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The Muscle Morphology of Elite Sprint Running
Article in Medicine and Science in Sports and Exercise · October 2020
DOI: 10.1249/MSS.0000000000002522

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SEE PROFILEThe Muscle Morphology of Elite Sprint Running
ROBERT MILLER1,2, THOMAS G. BALSHAW1, GARRY J. MASSEY3, SUMIAKI MAEO4, MARCEL B. LANZA5,MICHAEL JOHNSTON2,6, SAM J. ALLEN1, and JONATHAN P. FOLLAND1
1

School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire, UNITED KINGDOM; 2British
Athletics, Loughborough University, Leicestershire, UNITED KINGDOM; 3School of Sport and Health Sciences, University of
Exeter, Devon, UNITED KINGDOM; 4Research Organization of Science and Technology, Ritsumeikan University, Kusatsu,
Shiga, JAPAN; 5Department of Physical Therapy and Rehabilitation, University of Maryland Baltimore, Baltimore, MD;
and 6Applied Sports Technology Exercise and Medicine Research Centre, Swansea University, Swansea, UNITED KINGDOMABSTRACTMILLER, R., T. G. BALSHAW, G. J. MASSEY, S. MAEO, M. B. LANZA, M. JOHNSTON, S. J. ALLEN, and J. P. FOLLAND. The Muscle Morphology of Elite Sprint Running. Med. Sci. Sports Exerc., Vol. 53, No. 4, pp. 804–815, 2021. The influence of muscle morphology andstrength characteristics on sprint running performance, especially at elite level, is unclear. Purpose: This study aimed to investigate the differences in muscle volumes and strength between male elite sprinters, sub-elite sprinters, and untrained controls and to assess the relationships
of muscle volumes and strength with sprint performance. Methods: Five elite sprinters (100-m season’s best equivalent [SBE100],
10.10 ± 0.07 s), 26 sub-elite sprinters (SBE100, 10.80 ± 0.30 s), and 11 untrained control participants underwent 1) 3-T magnetic resonanceimaging scans to determine the volume of 23 individual lower limb muscles/compartments and 5 functional muscle groups and 2) isometricstrength assessment of lower body muscle groups. Results: Total lower body muscularity was distinct between the groups (controls < sub-elite+20% < elite +48%). The hip extensors exhibited the largest muscle group differences/relationships (elite, +32% absolute and +15% relative[per kg] volume, vs sub-elite explaining 31%–48% of the variability in SBE100), whereas the plantarflexors showed no differences between
sprint groups. Individual muscle differences showed pronounced anatomical specificity (elite vs sub-elite absolute volume range, +57% to−9%). Three hip muscles were consistently larger in elite vs sub-elite (tensor fasciae latae, sartorius, and gluteus maximus; absolute,+45%–57%; relative volume, +25%–37%), and gluteus maximus volume alone explained 34%–44% of the variance in SBE100. The isometricstrength of several muscle groups was greater in both sprint groups than controls but similar for the sprint groups and not related to SBE100.
Conclusions: These findings demonstrate the pronounced inhomogeneity and anatomically specific muscularity required for fast sprinting
and provides novel, robust evidence that greater hip extensor and gluteus maximus volumes discriminate between elite and sub-elite sprinters
and are strongly associated with sprinting performance. Key Words: SPRINTING, MUSCLE VOLUME, ISOMETRIC STRENGTH

S

strong relationships between muscle volume and neuromuscular power of single muscle groups (2). This suggests that muscle volume may be of critical importance for sprint performance,
and although it is a common observation that elite sprinters are
typically more muscular than untrained populations, the specific muscle groups important for elite sprint running performance remain unclear.
The “gold standard” method of measuring muscle volume ismagnetic resonance imaging (MRI [3]); however, to date, onlya small number of studies have used MRI to investigate the importance of muscle volumes for sprint running performance.
Recent evidence supports the notion that sprinters are generally
more muscular (i.e., greater muscle volume) than nonsprinters(controls), but with a nonuniform pattern of muscular hypertrophy such that the hip and biarticular hip and knee joint muscles appear to be larger, whereas the monoarticular knee joint
muscles and muscles of the lower leg may be more similar(4,5). Moreover, there are also suggestions that the volumeof specific muscles could be related to sprint performance, although with considerable confusion about which muscles/
muscle groups may be most important; for example, there
are reports that psoas major (6–8), rectus femoris (4), adductors (8,9), hamstrings (7,9), quadriceps (8), or even ratios of

APPLIED SCIENCES

print running, including the ability to accelerate quickly
and achieve high maximum running speeds, is one of
the most revered and long-standing expressions of human athletic performance and is considered a key componentof numerous running-based sports. Elite sprinters are capableof achieving impressive gait speeds of over 12 m·s−1 (1) because of the generation of extremely high muscular power,
particularly from the major muscle groups of the lower body.
Theoretically, neuromuscular power is largely determined bymuscle volume, and empirical evidence has demonstrated very

Address for correspondence: Jonathan P. Folland, Ph.D., School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire LE11
3TU, United Kingdom; E-mail: J.P.Folland@lboro.ac.uk.
Submitted for publication May 2020.
Accepted for publication September 2020.
Supplemental digital content is available for this article. Direct URL citations
appear in the printed text and are provided in the HTML and PDF versionsof this article on the journal’s Web site (www.acsm-msse.org).
0195-9131/20/5304-0804/0
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DOI: 10.1249/MSS.0000000000002522

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sub-elite sprinters, and untrained controls and to assess the relationships of both muscle volumes and strength with sprint performance among sprinters. It was hypothesized that the hip
flexor and extensor muscles would be progressively larger relative to body mass according to group (controls < sub-elite < elite)
and be related to sprint performance among the whole cohort ofsprinters. In addition, it was postulated that isometric torque ofthe hip flexor and extensor muscle groups would be different
between groups and related to sprint performance.

muscle volumes (psoas major:quadriceps (10), gluteus maximus:
quadriceps [7]) may be most important. This confusion may havearisen as most studies have examined only a limited and variable
number of muscles or muscle groups (7–11) rather than a complete analysis of the lower body musculature.
Importantly, comparisons to date have also been limited tosprinters versus controls (4,5) or sprinters versus endurance
runners (9) rather than what distinguishes elite from sub-elite
sprinters. This is because previous studies have not included
athletes that are genuinely elite (i.e., internationally competitive), with the fastest personal best 100-m times of participants
being 10.68 s (11), 10.67 s (4), 10.23 s (7), 10.95 s (10), division 1 collegiate level sprinters (performance times undefined[5]), and 13.24 s in preadolescent boys (8). Finally, the numberof sprinters assessed has typically been relatively small for
quantifying the relationship between sprint performance andmuscle volumes (n = 8–16 [4,5,8,9,11]). Thus, no comparison
between elite and sub-elite sprinters has yet been made, andthe muscle groups that need to be particularly large to attainelite running speeds remains to be elucidated.
Similarly, the functional characteristics of specific muscle
groups needed for elite sprint running remain largely unknown. Although some studies have assessed strength, duringmultiple joint exercises (e.g., squatting, isometric mid-thighpull) in relation to acceleration and/or sprint performance of
athletic groups (12,13), this clearly does not allow the identification of which specific muscle groups need to be strong/
powerful to enable fast running. Although it has been speculated that hip flexion and extension strength may be criticalfor fast running (6,7), we are aware of only one preliminary
study that reported these muscle groups to be stronger insprinters and largely predictive of sprint performance (14). In
fact, to date, no studies have done a comprehensive assessment of the strength of a range of ankle, knee, and hip joint
muscles in elite and/or sub-elite sprinters as well as untrained
controls to understand the functional characteristics that may
differentiate these groups.
Therefore, the aims of this study were to investigate the differences in muscle volumes and strength between elite sprinters,

METHODS
Participants and sprint performance. All of the participants were healthy young men, asymptomatic for leg orback injury, with no minor injury in the previous 4 wk andno major injury in the previous 6 months. Five elite sprinters(mean ± SD; age, 27 ± 4 y; body mass, 86.4 ± 6.7 kg; height,
1.83 ± 0.06 m), 26 sub-elite sprinters (22 ± 2 yr, 75.4 ± 7.3 kg,
1.78 ± 0.06 m), and 11 control participants (26 ± 3 yr,
75.2 ± 5.6 kg, 1.80 ± 0.08 m; Table 1) volunteered to participate and gave informed consent to take part in this study. Elitesprinters were required to have a season’s best 100-m sprinttime of <10.25 s (the British Athletics 100 m selection standard for the European Outdoor Championships 2018 [15]).
Sub-elite sprinters were required to have a season’s best timeof 10.35–11.50 s for 100 m or equivalent for 60 m/200 m
based on International Association of Athletics Federations(IAAF) points and to have completed at least one season ofhigh-intensity sprint-specific training. Participants in bothsprint groups completed a minimum of two sprint-specifictraining sessions and one resistance training session per week.
Control participants had a low to moderate level of physicalactivity (i.e., vigorous-intensity activity ≤2 times per week,and ≤1500 MET·min·wk−1, overall vigorous and moderate
physical activity ≤3000 MET·min·wk−1 [16]) and were not involved in systematic physical training or competitive sports (for≥1 yr). Season’s best and personal best sprint (60, 100, and
200 m) times were taken from the national governing body database (www.thepowerof10.info) of electronically timed races withTABLE 1. Performance, training status and anthropometric characteristics of elite sprinters (n = 5), sub-elite sprinters (n = 26), and untrained controls (n = 11).
Controls

Elite Sprinters

Mean ± SD

Range

Mean ± SD

Range

–
–
–
–
2006 ± 825

10.80 ± 0.30
10.69 ± 0.26
5.3 ± 2.6
3.5 ± 2.0

10.36–11.50
10.34–11.25

10.10 ± 0.07**
9.99 ± 0.07**
9.2 ± 3.4**
8.1 ± 2.6**

10.03–10.21
9.91–10.08

25.8 ± 2.6
1.80 ± 0.08
75.2 ± 5.6
23.3 ± 1.8
88 ± 32
15.5 ± 4.3
63.5 ± 4.7
0.81 ± 0.02

22.0 ± 2.2††
1.78 ± 0.06
75.4 ± 7.3
24.3 ± 2.4
53 ± 14††11.2 ± 3.1††
67.0 ± 6.7
0.82 ± 0.04

27.4 ± 4.1**
1.83 ± 0.06
86.4 ± 6.7**†
25.0 ± 1.0
39 ± 4††8.3 ± 1.2††
79.8 ± 6.1**††0.84 ± 0.05

Data are presented as mean ± SD.
Significantly different to sub-elite: *P ≤ 0.05 and **P ≤ 0.01.
Significantly different to controls: †P ≤ 0.05 and ††P ≤ 0.01.

MUSCLE MORPHOLOGY OF SPRINT RUNNING

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805

APPLIED SCIENCES

Performance and training status
SBE100 (s)PBE100 (s)Sprint training duration (yr)Resistance training duration (yr)Activity level (MET·min·wk−1)
Anthropometrics
Age (yr)
Height (m)Body mass (kg)Body mass index (kg·m−2)
Sum of eight skinfold (mm)Body fat percentage (%)
Fat-free mass (kg)
Waist–glute ratio (−)

Sub-elite Sprinters

Mean ± SD

APPLIED SCIENCES

wind readings (<2.0 m·s−1) during the corresponding calendar
year in which data collection took place (season’s best) or
the athletes career at the end of that season (personal best).
Sprint performances were converted to IAAF points, a classification system that allows performance comparisons between
different events, and each athletes maximum points in any of
the sprint events (60, 100, and 200 m) was taken as their performance measure and converted back into 100-m season’s bestequivalent (SBE100) or personal best equivalent (PBE100) times.
For the elite sprint group, SBE100 (10.10 ± 0.07; range,
10.03–10.21 s) and PBE100 (9.99 ± 0.07; range, 9.91–10.08 s)
were actual 100-m performances for all individuals (i.e.,
100-m was their best event). For the sub-elite sprint group,
SBE100 was actual 100-m performances for 73% of these athletes (19 out of 26), whereas for seven athletes, SBE100 was
derived from either 60- or 200-m season’s best times. Consequently, the whole sprint cohort had SBE100 ranging from10.03 to 11.50 s (10.71 ± 0.37 s). Ethical approval was grantedby the Loughborough University Ethics Approvals (Human
Participants) Sub-Committee.
Study overview. Participants were required to attend two
measurement sessions within this cross-sectional study: onefor isometric strength measurements and one for assessing
muscle morphology (MRI). All measurement sessions werescheduled after a rest day or light training day, and participants
were instructed to arrive in a relaxed state having followed
normal daily activity and dietary behaviors, where they thensat quietly for 15 min before their MRI scan. Because of limitations in scheduling and practicalities of data collection withelite athletes, it was not feasible to control for measurement
time of day.
Anthropometry. Body mass was measured using a calibrated ADAM C-150 weighing scale (ADAM equipment,
Oxford, CT), and stature was measured using a wall-mounted
stadiometer (Holtain Ltd., Crymmych, UK). Skinfold thickness
was measured at eight sites (bicep, tricep, subscapular, iliac crest,
supraspinale, abdominal, thigh, and calf ) using Harpenden
skinfold calipers (British Indicators Ltd., Wolverhampton, UK),and the averages of two measurements at each site were recorded. In addition, waist and gluteal circumferences werecollected. All anthropometric measures were done by the sameinvestigator and in accordance with the International Society
for the Advancement of Kinanthropometry guidelines (17).
The sum of four skinfolds (bicep, tricep, subscapular, and iliac
crest) was used to calculate body density using the formula formales 20–29 yr old (18), and percentage body fat was estimated using the Siri (19) equation. Fat-free mass was derived
from the percentage body fat and body mass values.
Muscle volume with MRI. T1-weighted axial magnetic
resonance (MR) images of the abdomen, thigh, and shankwere obtained with a 3-T scanner (Discovery MR750w; GE
Healthcare, Chicago, IL) with a receiver 8-channel wholebody coil. Images (time of repetition, 600 ms; time of echo,
8 ms; field of view, 450  450 mm; image matrix,
320  320; pixel size, 1.4  1.4 mm; slice thickness, 5 mm;interslice gap, 5 mm) were obtained from the 12th thoracic

806

Official Journal of the American College of Sports Medicine

vertebra to the calcaneus capturing both legs in five overlapping
blocks. Subjects were scanned while in the supine position witharms folded across the chest, with hip and knee joints extended
and the ankle joint at ~90°. Oil-filled capsules were placed inequal segments on the right leg of each participant during scanning to facilitate alignment between the blocks during analysis.
The MR images were manually segmented to assesscross-sectional area and to derive the volume of 23 lower limb
muscles/compartments. Specifically, every other MR image(i.e., 20 mm between the center of the measured images)
starting from the most proximal image in which the muscle appeared was segmented using a public domain DICOM software(Horos, version 2.2.0 www.thehorosproject.org). The average
number of images analyzed per muscle is shown in Table 2.
Six separate investigators conducted the analysis, with each
investigator analyzing the same muscles/compartments forthe entire cohort, and blinded to participant identity/group.
Fully analyzed images for each participant (i.e., all 26 muscles/
compartments) were then checked and quality assured for accuracy by a single investigator (RM), paying particular attention to errors and overlaps between adjacent muscle crosssections. The analyzed muscles/compartments were iliopsoas(psoas major and iliacus combined); sartorius; tensor fasciae
latae (TFL); adductor magnus; gracilis; gluteus maximus; gluteus medius; gluteus minimus; rectus femoris; vastus lateralis,
medialis, and intermedius; semimembranosus; semitendinosus;
biceps femoris long and short heads; popliteus; lateral and medial gastrocnemius; soleus; and the anterior, lateral, and deep
posterior compartments of the shank. The shank compartments
were the combined volume of the following muscles: tibialis
anterior, extensor digitorum longus, and extensor hallux longus(anterior); peroneus longus and brevis (lateral); and plantaris,
tibialis posterior, flexor digitorum longus, and flexor hallux
longus (deep posterior). The volume of five functional muscle
groups was calculated as the sum of the following muscles:
hip extensors (gluteus maximus, adductor magnus, biceps
femoris long head, semimembranosus, and semitendinosus),
hip flexors (iliopsoas, rectus femoris, sartorius, and TFL), knee
extensors (rectus femoris, vastus intermedius, medialis, andlateralis), knee flexors (gracilis, biceps femoris long and shorthead, semimembranosus, semitendinosus, sartorius, popliteus,
and medial and lateral gastrocnemius), and plantarflexors (medial and lateral gastrocnemius and soleus).
The volume of each muscle (Vm) was calculated using previously outlined methods (7):
Vm ¼

n−1
X
h
i¼1

2

ðAmi þ Amiþ1 Þ

where Am represents the muscle cross-sectional area calculated
from each image, i is the image number, n is the total numberof images, and h is the distance between images (20 mm). In
addition to absolute muscle volume (cm3), muscle volume
was also expressed relative to body mass (cm3·kg−1).
Strength measurements. The isometric strength of thefive functional muscle groups was assessed with custom-built
isometric dynamometers in the following order (for reference

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TABLE 2. Absolute and relative muscle volume of all muscles, five functional muscle groups, and 23 individual muscles/compartments of elite sprinters (n = 5), sub-elite sprinters (n = 26), anduntrained controls (n = 11).
Muscle Group/Muscle
or Compartment
All muscles
Hip flexors
Hip extensors
Knee flexors
Knee extensors
Plantarflexors
Iliopsoas
Sartorius
TFL
Adductor Magnus
Gracilis
Gluteus maximus
Gluteus medius
Gluteus minimus
Rectus femoris
Vastus lateralis
Vastus intermedius
Vastus medialis
Semimembranosus
Semitendinosus
Biceps femoris long head
Biceps femoris short head
Popliteus
Lateral gastrocnemiusMedial gastrocnemius
SoleusAnterior compartment
Lateral compartment
Posterior compartment

Absolute Muscle Volume (cm3)

Relative Muscle Volume (cm3·kg−1)

No. Slices

Control Group

Sub-elite Sprinters

Elite Sprinters

Control Group

Sub-elite Sprinters

Elite Sprinters

18
28
15
16
17
16
10
9
21
22
23
19
17
15
18
7
16
13
14
22
20
21
20

7628 ± 1548
1031 ± 151
2257 ± 220
1460 ± 196
2202 ± 315
860 ± 172514 ± 75
142 ± 2573 ± 24624 ± 8198 ± 23931 ± 108384 ± 49
199 ± 39303 ± 55743 ± 98680 ± 115476 ± 111262 ± 18219 ± 39
221 ± 42110 ± 28
19 ± 6156 ± 41251 ± 52453 ± 95291 ± 47
153 ± 35326 ± 939164 ± 1207††
1314 ± 216††
3029 ± 422††
1859 ± 301††
2636 ± 401††
943 ± 156618 ± 101†
209 ± 50††86 ± 25828 ± 128††142 ± 37††1257 ± 197††
405 ± 69
170 ± 36401 ± 78††925 ± 156††789 ± 140521 ± 79327 ± 59††
350 ± 79††267 ± 47†131 ± 34
17 ± 5170 ± 37262 ± 58
510 ± 76273 ± 47
161 ± 42345 ± 7111323 ± 1328**††1620 ± 200**††4002 ± 489**††2304 ± 178**††3218 ± 400**††1112 ± 181†702 ± 97††306 ± 46**††135 ± 41**††1056 ± 83**††180 ± 37††
1797 ± 376**††434 ± 92
192 ± 46476 ± 45††1132 ± 180†962 ± 145*††649 ± 97*††359 ± 60††449 ± 70*††340 ± 31**††167 ± 26††
23 ± 5202 ± 34
300 ± 38
610 ± 137††
302 ± 59
147 ± 32401 ± 76

101.42 ± 7.55
13.75 ± 2.16
30.10 ± 3.14
19.45 ± 2.72
29.21 ± 3.09
11.39 ± 1.92
6.84 ± 1.03
1.89 ± 0.28
0.97 ± 0.36
8.30 ± 0.88
1.31 ± 0.30
12.40 ± 1.39
5.11 ± 0.51
2.66 ± 0.58
4.05 ± 0.81
9.88 ± 1.20
9.01 ± 1.20
6.28 ± 1.11
3.50 ± 0.33
2.93 ± 0.64
2.97 ± 0.71
1.46 ± 0.36
0.26 ± 0.06
2.06 ± 0.47
3.33 ± 0.62
6.00 ± 1.08
3.87 ± 0.53
2.02 ± 0.39
4.32 ± 1.12

121.51 ± 10.05††
17.42 ± 2.27††
40.16 ± 3.77††
24.61 ± 2.79††
35.00 ± 4.36††
12.48 ± 1.40
8.18 ± 0.97††
2.77 ± 0.62††
1.14 ± 0.29
10.99 ± 1.46††
1.89 ± 0.45††
16.65 ± 1.82††
5.38 ± 0.75
2.25 ± 0.44
5.33 ± 0.98††
12.26 ± 1.65††
10.48 ± 1.63†
6.92 ± 0.89
4.34 ± 0.63††
4.63 ± 0.86††
3.55 ± 0.54†
1.73 ± 0.39
0.22 ± 0.07
2.25 ± 0.38
3.50 ± 0.42
6.77 ± 0.76
3.62 ± 0.52
2.13 ± 0.46
4.57 ± 0.82

131.26 ± 6.76††
18.82 ± 1.83††
46.39 ± 2.88**††26.78 ± 0.76††
37.31 ± 2.48††
12.92 ± 1.78
8.18 ± 1.10
3.56 ± 0.40*††
1.56 ± 0.39*††
12.31 ± 1.05††
2.10 ± 0.39††
20.75 ± 3.15**††5.01 ± 0.75
2.22 ± 0.48
5.53 ± 0.38†
13.07 ± 1.09††
11.17 ± 1.33†
7.53 ± 0.89
4.16 ± 0.56
5.20 ± 0.54††
3.96 ± 0.32††
1.94 ± 0.29
0.27 ± 0.05
2.36 ± 0.51
3.50 ± 0.42
7.05 ± 1.25
3.48 ± 0.46
1.69 ± 0.27
4.63 ± 0.60

The number of axial images/slices used to assess the volume of each muscle were averaged across all participants. Muscle volume data are presented as group mean ± SD, with individual
measurements the average of both sides/legs (i.e., unilateral). All Muscles is the sum of muscle volumes from all the individual muscles/compartments listed.
Significantly different to sub-elite: *P ≤ 0.05 and **P ≤ 0.01.
Significantly different to controls: †P ≤ 0.05 and ††P ≤ 0.01.

MUSCLE MORPHOLOGY OF SPRINT RUNNING

third contraction was completed if the participant scored higher
on their second contraction than the first. During the maximal
contractions, participants were given strong verbal encouragement, instructed to push as hard as possible for the duration of thecontraction, and provided with real-time biofeedback displayedon a computer monitor with a target cursor representing theirmaximum force in preceding contractions. Maximal voluntary
force was the highest instantaneous force achieved, corrected
for the force due to gravity (i.e., baseline force at rest), andmaximal voluntary torque was calculated as the product of
maximal voluntary force and measured lever length (m). For
the hip and the knee muscle groups, lever length was manually
measured as the distance between the center of the strap andthe center of rotation of the respective joint. To calculate
plantarflexion lever length, sagittal plane video was recorded
synchronous to the force measurement at 60 Hz during the
maximal voluntary contractions with a camera (Panasonic
HC-V110; Panasonic, Kadoma, Japan) placed 4 m perpendicular to the movement plane, with the field of view maximized
with optical zoom and markers on the knee joint, lateralmalleolus, and lateral head of the fifth metatarsal. The cornersof the force plate and ankle location were manually digitized,
and ankle torque was calculated as the perpendicular distancefrom the normal force vector to the ankle joint center, multiplied by the magnitude of the normal force vector.
Statistical analysis. Muscle volume and strength measurements assessed on both legs were averaged to provide
unilateral criterion values for each participant. Data are

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807

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hip [180°], knee [180°], and ankle [90°] angles in the anatomical position; flexion is lower): hip extensors (upper bodyprone, hip 145°, knee 150°); hip flexors (upper body supine,
hip 180°, knee 150°); knee extensors (sitting, hip 115°, knee120°); knee flexors (upper body prone, hip 150°, knee 150°);and plantarflexors (sitting, hip 110°, knee 180°, ankle 100°).
Measurements were made unilaterally, first with the right leg
then the left, before moving to the next dynamometer. Participants were tightly secured to each dynamometer using extensive strapping to minimize extraneous movement. Duringextension and flexion of the hip and knee, a calibrated
S-shaped strain gauge (linear response up to 2000 N) and specific braces were positioned in the movement plane perpendicular to the long axis of femoral/tibial movement and strapped
4 cm proximal to the knee/ankle joints, respectively. During
plantarflexion contractions, force data were collected using a
portable Kistler force plate (Type 9602A; Kistler Instruments
Corp., Winterthur, Switzerland) mounted to a custom-built rig.
For all isometric measurements, the force signal was amplified(500), interfaced with an analog-to-digital converter (CED
micro 1401; CED, Cambridge, UK), and sampled at 2000 Hz
with a personal computer using Spike 2 software (CED).
With each dynamometer and muscle group, participants
first completed a standardized series of warm-up contractions,each of 3-s duration with 15-s rest in between (3  50%,
3  75%, 1  90% perceived maximum) followed by at least
two subsequent maximal voluntary contractions of the relevantmuscle group, lasting ~4 s with at least 60-s rest in between. A

muscle). All statistical procedures were performed with IBM
SPSS Statistics Version (IBM Corp., New York, NY).

RESULTS
Anthropometrics. Elite sprinters were similar in stature
but heavier (>10 kg) than both sub-elite sprinters and untrained
controls (P = 0.006 and P = 0.013 respectively; Table 1). Bothsprint groups had a lower percentage body fat and sum of eightskinfolds compared with controls (P ≤ 0.01). Fat-free mass was
greater in elite sprinters than both sub-elite sprinters (>12 kg,P ≤ 0.01) and controls (>16 kg, P ≤ 0.01).
Comparison of absolute muscle volumes. The total
unilateral volume of all the measured muscles was greaterfor both sprint groups vs controls (elite, +48%; sub-elite,+20%; both P < 0.01) and for the elite versus sub-elite
sprinters (+24%; P = 0.01; Table 2). Elite sprinters had greater
absolute muscle volume than sub-elite sprinters for four functional muscle groups (hip extensors, +32%; knee flexors,+24%; hip flexors, +23%; knee extensors, +22%; all P ≤ 0.01;
Fig. 1), but not the plantarflexors. Compared with controls,
sub-elite sprinters had greater muscle volume of four functional
muscle groups (+20%–34%, P ≤ 0.009, except the plantarflexors;
see Figure, Supplemental Digital Content 1, Percentage differences in absolute and relative muscle volumes between sub-elite
sprinters vs controls, http://links.lww.com/MSS/C150). The
functional muscle groups and individual muscles are ordered according to the magnitude of the percentage differences for absolute muscle volume), and elite sprinters wereAPPLIED SCIENCES

presented as mean ± SD. The Shapiro–Wilk test was used toassess the normality of distribution and revealed that >90%of the variables were normally distributed, in which case weused parametric statistical tests to provide a consistent approach.
One-way ANOVA and subsequent Bonferroni post hoc analysis were used to assess differences between groups for muscle volume (absolute, and relative to body mass), torque(absolute, and relative to body mass), and anthropometry. Statistical significance was set at P < 0.05. For the whole cohortof sprinters (i.e., elite and sub-elite groups combined, not including the control group), the bivariate relationships between
SBE100 and measures of muscle volume and strength wereassessed using Pearson’s product moment correlation. Correlation coefficients were categorized as “weak” (r ≤ 0.40), “moderate” (r = 0.40–0.60), “strong” (r = 0.60–0.80), or “very strong”(r = 0.8–1.0). Correlation P values were corrected for multiple
tests using the Benjamini–Hochberg (20) method with a false discovery rate of 5%, and the significance level was defined as adjusted P < 0.05. Stepwise multiple linear regression was used
to calculate the variance in SBE100 explained by the best combination of variables in each of the following categories: absoluteand relative muscle volume of individual muscles and muscle
groups. In practice, based on their significant bivariate correlations with SBE100, the following were entered into four distinct
regression analyses for each of these categories of variables:(i) absolute volume of muscle groups (5 muscle groups), (ii)absolute muscle volume of individual muscles (18 specific muscles), (iii) relative volume of muscle groups (2 muscle groups),and (iv) relative volume of individual muscles (1 specific

FIGURE 1—Percentage differences in absolute and relative muscle volumes of all muscles, five functional muscle groups, and 23 individual muscles/compartments between elite (n = 5) and sub-elite (n = 26) sprinters. A positive value indicates greater volume of elite sprinters. The functional muscle groups andindividual muscles are ordered according to the magnitude of the percentage differences for absolute muscle volume.

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MUSCLE MORPHOLOGY OF SPRINT RUNNING

TABLE 3. Pearson’s product moment correlation coefficients between SBE100 and absoluteand relative muscle volume of all muscles, five functional muscle groups, and 23 individual
muscles in the whole cohort of sprinters (n = 31).
Muscle Group/Muscle
All muscles
Hip flexors
Hip extensors
Knee flexors
Knee extensors
Plantarflexors
Iliopsoas
Sartorius
TFL
Adductor magnus
Gracilis
Gluteus maximus
Gluteus medius
Gluteus minimus
Rectus femoris
Vastus lateralis
Vastus intermedius
Vastus medialis
Semimembranosus
Semitendinosus
Biceps femoris long head
Biceps femoris short head
Popliteus
Lateral gastrocnemiusMedial gastrocnemius
SoleusAnterior compartment
Lateral compartment
Posterior compartment

Absolute Muscle
Volume (cm3)

Relative Muscle
Volume (cm3·kg−1)−0.629**−0.563**−0.689***−0.682***−0.495**−0.537**−0.442*−0.639***−0.547**−0.582**−0.564**−0.662***−0.227−0.254−0.409*−0.475*−0.443*−0.431*−0.478*−0.530**−0.475*−0.511*−0.435*−0.578**−0.437*−0.474*−0.272−0.192−0.290−0.422*−0.299−0.560**−0.522**−0.178−0.309−0.120−0.484−0.454−0.289−0.377−0.580*0.152
0.040−0.090−0.199−0.154−0.114−0.194−0.342−0.190−0.341−0.260−0.398−0.230−0.196
0.092
0.045
0.014

Significant correlations: *P ≤ 0.05, **P ≤ 0.01, and ***P ≤ 0.001, following correction for
multiple comparisons.

(r = −0.689, P < 0.001) and the gluteus maximus from amongst
the individual muscles (r = −0.639, P < 0.001; Fig. 2). Relative tobody mass, the combined volumes of all the muscles(r = −0.422, P = 0.036), two muscle groups (hip extensors
r = −0.560, P = 0.005, and knee flexors r = −0.522,
P = 0.006), and only one individual muscle (gluteus maximus
r = −0.580, P = 0.014) were moderately associated with
SBE100 (Fig. 2). Two further individual muscle volumes relative to body mass, however, displayed a tendency to be moderately related to SBE100 (sartorius r = −0.484, P = 0.066; TFL
r = −0.454, P = 0.079). The regression models revealed that
only the single strongest predictor variable contributed to the
explained variance in SBE100 within each category of predictor
variables: absolute volume of muscle groups, hip extensors explained 47.5% of the variance in SBE100; relative volume ofmuscle groups, hip extensors explained 31.4% of the variance;
absolute volume of individual muscles, gluteus maximus explained 43.8% of the variance; and relative volume of individual muscles, gluteus maximus explained 33.6% of the variance.
Isometric strength. Sub-elite sprinters had greater absolute strength of the knee extensors (+26%, P = 0.001) andflexors (47%, P = 0.005) compared with controls, but withno differences in any other muscle groups. Elite sprinters
showed a distinct pattern of differences compared with controls
with greater absolute strength of the hip flexors (+55%,
P = 0.002) and extensors (+63%, P = 0.002) and knee flexors(+62%, P = 0.013; Fig. 3). When relative torque was compared,
sub-elite sprinters outperformed controls across all muscle

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larger in all five functional muscle groups (+29%–77%, allP ≤ 0.020). When comparing the absolute volume of individual muscles/compartments between groups, there werenonuniform differences and pronounced anatomical specificity, e.g., elite vs sub-elite sprinters ranging from +57%
(TFL) to −9% (lateral compartment of the shank). Eight individual muscles were larger in elite vs sub-elite sprinters(all P ≤ 0.035): TFL (+57%), sartorius (+47%), gluteus
maximus (+45%), adductor magnus (+28%), semitendinosis(+28%), biceps femoris long head (+27%), vastus medialis(+24%), and vastus intermedius (+22%). Furthermore, compared with controls, elite sprinters had 15 out of 23 muscles/
compartments that were larger (+36%–106%, P ≤ 0.018),
and sub-elite sprinters had 10 muscles/compartments thatwere larger (+19%–60%, P ≤ 0.019). In summary, for absolute muscle volumes, similar differences were noted for thetwo comparisons between sub-elite sprinters vs controls
and elite vs sub-elite sprinters (see Table, Supplemental
Digital Content 2, A summary table of the observed significant differences between sub-elite sprinters vs controls,and elite sprinters vs sub-elite sprinters, http://links.lww.
com/MSS/C151).
Comparison of relative muscle volumes. Regarding
relative muscle volume, the total volume of the measured muscles was greater in sprint groups vs controls (elite, +29%,
P < 0.001; sub-elite, +20%, P = 0.001), but with no differences
between the sprint groups (P = 0.107). The hip extensors were
the only muscle group to differentiate elite from sub-elite
sprinters based on relative muscle volume (+15%, P = 0.003),
and the only individual muscles that had larger relative muscle
volume in the elite vs sub-elite sprinters were the gluteus
maximus (+25, P ≤ 0.001), sartorius (+28%, P = 0.013), andTFL (+37%, P = 0.032). Compared with controls, both sprintgroups had greater relative muscle volume of the flexors andextensors of the hip and knee (i.e., four muscle groups;+20%–54%; all P ≤ 0.001), but there were no differences forthe plantarflexors. In addition, in comparison with controls,
the sprint groups had 13 (elite sprinters, +24%–77%) and 12(sub-elite sprinters, +16%–58%) larger individual muscles relative to body mass. In summary, for relative muscle volumes, although there were many differences between sub-elite sprintersand controls, there were far fewer differences between elite andsub-elite sprinters (see Table, Supplemental Digital Content 2,
A summary table of the observed significant differences between
sub-elite sprinters vs controls, and elite sprinters vs sub-elite
sprinters, http://links.lww.com/MSS/C151).
Relationships between sprint performance andmuscle volumes. Among the whole sprint cohort, SBE100
showed moderate to strong correlations with absolute muscle
volume of all the muscles combined (r = −0.629, P < 0.001), eachof the five muscle groups (r = −0.495 to −0.689, P ≤ 0.05;
Table 3), as well as 18 out of 23 individual muscles/
compartments (r = −0.409 to −0.662; all P ≤ 0.05), i.e., only
five individual muscles were not correlated with SBE100.
The highest correlations of absolute muscle volumes with
SBE100 were the hip extensors from among the muscle groups

FIGURE 2—The relationships between SBE100 and absolute hip extensor volume (A); relative hip extensor volume (B); absolute gluteus maximus volume (C);and relative gluteus maximus volume (D). Significant correlations: *P ≤ 0.05; **P ≤ 0.01; and ***P ≤ 0.001 following correction for multiple comparisons.

groups (mean difference + 34%, P ≤ 0.027). Similar to absolute
torque, the elite group produced greater relative torque than thecontrols during hip extension (+48%, P = 0.002), hip flexion(+40%, P = 0.007), and knee flexion (+49%, P = 0.049) thanthe controls. However, there were no differences observed inabsolute or relative torque between elite and sub-elite sprinters
across any of the five muscle groups (Fig. 3).
Absolute strength of all five muscle groups was unrelated tosprint performance. For relative strength, counterintuitively
one muscle group, relative knee extensor strength, was positively correlated with SBE100 (r = 0.485, P = 0.033; i.e.,
greater knee extension torque, slower sprint time), but there
were no relationships for other muscle groups (r = −0.265 to
0.139, P > 0.105).

APPLIED SCIENCESDISCUSSION
The aims of this study were to compare the lower bodymuscle volumes and strength characteristics between a groupof genuinely elite sprinters with sub-elite sprinters and untrained controls and to assess the relationships of these measures with sprint performance among sprinters. MRI analysis
revealed that total lower body muscularity was distinct between all three groups (vs controls: sub-elite, +20%; elite,+48%), such that the elite sprinters had ~3.7 kg and ~2.2 kgof extra muscle mass per leg than controls and sub-elite
sprinters, respectively. However, the differences in muscle volume between the groups were highly nonuniform with substantial anatomical specificity according to muscle group andespecially individual muscle. For elite vs sub-elite sprinters,
the largest muscle group–specific effects were found primarily
for the hip extensors (differences of +32% absolute and+15% relative volume, explaining 47.5% [absolute volume]

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to 31.4% [relative volume] of the variability in performance)and secondarily for the knee flexors (differences of +24% absolute volume; performance correlations for absolute [r = −0.682]
and relative [r = −0.522] volume), whereas the plantarflexors
showed no differences between the sprint groups. Individual
muscles showed even greater anatomical specificity with threemuscles being larger in elite vs sub-elite sprinters in both absolute and relative terms (TFL: absolute, +57%; relative, +37%;
sartorius: absolute, +47%; relative, +28%; gluteus maximus: absolute, +45%; relative, +25%), and the gluteus maximus alone
explained 33.6% (relative volume) to 43.8% (absolute volume)of the variance in performance among sprinters. Although bothsprint groups had stronger hip and knee muscle groups thancontrols, isometric strength did not differentiate between sprintgroups and was unrelated to sprint performance. Therefore, thisstudy provides novel and robust evidence highlighting the importance of specific morphological characteristics, principally hip
extensor and gluteus maximus volume, for elite sprint running.
For the control group in this study, both muscle volume andknee joint muscular strength were comparable with previously
published investigations using similar measurements in analogous populations (21–23). Both sprint groups demonstrated
relatively large muscle volumes when compared with previous
studies; however, comparison with previous literature is confounded by differences in performance standard, the inclusionof both male and female sprinters in some studies (5), and potential ethnic differences (7). The performance standards of theelite sprinters in this study (n = 5; SBE100, 10.03–10.21 s;
PBE100, 9.91–10.08 s) were all faster than any previously
studied individual sprinter or cohort (e.g., fastest personal best
10.23–11.71 s [4,7,9]). The sub-elite group in the current study(PBE100, 10.34–11.24 s) was of a comparable, if not higher,
performance standard to previous research. Hence, this

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FIGURE 3—Comparison of absolute and relative isometric maximum voluntary torque of five functional muscle groups between elite (n = 5) vs sub-elite(n = 26) sprinters vs untrained controls (n = 11). Data are presented as group mean ± SD, with individual measurements the average of both legs. Significantly different to controls: *P ≤ 0.05 and **P ≤ 0.01.

MUSCLE MORPHOLOGY OF SPRINT RUNNING

particularly individual muscles/compartments. Specificallythere were differences between all three groups (elite>subelite>controls) for four out of five muscle groups, with thegreatest differences in hip extensors (sub-elite, +34%; elite,+77% vs controls) followed by the knee flexors (+27%;+58%), hip flexors (+27%; +57%), and knee extensors(+20%; +46%), but only the elite sprinters > controls forthe plantarflexors (+29%). The broad pattern of these findings, with the largest differences in the hip and knee joint
muscles but less pronounced differences for the ankle joint
muscles, is in accordance with previous research comparing
sub-elite sprinters with nonsprinters (4,5). The current study
has extended those findings, with elite runners found to haveparticularly pronounced muscularity of the hip extensors andflexors, and knee flexors, and thus to our knowledge, this is
the only research study to date highlighting the morphologicalcharacteristics important for elite-level sprinting. At runningspeeds >7.5 m·s−1, there appears to be a disproportionate requirement for power generation by the hip flexors, hip extensors, and knee flexor muscle groups (24). Biomechanically,
the hip extensors are primarily responsible for the back swingof the legs during stance (25), and both the hip extensor and the

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appears to be the first comprehensive comparison of muscle
morphology and strength between genuinely elite sprinterswith sub-elite sprinters and controls.
Absolute muscle volume. Preliminary anthropometrics
revealed that the three groups had similar stature and BMI.
However, both sprint groups were leaner than controls, andthe elite group was heavier (>11 kg) and had greater fat-freemass (>12 kg) than both the other groups. From the MRI analysis, the total muscle volume of all the muscles was distinct
and progressively larger according to sprint performance (controls < sub-elite +20% < elite +48%) with elite sprinters having ~4.4 kg (vs sub-elite) and ~7.4 kg (vs controls) of extra
muscle mass across both legs. These differences in lower limb
muscularity are in accordance with, but more pronounced than,previous studies of sub-elite sprinters (5,7). The mechanistic reasons for the greater muscularity of elite > sub-elite > controls in
the current study are not possible to discern from this investigation, although it seems likely that the sprint and resistance training history of the groups, which shows a similar pattern, would
contribute to these differences in muscularity.
Furthermore, there was extensive anatomical variability inthe magnitude of differences between muscle groups andAPPLIED SCIENCES

knee flexors facilitate the application of horizontal forces to theground (26), and thus these muscle groups are considered critical for propulsion (27). However, the hip flexors are thought
crucial to the rapid acceleration of the legs during swing phaseto achieve high stride frequencies (24,28). From this perspective, it is logical that elite sprinters would be larger in thesemuscle groups.
Individual muscle differences between the groups showedpronounced anatomical specificity with the muscles of elite
vs sub-elite sprinters ranging from +57% (TFL) to −9% (lateral compartment of the shank). Elite sprinters had 8 out of
23 larger muscles/compartments versus sub-elite (+22%–
57%: TFL, sartorius, gluteus maximus, semitendinosus, adductor magnus, biceps femoris long head, vastus intermedius,
and vastus medialis), with 6 of these being hip muscles. Furthermore, both sprint groups had 10 (sub-elite, +20%–47%)
and 15 (elite, +35%–115%) larger muscles/compartments thancontrols. Strikingly, among the sprinters total muscle volume,the volume of all five muscle groups and 18/23 individual
muscles were all found to be related to SBE100 (i.e., greater
volume, faster sprint time). However, strong relationships(r > 0.60), and in fact the highest correlations in this study,
were observed between SBE100 and volume of the hip extensor (r = −0.689) and knee flexor muscle groups (r = −0.682)
as well as two constituent muscles from within these groups(gluteus maximus r = −0.662; and sartorius r = −0.639). The
largest previous study of muscle morphology in sub-elite
sprinters also reported the absolute volume of 4/12 individual
muscles, including the gluteus maximus and hamstrings, to berelated to 100 m time (r = 0.37–0.42 [7]). Inclusion ofelite-level sprinters in the current investigation and the somewhat higher average performance standard of our cohort(10.71 vs 10.94 s [7]) might explain the more pronounced relationships we have found. Subsequently, regression analyses
revealed that the absolute volume of the hip extensors explained 47.5% and gluteus maximus 43.8% of the variancein sprint running performance, respectively. Given the multifactorial nature of sprint running performance, widely considered to depend on an array of anatomical, biomechanical,
physiological, technical, and psychological variables (29),the apparent importance of these specific muscle morphology
characteristics in explaining >40% of the variance in performance is remarkable.
Overall, these findings highlight the importance of the absolute size of specific muscle groups (primarily the hip extensors
and secondarily knee flexors) and muscles (gluteus maximus
and sartorius) for sprint performance. The consistency of ourfindings/differences between sub-elite sprinters versus controls and elite sprinters versus sub-elite sprinters for absolute
muscle volumes (see Table, Supplemental Digital Content 2,
A summary table of the observed significant differences between sub-elite sprinters vs controls, and elite sprinters vs
sub-elite sprinters, http://links.lww.com/MSS/C151), and themost distinct muscle groups/muscles explaining substantial proportions of the variance in sprint performance, reinforces the apparent veracity of these findings. The primary importance of the812

Official Journal of the American College of Sports Medicine

hip extensors (the largest muscle group differences for both elite
vs sub-elite, +32%, and sub-elite vs controls, +34%, explaining
47.5% of the variance in SBE100) and gluteus maximus (greaterfor both elite vs sub-elite, +45%, and sub-elite vs controls,+35%, explaining 43.8% of the variance in SBE100) are original
findings. Previous literature has reported contradictory findings
for the primary importance of various muscle groups and muscles (4,6,8–10), without highlighting the importance of the hip
extensors and gluteus maximus. These investigations typicallyused smaller numbers (n = 8–16) of sub-elite sprinters (fastest
individual 100-m personal best = 10.33 s) and have performed
less comprehensive morphological analyses (i.e., a limited
number of lower body muscles). As discussed above, given
the key role of the hip extensors and gluteus maximus in propulsion (25,26), it is surprising that until now there has been
little empirical evidence to support their importance for sprint
running performance.
The importance of absolute muscularity would certainly be
expected to be beneficial for absolute power production given
the strong association of these variables (R2 ~0.80 [2]), but it
may be surprising given that sprint running has often been
considered to depend on power per unit body mass (i.e., relative muscle volume [30]). However, theoretical analysis has
shown that among runners of similar stature, having greater
absolute muscle mass is biologically necessary to attain fastersprinting speeds (31). The current experiment adds to the data
indicating that absolute muscularity, particularly of key muscle groups and individual muscles, is highly important for
sprint running performance. Although it seems unlikely, an alternative possibility is that the elite sprinters in this study werecoincidentally larger, and therefore the apparent abundance ofdifferences between groups and associations with sprint performance we have observed for absolute muscle volumes
could be an artifact of their coincidentally greater body mass.
In this case, relative muscle volume (per kilogram) facilitates
body mass–independent comparisons, without this potential
confounding difference in body mass between the groups.
Relative muscle volume. Relative muscle volume wasgreater for both sprint groups compared with controls for the
flexors and extensors of the hip and knee. For individual muscles, the differences in relative muscle volume also showedmarked anatomical variability/specificity between the threegroups (e.g., elite vs sub-elite; range, +37% TFL to −21% lateral compartment of the shank). Interestingly, however, only
one muscle group (hip extensors, +15%) and three individual
muscles (gluteus maximus, +25%; sartorius, +28%; and TFL,
+37%) were larger in the elite vs sub-elite sprinters. The TFL
and the sartorius have been highlighted as having large differences in volume between sprinters and controls (5), but this is
the first study where these muscles have been found to be relatively larger in elite vs sub-elite sprinters. Although thesemuscles have received very little attention to date with regard
to their influence on sprint performance, both the TFL and thesartorius are key contributors to hip flexion (32). In addition,
the sartorius is the only simultaneous knee and hip flexor(33), an important combination of actions in changing limb

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MUSCLE MORPHOLOGY OF SPRINT RUNNING

the likelihood of finding more subtle differences between
groups, especially given the small sample size of the elite sprintgroup (n = 5).
No strength measures were found to be related to fastersprint performance, although a counterintuitive finding was
the positive relationship between relative knee extensor strengthand SBE100 (r = 0.485; i.e., the greater the torque, the slower thesprint time). Previous contrary reports include a negative correlation (37) or no relationship (38) between knee extensor
strength and sprint performance in team sports players, rather
than the elite-level and the sub-elite sprinters of the current
study. In addition, work by Dorn and colleagues (24) found thatthe force requirement of the vastii plateaus as running velocity
increases past 5 m·s−1, perhaps suggesting that knee extensor
torque is not a particular limitation of fast running.
Limitations. There are some limitations associated with thepresent investigation. First, for some of the sub-elite sprinters(7/26), SBE100 was an estimation based on their superior IAAF
points at either 60 or 200 m and as such may have overestimatedtheir 100-m performance. However, the difference in group sprint
performance time as a result of this estimation was trivial, andthis method ensured that the best sprint performance for eachindividual was used consistently. Second, there was a temporal separation between the performance (i.e., SBE100) and thelaboratory morphology and strength measurements within thisstudy. Although this is clearly a potential confounder thatmight have reduced the strength of the effects we have observed, the continuity of training in the sprint groups would
have reduced the likelihood of large differences in muscle volume or strength between the dates of laboratory assessment
and the sprint performance. Third, it may be argued that theuse of isometric force lacks specificity in relation to sprint
running (39), where the joint angular velocities can be very
high (e.g., knee extension at ~850°·s−1 [1]). However, theaim of the current study was to accurately assess the isolated
strength of five distinct functional muscle groups (i.e., individual joint torques), given the paucity of data on the function, and particularly comparative strength, of these muscle
groups in sprinters versus controls. Isometric measurements
are also known to be highly reliable, sensitive, and relatively
easy to conduct and also require limited familiarization time(36). In contrast performing these isolated muscle groupmeasurements dynamically, especially at high velocity, ina consistent and reliable manner would be highly challenging. Finally, the cross-sectional nature of this study meansthat definitive cause and effect relationships remain unknown. However, on the basis of the pronounced differences and relationships we have observed, and the logicalrationale for the importance of the muscle groups (hip extensors and knee flexors) and individual muscles (gluteus
maximus) identified, it seems likely that there is a large
causal component to these relationships.
Practical summary and implications. The extensive
differences in muscle morphology between elite and sub-elite
sprinters and the strength of the relationships we have observed have clear implications for coaches and practitioners.

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momentum from down and back at the end of stance, to upward and forward during swing, and therefore may be important for early swing phase mechanics and thus sprint
performance (5,25).
Furthermore, strong relationships were observed between
the SBE100 and the relative muscle volume of the hip extensor(r = −0.560) and knee flexor (r = −0.522) muscle groups, andspecifically in only one individual muscle (gluteus maximus
r = −0.580). Consequently, separate regression analyses formuscle groups and individual muscles revealed that the relative volume of the hip extensors explained 31.4% and gluteus
maximus 33.6% of the variance in sprint performance, respectively. During sprint running, the gluteus maximus isactivated from late swing phase to midstance (26), accelerating the leg underneath the body (34) and making a major
contribution to the generation of propulsive forces alongwith the hamstring muscles (26,35). Thus, greater gluteus
maximus volume would be expected to facilitate greater propulsion forces and, therefore, greater sprinting speeds. It is interesting that the gluteus maximus, the largest individual
muscle in the human body, appears to be particularly importantfor fast running. The biologically expensive process of developing a large gluteus maximus represents a significant evolutionary investment that presumably confers an advantage forsurvival. It is possible that the role of the gluteus maximus
in facilitating humans to run fast explains the evolution of
the gluteus maximus as the largest muscle in the human body.
Isometric strength. The elite sprinters (absolute and relative 3/5 muscle groups [hip extensors and flexors, and knee
flexors] and sub-elite sprinters (absolute 2/5 [knee flexors
and extensors]; relative 5/5 muscle groups) were stronger thancontrols. Because of the observed sprint and resistance training history of the sprint groups, and their greater muscle volume, it is unsurprising that both sprint groups were found to
be stronger than controls in several muscle groups. Unexpected findings of this study were that no strength measurements for any muscle group were discriminatory between
sprint groups or negatively associated with sprint performance. This contrasts with previous research demonstratingthat measures of isokinetic hip flexion strength were related
to aspects of sprint performance (14). Furthermore, the speculated importance of hip extension and plantarflexion force during the stance phase (24,26) and hip flexion force duringswing phase (24,28) for fast running might also make the current results surprising. However, task/contraction specificity
may be an important factor influencing the association between
strength/power of the hip muscles and sprint performance (6).
Therefore, the findings of this study could be a consequenceof a lack of specificity between the isometric strength measures of the current study and the dynamic nature of sprint
running (36). It is acknowledged, however, that isometricstrength was only measured on one occasion and with no familiarization because of the difficulty in recruiting elite-level
sprinters for even a single assessment session. Although theprotocol was clearly the same for all three groups, this may
have introduced some noise into the data potentially, reducing

Although overall muscularity appeared important for performance (all muscles: absolute volume + 24% for elite vs subelite; performance correlations for absolute [r = −0.629] andrelative [r = −0.422] volume), this belied the fact that there
were highly variable and nonuniform effects for specific muscle groups and muscles. The largest muscle group–specific effects were found primarily for the hip extensors (differences of+32% absolute and +15% relative volume; explaining 47.5%[absolute volume] to 31.4% [relative volume] of the variability
in performance) and secondarily for the knee flexors (differences of +24% absolute volume; performance correlations
for absolute [r = −0.682] and relative [r = −0.522] volume),
whereas the plantarflexors showed no differences between
the sprint groups. This evidence strongly supports the idea thatdeveloping large hip extensors and knee flexors, for example,
through resistance training, would be valuable for the sprint
athlete looking to enhance performance (27).
For absolute muscle volumes, very similar factors differentiated both sub-elite sprinters from controls as well as elite versus sub-elite sprinters (e.g., total muscle volume, four muscle
groups in the same order of magnitude, and five individual
muscles; see Table, Supplemental Digital Content 2, A summary table of the observed significant differences between
sub-elite sprinters vs controls, and elite sprinters vs sub-elite
sprinters, http://links.lww.com/MSS/C151), indicating that the
progressive development of these same variables may continuously improve performance up to elite level. By contrast, forrelative volumes, although a wide range of factors distinguished sub-elite sprinters from controls, elite sprinters weredifferentiated by only four variables (volume of the hip extensor muscle group, TFL, sartorius, and gluteus maximus), indicating that a more targeted development may be needed for
elite performance. Moreover, the need for targeted hypertrophy even within muscle groups is emphasized by the individual muscle findings with three muscles being larger in elite vssub-elite sprinters in both absolute and relative terms (TFL:
absolute, +57%; relative, +37%; sartorius: absolute, +47%;
relative, +28%; gluteus maximus: absolute, +45%; relative,+25%) with the gluteus maximus alone explaining 33.6% (relative volume) to 43.8% (absolute volume) of the variance inperformance among sprinters. However, our knowledge of theexercises needed to facilitate hypertrophy of these individual
muscles (TFL, sartorius, and gluteus maximus) is relatively limited. Given the greater sprint training experience of the elitegroup in this study, it is also possible that regular, prolonged
sprint training may stimulate many of the morphological characteristics we have observed (40).

CONCLUSION
In conclusion, this investigation highlights for the first timethe importance of highly inhomogeneous muscularity, with a
specific pattern of distribution for elite sprint running performance compared with sub-elite sprinters and controls. Specifically, this experiment revealed for the first time that the hip
extensors of elite sprinters were of a greater absolute and relative size and both these measurements were related to performance, such that hip extensor absolute volume explained
47.5% of the variability in sprint running performance. Individual muscles showed particularly pronounced differencesin the muscle distribution of elite sprinters, with three hip muscles (TFL, sartorius, and gluteus maximus) consistently larger
in absolute and relative terms, and the absolute volume of thegluteus maximus alone explained 43.8% of the variance insprint performance. Based on this novel evidence, it is therefore recommended that coaches and athletes be attentive tothe development of muscle volume in these specific lower
body muscles to enhance sprint running performance.
This investigation was financially supported by the UK Athletics andthe UK Strength and Conditioning Association. The authors thank theparticipants who gave their time to take part in this research study,
Dr. Bill Haug for his help with data analysis, and Mr. Sam Power forhis significant contribution and support in data acquisition.
No conflicts of interest are relevant to this article. The present results
do not constitute endorsement by the American College of Sports
Medicine, and the authors declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

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