinants of the Step Frequency in Walking in Humans. 

J. Physiol. 1986, 373, 235–242. 

Crenshaw, S. J.; Richards, J. G. A Method for Analyzing Joint Symmetry and Normalcy With 

an Application to Analyzing Gait. Gait Posture 2006, 24, 515–521. 

Crowell, H. P.; Faughn, J.; Tran, P. K.; Wiley, P. W. Improvements in the Omni-directional 

Treadmill: Summary Report and Recommendations for Future Development; ARL-TR3958; U.S. Army Research Laboratory: Aberdeen Proving Ground, MD, 2006. 

Darken, R. P.; Cockayne, W. R.; Carmein, D. The Omni-Directional Treadmill: A Locomotion 

Device for Virtual Worlds. Proceedings of UIST 97, 1997; pp 213–221. 

Eke-Okoro, S. T.; Gregoric, M.; Larsson, L. E. Alterations in Gait Resulting From Deliberate 

Changes of arm-Swing Amplitude and Phase. Clin. Biomech. 1997, 12 (7/8), 516–521. 

Elftman, H. The Function of the Arms in Walking. Human Biology 1939, 11, 529–535. 

Herr, H.; Popovic, M. Angular Momentum in Human Walking. J. Exp. Biol. 2008, 211, 

467–481. 

Hessburg, T. M.; Clark, A. J. Intelligent Control of a Planar Treadmill Ambulatory Simulator. 

Proceedings of ANNIE 2005 Conference, 2005. 

Hof, A. L. Scaling Gait Data to Body Size. Gait Posture 2006, 4, 222–223. 

Kennedy, R. S.; Lane, N. E.; Lilienthal, M. G.; Berbaum, K. S.; Hettinger, L. J. Profile Analysis 

of Simulator Sickness Symptoms: Application to Virtual Environment Systems. Presence

1992, 1 (3), 295–370. 

Lee, S. J.; Hidler, J. Biomechanics of Overground Versus Treadmill Walking in Healthy 

Individuals. J. Appl. Physiol. 2008, 104, 747–755.
22 

Marigold, D. S.; Patla, A. E. Strategies for Dynamic Stability During Locomotion on a Slippery 

Surface: Effects of Prior Experience and Knowledge. J. Neurophysiol. 2002, 88, 339–353. 

Murray, M .P.; Spurr, G. B.; Sepic, S. B.; Gardner, G. M.; Mollinger, L. A. Treadmill vs. Floor 

Walking: Kinematics, Electromyogram and Heart Rate. J. Appl. Physiol. 1985, 59 (1), 

87–91. 

Parvataneni, K.; Ploeg, L.; Olney, S. J.; Brouwer, B. Kinematic, Kinetic and Metabolic 

Parameters of Treadmill Versus Overground Walking in Healthy Older Adults. Clin. 

Biomech. 2009, 24, 95–100. 

Pearce, M. E.; Cunningham, D. A.; Donner, A. P.; Rechnitzer, P. A.; Fullerton, G. M.; Howard, 

J. H. Energy Cost of Treadmill and Floor Walking at Self-Selected Paces. Eur. J. Appl. 

Physiol. 1983, 52, 115–119. 

Riley, P. O.; Paolini, G.; Croce, U. D.; Paylo, K. W.; Kerrigan, D. C. A Kinematic Comparison 

of Over-Ground and Treadmill Walking in Healthy Patients. Gait Posture 2007, 26 (1), 

17–24. 

Umberger, B. R. Effects of Suppressing Arm Swing on Kinematics, Kinetics, and Energetics of 

Human Walking. J. Biomech. 2008, 41, 2575–2580. 

Umberger, B. R.; Martin, P. E. Mechanical Power and Efficiency of Level Walking With 

Different Stride Rates. J. Exp. Biol. 2007, 210, 3255–3265. 

Vanderpool, M. T.; Collins, S. H.; Kuo, A. D. Ankle Fixation Need Not Increase the Energetic 

Cost of Human Walking. Gait Posture 2008, 28, 427–433. 

Warabi, T.; Masamichi, K.; Kiriyama, K.; Yoshida, T.; Kobayashi, N. Treadmill Walking and 

Overground Walking of Human Subjects Compared by Recording Sole-Floor Reaction 

Force. Neurosci. Res. 2005, 53, 343–348. 

Zeni Jr., J. A.; Richards, J. G.; Higginson, J. S. Two Simple Methods for Detemining Gait 

Events During Treadmill and Overground Walking Using Kinematic Data. Gait Posture

2008, 27, 710–714. 
23 

Appendix A. Motion Sickness Questionnaire

 

 This appendix appears in its original form without editorial change. 
24 

Participant ID________________Date__________________Condition______________ 

Estimating Motion Sickness Questionnaire 

Please rate the following measure of motion sickness for the trial performed (or right now) by circling the 

word that best describes your feelings:

General Discomfort None Slight Moderate Severe 

Fatigue None Slight Moderate Severe 

Headache None Slight Moderate Severe 

Eyestrain None Slight Moderate Severe 

Difficulty Focusing None Slight Moderate Severe 

Increased Salivation None Slight Moderate Severe 

Sweating None Slight Moderate Severe 

Nausea None Slight Moderate Severe 

Difficulty Concentrating None Slight Moderate Severe 

Fullness of Head None Slight Moderate Severe 

Blurred Vision None Slight Moderate Severe 

Dizzy (eyes open) None Slight Moderate Severe 

Dizzy (eyes closed) None Slight Moderate Severe 

Vertigo* None Slight Moderate Severe 

Stomach Awareness** None Slight Moderate Severe 

Burping None Slight Moderate Severe 

* Vertigo is experienced as a loss of orientation with respect to vertical upright. 

** Stomach awareness is usually used to indicate a feeling of discomfort which is just short of nausea.
25 

Appendix B. Borg Scale

 

 This appendix appears in its original form without editorial change. 
26 

How to Use the Perceived Exertion Scale 

While doing physical activity, we want you to rate your perception of exertion. This feeling should reflect 

how heavy and strenuous the exercise feels to you, combining all sensations and feelings of physical 

stress, effort, and fatigue. Do not concern yourself with any one factor such as leg pain or shortness of 

breath, but try to focus on your total feeling of exertion. 

Look at the rating scale below while you are engaging in an activity; it ranges from 6 to 20, where 6 

means "no exertion at all" and 20 means "maximal exertion." Choose the number from below that best 

describes your level of exertion. This will give you a good idea of the intensity level of your activity, and 

you can use this information to speed up or slow down your movements to reach your desired range. 

Try to appraise your feeling of exertion as honestly as possible, without thinking about what the actual 

physical load is. Your own feeling of effort and exertion is important, not how it compares to other 

people's. Look at the scales and the expressions and then give a number. 

6 No exertion at all 

7 Extremely light 

8 

9 Very light - (easy walking slowly at a comfortable pace) 

10 

11 Light 

12 

 

13 Somewhat hard (It is quite an effort; you feel tired but can continue) 

14 

15 Hard (heavy) 

 

16 

17 Very hard (very strenuous, and you are very fatigued) 

18 

19 Extremely hard (You can not continue for long at this pace) 

20 Maximal exertion 
NO. OF 

COPIES ORGANIZATION 

27 

 1 DEFENSE TECHNICAL 

 (PDF INFORMATION CTR 

 only) DTIC OCA 

 8725 JOHN J KINGMAN RD 

 STE 0944 

 FORT BELVOIR VA 22060-6218 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 IMNE ALC HRR 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 RDRL CIM L 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 RDRL CIM P 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

 1 DIRECTOR 

 US ARMY RESEARCH LAB 

 RDRL D 

 2800 POWDER MILL RD 

 ADELPHI MD 20783-1197 

ABERDEEN PROVING GROUND

 1 DIR USARL 

 RDRL CIM G (BLDG 4600) 
NO. OF NO. OF 

COPIES ORGANIZATION COPIES ORGANIZATION

28 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM A J MARTIN 

 MYER CENTER BLDG 2700 RM 2D311 

 FORT MONMOUTH NJ 07703-5601 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM C A DAVISON 

 320 MANSCEN LOOP STE 115 

 FORT LEONARD WOOD MO 65473 

 2 ARMY RSCH LABORATORY – HRED 

 RDRL HRM DI 

 T DAVIS 

 J HANSBERGER 

 BLDG 5400 RM C242 

 REDSTONE ARSENAL AL 35898-7290 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRS EA DR V J RICE 

 BLDG 4011 RM 217 

 1750 GREELEY RD 

 FORT SAM HOUSTON TX 78234-5002 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM DG K GUNN 

 BLDG 333 

 PICATINNY ARSENAL NJ 07806-5000 

 1 ARMY RSCH LABORATORY – HRED 

 ARMC FIELD ELEMENT 

 RDRL HRM CH C BURNS 

 THIRD AVE BLDG 1467B RM 336 

 FORT KNOX KY 40121 

 1 ARMY RSCH LABORATORY – HRED 

 AWC FIELD ELEMENT 

 RDRL HRM DJ D DURBIN 

 BLDG 4506 (DCD) RM 107 

 FORT RUCKER AL 36362-5000 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM CK J REINHART 

 10125 KINGMAN RD BLDG 317 

 FORT BELVOIR VA 22060-5828 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM AY M BARNES 

 2520 HEALY AVE 

 STE 1172 BLDG 51005 

 FORT HUACHUCA AZ 85613-7069 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HR MP D UNGVARSKY 

 POPE HALL BLDG 470 

 BCBL 806 HARRISON DR 

 FORT LEAVENWORTH KS 66027-2302 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM DQ M R FLETCHER 

 NATICK SOLDIER CTR 

 AMSRD NSC WS E BLDG 3 RM 343 

 NATICK MA 01760-5020 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM AT J CHEN 

 12350 RESEARCH PKWY 

 ORLANDO FL 32826-3276 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM AT C KORTENHAUS 

 12350 RESEARCH PKWY 

 ORLANDO FL 32826 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM AS C MANASCO 

 SIGNAL TOWERS 

 BLDG 29808A RM 303A 

 FORT GORDON GA 30905-5233 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM CU 

 6501 E 11 MILE RD MS 284 

 BLDG 200A 2ND FL RM 2104 

 WARREN MI 48397-5000 

 1 ARMY RSCH LABORATORY – HRED 

 FIRES CTR OF EXCELLENCE 

 FIELD ELEMENT 

 RDRL HRM AF C HERNANDEZ 

 3040 NW AUSTIN RD RM 221 

 FORT SILL OK 73503-9043 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM AV S MIDDLEBROOKS 

 91012 STATION AVE RM 348 

 FORT HOOD TX 76544-5073 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM CN R SPENCER 

 DCSFDI HF 

 HQ USASOC BLDG E2929 

 FORT BRAGG NC 28310-5000 
NO. OF 

COPIES ORGANIZATION 

29 

 1 ARMY RSCH LABORATORY – HRED 

 RDRL HRM DW E REDDEN 

 BLDG 4 CL 60 

 FORT BENNING GA 31905-5400 

 1 ARMY G1 

 (CD DAPE MR B KNAPP 

 only) 300 ARMY PENTAGON RM 2C489 

 WASHINGTON DC 20310-0300 

 

ABERDEEN PROVING GROUND

 5 DIR USARL 

 RDRL CIM G 

 S FOPPIANO 

 RDRL HR 

 L ALLENDER 

 T LETOWSKI 

 RDRL HRM 

 P SAVAGE-KNEPSHIELD 

 RDRL HRS D 

 B AMREIN 
30

INTENTIONALLY LEFT BLANK.