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Greater Hamstrings Muscle Hypertrophy but
Similar Damage Protection after Training at
Long versus Short Muscle Lengths
SUMIAKI MAEO
1
, MENG HUANG
2
, YUHANG WU
2
,HIKARUSAKURAI
2
, YUKI KUSAGAWA
2
,
TAKASHI SUGIYAMA
3
, HIROAKI KANEHISA
2
,andTADAOISAKA
2
1
Research Organization of Science and Technology, Ritsumeikan University, Kusatsu, Shiga, JAPAN;
2
College of Sport and
Health Science, Ritsumeikan University, Kusatsu, Shiga, JAPAN; and
3
Ritsumeikan Global Innovation Research Organization,
Ritsumeikan University, Kusatsu, Shiga, JAPAN
ABSTRACT
MAEO, S., M. HUANG, Y. WU, H. SAKURAI, Y. KUSAGAWA, T. SUGIYAMA, H. KANEHISA, and T. ISAKA. Greater Hamstrings
Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths. Med. Sci. Sports Exerc.,Vol.53,
No.4,pp.825–837, 2021. The biarticular hamstrings are lengthened more in a seated (hip-flexed) than prone (hip-extended) position. Purpose:
We investigated the effects of seated versus prone leg curl training on hamstrings muscle hypertrophy and susceptibility to eccentric
exercise-induced muscle damage. Methods: Part 1: Twenty healthy adults conducted seated leg curl training with one leg (Seated-Leg)
and prone with the other (Prone-Leg), at 70% one-repetition maximum (1RM), 10 repetitions per set, 5 sets per session, 2 sessions per week
for 12 wk. Magnetic resonance imaging (MRI)–measured muscle volume of the individual and whole hamstrings was assessed pre- and
posttraining. Part 2: Nineteen participants from part 1 and another 12 untrained controls (Control-Leg) performed eccentric phase-only leg curl
exercise at 90% 1RM, 10 repetitions per set, 3 sets for each of the seated/prone conditions with each leg. MRI-measured transverse relaxation time
(T
2
) and 1RM of seated/prone leg curl were assessed before, 24, 48, and 72 h after exercise. Results: Part 1: Training-induced increases in muscle
volume were greater in Seated-Leg versus Prone-Leg for the whole hamstrings (+14% vs +9%) and each biarticular (+8%–24% vs +4%–19%),
but not monoarticular (+10% vs +9%), hamstring muscle. Part 2: After eccentric exercise, Control-Leg had greater increases in T
2
in each hamstring
muscle (e.g., semitendinosus at 72 h: +52%) than Seated-Leg (+4%) and Prone-Leg (+6%). Decreases in 1RM were also greater in Control-Leg (e.g.,
seated/prone 1RM at 24 h: −12%/−24%) than Seated-Leg (0%/−3%) and Prone-Leg (+2%/−5%). None of the changes significantly differed between
Seated-Leg and Prone-Leg at any time points. Conclusion: Hamstrings muscle size can be more effectively increased by seated than prone leg curl
training, suggesting that training at long muscle lengths promotes muscle hypertrophy, but both are similarly effective in reducing suscepti-
bility to muscle damage. Key Words: HAMSTRINGS, BI- AND MONOARTICULAR MUSCLES, MUSCLE VOLUME, T
2
Strengthening the hamstrings is thought to improve
sprint performance (1) and reduce the risk of hamstring
strain injury (2), therefore giving benefits to many
athletes and sports enthusiasts. The single-joint knee flexion
(“leg curl”) is one of the most common exercises to train the
hamstrings because it isolates the target muscles by using a
weight machine, which stabilizes the body and prevents exces-
sive joint movement (3,4). In fact, there is considerable evi-
dence that single-joint leg curl training can increase strength
and size of the hamstrings (5–7).
The leg curl can be performed inseated and prone positions,
between which there is a marked difference in the hip joint an-
gle, therefore the muscle lengths of the hamstrings. Namely,
because of the biarticular nature of three out of four hamstring
muscles, they are lengthened more in the seated (hip-flexed)
than prone (hip-extended) position (8–10) (Fig. 1). Some stud-
ies (11–13) reported that training-induced muscle hypertrophy
was greater when trained at long versus short muscle lengths,
but others (14–16) did not find a statistically significant differ-
ence. This discrepancy seems at least partly due to relatively
small sample sizes (n=8–13 per condition) (11–16) and/or
short intervention periods (6–8 wk) (11–14,16) of these stud-
ies. Importantly, the previous studies all adopted isometric
(11,12,14,15) or partial range of motion (13,16) training at
Address for correspondence: Sumiaki Maeo, Ph.D., Research Organization of
Science and Technology, Ritsumeikan University, 1-1-1, Nojihigashi, Kusatsu,
Shiga 525-8577, Japan; E-mail: smaeo1985@gmail.com.
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 versions
of this article on the journal’s Web site (www.acsm-msse.org).
0195-9131/20/5304-0825/0
MEDICINE & SCIENCE IN SPORTS & EXERCISE
®
Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc.
on behalf of the American College of Sports Medicine. This is an
open-access article distributed under the terms of the Creative Commons
Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND),
where it is permissible to download and share the work provided it is properly
cited. The work cannot be changed in any way or used commercially without
permission from the journal.
DOI: 10.1249/MSS.0000000000002523
825
APPLIED SCIENCES
different joint angles about the samejoint to compare long ver-
sus short muscle length conditions (e.g., knee flexed vs ex-
tended positions to train the quadriceps). However, it is generally
recommended that resistance training be performed with full
range of motionfor general fitness (4) and muscle hypertrophy
(17). Thus, exploring the effect of seated versus prone leg curl
training, performed with full range of motion, on hamstrings
muscle hypertrophy would be useful from both basic research
and applied points of view.
Although it is challenging to test the protective effect of any
kind of interventions against muscle strain injury that is multi-
factorial, some insights can be gained by examining its effect
on susceptibility to exercise-induced muscle damage, which
manifests as decreased muscle function and muscle swelling/
edema (18). Both muscle damage and strain injury are trig-
gered by eccentric contractions, and it is suggested that there
is a link between susceptibility to damage and likelihood of
strain injury (19,20). Eccentric exercise-induced muscle dam-
age is known to be mitigated by performing priming exercise,
with a greater effect conferred when the exercise had been per-
formed at long versus short muscle lengths (21). Thus, it is en-
visaged that the protective effect against muscle damage
would be greater for seated versus prone leg curl training,
but this has never been investigated.
The purpose of this study was to examine the effects of
seated versus prone leg curl training on hamstrings muscle
hypertrophy and susceptibility to eccentric exercise-induced
muscle damage. To this end, we designed a two-part study. Part
1 involved intervention of seated versus prone leg curl training.
Subsequently in part 2, eccentric exercise was performed by
those who had undergone part 1 as well as by another cohort
of untrained controls to examine the effectiveness of the previous
seated and prone leg curl training on preventing muscle damage.
The primary measures of this study were MRI-measured mus-
cle volume for part 1 and transverse relaxation time (T
2
)for
part 2 to evaluate training-induced muscle hypertrophy and
exercise-induced muscle edema of each hamstring muscle, re-
spectively. Because hamstring strain injuries most commonly
occur in the biceps femoris long head (BFL) and secondly in
the semitendinosus (ST) muscles, often at their musculotendinous
junctions (22,23), these muscles and regions were analyzed in
detail. We hypothesized that 1) hypertrophic effects would be
greater for the seated than prone leg curl training and 2) pro-
tective effects would also be greater for the seated than prone
leg curl training.
METHODS
Study Design and Participants
This study was approved by the Ethics Committee of
Ritsumeikan University (BKC-IRB-2018-087) and consisted
of two parts: training intervention (part 1) and eccentric exercise
FIGURE 1—Operating ranges of each hamstring muscle on the n ormalized force–length curve during the seated and proneknee flexion (leg curl) exercise.
These were calculated using the OpenSim Lower Limb model (8,9), with the hip joint angle at 90° and 30° for the seatedand prone conditions, respectively,
and the knee joint angle ranging from 0° to 90° for both conditions as conducted in this study. It is clearly seen that the three biarticular hamstrings (BFL,
ST, and SM) operate at longer muscle lengths during the seated than prone condition, while there is no difference in the monoarticular BFS. Some differ-
ences within the biarticular muscles are likely due to their different musculotendinous architecture and moment arms (10).
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(part 2) (Fig. 2). In part 1, 20 young adults conducted 12-wk
unilaterallegcurltraininginaseatedpositionwithoneleg
(Seated-Leg) and in a prone position with the other leg
(Prone-Leg). After the intervention, 19 participants from part
1 and another 12 young adults as untrained controls (Control-
Leg) performed unilateral eccentric phase-only leg curl exercise
in each of the seated and prone positions with each leg in part 2.
One participant from part 1 did not attend part 2 due to an un-
related reason to this study. Participants were recruited by con-
venience sampling for attending both part 1 and part 2 or only
part 2 depending on their schedule availability (Fig. 2), until
the sample sizes for each condition/leg reached about 20.
The participants were all healthy, but none had been involved
in any type of systematic resistance training program in the
past 12 months. Written informed consent was obtained from
each participant.
Part 1
Training program. Each leg was randomly assigned to
Seated-Leg or Prone-Leg, with the dominant and nondominant
legs counterbalanced by the use of a computer-generated list.
Both legs were trained unilaterally with the assigned training
condition, by using a modified (a backrest inserted) seated leg
curl machine (Pro 2 Series, Life Fitness, Chicago, IL) with the
hip joint fixed at ~90° and a prone leg curl machine (Toredo,
Senoh, Japan) with the hip joint fixed at ~30° (0° = anatomical
position). The knee joint range of motion was 0°–90° for both
conditions, which we defined as the full range of motion to
standardize it among participants and between conditions/
legs. Adjustable straps were tightly fastened across the pelvis
to prevent extraneous movement. Individualized machine set-
tings (i.e., joint and seat positions) were kept the same
throughout the study for each participant.
Each training session commenced with 5–10 warm-up rep-
etitions at 50% of the load prescribed for that session (detailed
below) with the assigned training condition. Participants then
performed the seated or prone leg curl 10 repetitions per set
for 5 sets, taking 2 s for each of the concentric (knee flexing)
and eccentric (knee extending) phases without a pausing phase
with the guide of a metronome (60 bpm). Two-minute rest in-
tervals were taken in between sets. After training one leg (5
sets), the other leg was trained. The preceding leg was
counterbalanced in the first training session among participants,
and it was switched every session for each participant. Training
was conducted twice per week, separated by ≥~48 h. Training
load was gradually increased at the first, second, and third ses-
sions from 50%, 60%, and 70% of one-repetition maximum
(1RM) measured pretraining (detailed below), respectively,
and 70% of 1RM was used thereafter. At least one examiner
FIGURE 2—Flow diagram and demographic information of participants.
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always supervised the training sessions and provided verbal
encouragement and also corrected the joint positions and/or
movement speed of the exercise when necessary. The exam-
iners also assisted (spotted) the participants in executing the
exercise when they could no longer repeat the repetitions up
to 10 in each set. This was done in such a way that the partici-
pants could complete the task in a controlled manner with their
continuous (~maximum) efforts, which accounted for 20% of
all repetitions (typically in the final 1–2setswithinasession).
If the participants could complete all of the prescribed protocol
at the third session and thereafter without examiners’assist,
+5% of 1RM was added at the subsequent sessions.
Measurements. All participants attended three measure-
ment sessions; two sessions before the training period (Pre-TR
1 and Pre-TR 2) separated by 2–7d(≥~72 h) and one session
after the training period (Post-TR) 2–4 d after the final training
session. Participants were instructed to avoid any intensive
and unfamiliar physical activities within 2 d before Pre-TR 1
and throughout the experimental period. The following vari-
ables were measured.
1RM. 1RM was measured in each leg with the assigned
training condition using the same machines as for the training.
At Pre-TR 1, participants were familiarized with the exercise
by performing 3–5 repetitions with a light load, which was
gradually increased (three to five stages) with a short rest pe-
riod (10–20 s) until the participants felt it somewhat heavy.
Thereafter, only 1 repetition was performed at each increasing
load by increments of 2.0 kg and 1.7 kg for the seated and
prone leg curl, respectively, with ≥2 min rest in between trials.
1RM was defined as the maximum load lifted with the proper
joint positions, which was checked by the examiner(s). At
Pre-TR 2, participants performed 5, 3, and 1 warm-up repeti-
tions at 50%, 75%, and 90% of 1RM of Pre-TR 1, respec-
tively, with 30 s rest, and tried the same 1RM load of
Pre-TR 1 after ≥2 min rest. 1RM was determined by increasing
or decreasing the load thereafter. At Post-TR, the warm-up and
the 1RM assessment were similarly conducted but based on
the 1RM of Pre-TR 2. The training load and its increments
in the training sessions described above were also based on
the 1RM of Pre-TR 2. The mean within-participant coefficient
of variation between the two pretraining sessions was 6.8%
and 3.4% for the seated and prone 1RM, respectively.
T
1
-MRI. Preceding the 1RM measurement, longitudinal re-
laxation time (T
1
)–weighted cross-sectional MRI scans of
the thigh were obtained for each leg using body array and
spine coils (Body 18 and CP Spine Array Coil; Siemens
Healthineer, Erlangen, Germany) with the following parame-
ters: field of view, 200 200 mm; matrix, 512 512; slice
thickness, 5 mm; voxel size, 0.39 0.39 5 mm; in-plane res-
olution, 0.39 mm; TR, 700 ms; TE, 10 ms; flip angle, 120°;
number of channels, 1; gap, 5 mm; number of slices, 21 3
blocks (Fig. 3). Participants lay supine with their legs extended
and muscles relaxed in a 3-T magnet bore (MAGNETOM
Skyra, Siemens Healthineer). To obtain cross-sectional images
at the same positions throughout the study within each partici-
pant, the following steps were taken: 1) by using coronal
localizer images, the thigh length was measured as the dis-
tance between the greater trochanter and the distal end of the
FIGURE 3—Example images for the T
1
-weighted MRI scans (for Seated-Leg in part 1) and T
2
-weighted MRI scans (for Control-Leg in part 2) at 50% of
the thigh length, and a coronal localizer image. The images shown here are all for the right leg, but both legs were scanned in both part 1 and part 2.
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femur, 2) the center slice of a block of 21 slices (i.e., the 11th)
was set at 50% of the thigh length, 3) the block was then moved
proximally with the fixed 5-mm slice gap/increment until the
most proximal slice was set at slightly above the ischial tuberos-
ity (i.e., the origin for the biarticular hamstrings), and 4) 3 se-
ries of blocks were taken to cover the whole hamstrings (WH).
Images were analyzed by using image analysis software
(Horos, Horos Project), with the MRI data anonymized and in-
vestigators blinded to the training conditions. Anatomical
cross-sectional areas (ACSA) of the individual hamstring
muscles (i.e., BFL, ST, semimembranosus [SM], and biceps
femoris short head [BFS]) were manually outlined in every
other image from the most proximal to the most distal image
in which the muscle was visible. In addition, the gracilis
(GRA) and sartorius (SAR) muscles, which also work as knee
flexors located in the thigh, were analyzed in the same manner
as above. Because the origin for the SAR is the anterior supe-
rior iliac spine, the most proximal parts of this muscle were not
fully covered in this study. Thus, the SAR was analyzed from
the image at the ischial tuberosity to the most distal image in
which this muscle was visible. Care was taken to exclude vis-
ible adipose and connective tissue incursions. ACSA for the
skipped images and gaps was estimated based on linear inter-
polation between the images in which ACSA was outlined
(24). The volume of individual muscle was determined by
summing all ACSA for that muscle multiplied by the slice
thickness.The WH volume was calculated by summing the in-
dividual muscle volumes of the four hamstring muscles. To
explore the effects of seated versus prone leg curl training on
muscle hypertrophy at the most commonly injured locations
within the hamstrings, changes in ACSA of the BFL and ST
at 30% (proximal) and 70% (distal) of the thigh length were
measured using the nearest slices to these locations (named
as BFL
Proximal
,BFL
Distal
, etc.). The mean within-participant
coefficient of variations between the two pretraining sessions
for the muscle size measures were as follows: muscle volume
of the WH, 1.4%; BFL, 1.6%; ST, 1.7%; SM, 1.4%; BFS,
2.1%; GRA, 1.4%; SAR, 1.5%; ACSA of the BFL
Proximal
,
5.2%; BFL
Distal
,5.2%;ST
Proximal
,2.1%;ST
Distal
,4.0%.
Part 2
Eccentric exercise. Using the same leg curl machines as
above, participants performed unilateral eccentric phase-only
leg curl exercise at 90% of 1RM (detailed below), 10 repeti-
tions per set, 3 sets in each of the seated and prone conditions
(6 sets in total) with each leg (18). During these exercises, the
examiner(s) moved (pushed/lifted) the load to the starting po-
sition (knee joint, 90°), and the participants moved the load to
the finish position (knee joint, 0°) by performing eccentric
contractions of the knee flexors in a controlled manner over
a 2-s count with the guide of a metronome. Two-second
between-repetition intervals were taken, during which the load
was moved back to the starting position by the examiner (18).
After completing 1 set with one leg in either the seated or the
prone condition, the order of which was counterbalanced
among participants, the other leg performed the same eccentric
exercise (based on its 1RM) with a 1-min interval. Thiswas re-
peated until each leg performed 3 sets. After a rest period of
5 min, participants then performed the eccentric exercise in
the other condition. Participants familiarized themselves with
the eccentric exercise using a light load (5 repetitions with
~50% of 1RM) and took at least 2 min rest before conducting
the actual eccentric task.
Measurements. Before (Pre-ECC) and 24, 48, and 72 h
after (Post-ECC 24–72) the eccentric exercise, 1RM and
MRI-measured T
2
were assessed as indices of muscle damage
markers (18,25). The Pre-ECC measurement in part 2 was in-
cluded in the Post-TR measurement in part 1 for those who
underwent both parts. Measurements were conducted as
follows.
1RM. 1RM was assessed in the same manner as described
in part 1, but in both seated and prone conditions with each leg
in part 2. Briefly, the seated or prone leg curl 1RM was
assessed in each leg after a warm-up, alternatively between
legs with 1-min intervals (i.e., ≥2 min rest for the same leg).
Orders of the conditions and legs were counterbalanced
among participants. After assessing 1 RM in the preceding
condition, participants took at least 2 min rest and proceeded
to the other condition.
T
2
-MRI. T
2
-weighted MRI scans for both thighs were con-
ducted using the same device described above, with the fol-
lowing parameters: field of view, 450 450 mm; matrix,
256 256; slice thickness, 4 mm; voxel size, 1.76 1.76 4 mm;
in-plane resolution, 1.76 mm; TR, 2000 ms; TE, 10 increments
from 10 to 100 ms; flip angle, 180°; number of channels, 1;
gap, 12 mm; number of slices, 15 1 block (Fig. 3). The thigh
length was measured as described above, and the center slice
of a block of 15 slices (i.e., the 7th) was set at 50% of the thigh
length. One block of T
1
-weighted MRI scans, centered at the
50% of the thigh length, was also taken for each thigh with
the parameters described in the part 1 section, which was used
as a guide to outline the ACSA of each hamstring muscle in
T
2
images. Images were analyzed using Osirix Lite software
(Pixmeo, Geneva, Switzerland). Regions of interest for each
of the four hamstrings were outlined at 50% of the thigh
length (18). The BFL and the ST were additionally analyzed
at 30% and 70% of the thigh length using the nearest slices to
these locations (but only for two time points of Pre-ECC and
Post-ECC 72 h). T
2
relaxation time was calculated by least
squares analysis fitting the signal intensity at each of the 10
echo times (n10 ms: 10 to 100 ms at 10 incremental steps)
to a monoexponential decay using the following equation:
Sn¼S0exp −TEn=T2ðÞ
n¼10 to 100 ms at 10 incremental stepsðÞ
where TE is echo time, S
0
is signal intensity at 0 ms, and S
n
is
signal intensity at TE
n
.
Statistical analysis. All data were analyzed using SPSS
software (version 25; IBM Corp, USA) unless otherwise
noted. Statistical significance was set at P< 0.05. For part 1,
data from the two pretraining sessions were averaged and used
for further analysis as Pre-TR values. An ANCOVA was used
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to compare changes in muscle size measures (volume and
ACSA) between Seated-Leg and Prone-Leg, with the Pre-TR
values as covariates and the Post-TR values as the dependent
variables. A linear mixed-effects model was used with a sub-
ject as a random effect and a leg (training condition) as a fixed
effect. Because the 1RM in part 1 was measured under the dif-
ferent conditions between the legs (i.e., seated 1RM or prone
1RM), the Post-TR values were z-scored using the Pre-TR
mean and SD for each condition [i.e., the z-score = (individual
Post-TR value –Pre-TR mean)/Pre-TR SD] and were compared
between the legs by a paired t-test. For part 2, a one-way
ANCOVA was used to compare changes in muscle damage
indices (T
2
and 1RM) between Seated-Leg, Prone-leg, and
Control-Leg, with the Pre-ECC values as covariates and the
values at each of the Post-ECC time points as the dependent
variables. A general linear model with a least significant dif-
ference (LSD) post hoc test was used. Residuals were checked
for normality and homoscedasticity by Shapiro–Wilk’stest
and Levene’s test, respectively, and some data sets for T
2
and 1RM in part 2 were rejected by both or either of these.
However, the main statistical results were the same when these
data sets were analyzed with either an ANCOVA or equiva-
lent nonparametric test (rank-transformed values [Quade’s
test]). Thus, all results are shown as those based on ANCOVA
with raw values (except for z-score s in 1RM for part 1) for
ease of interpretation. Finally, to improve statistical inference,
mean difference from baseline on raw data with their bootstrap
95% confidence interval (CI) was calculated by using estima-
tion statistics (26). Detailed descriptive and test statistics are
provided in Supplemental Digital Contents.
RESULTS
Part 1
Muscle volume. There were significant differences in
mean muscle volume change between the legs in each of the
WH, BFL, ST, SM, and SAR (P≤0.010), but not in the
BFS (P=0.190)andGRA(P= 0.097) (Fig. 4; see Table for
details, Supplemental Digital Content 1, Muscle volume
before and after leg curl training, http://links.lww.com/MSS/
C152). The increases in muscle volume were greater for
Seated-Leg than Prone-Leg in the WH (ANCOVA- adjusted
mean change: +14.1% vs +9.3%), BFL (+14.4% vs +6.5%),
ST (+23.6% vs +19.3%), and SM (+8.2% vs +3.6%). By
contrast, the change in the SAR was smaller for Seated-Leg
than Prone-Leg (+7.8% vs +11.8%).
FIGURE 4—Changes in muscle volume for Seated-Leg and Prone-Leg after training. Data are plotted as individual raw change (Δ) values from baseline
(small dots), with a group mean (larger dots) and its 95% CI (indicated by the ends of the vertical error bars) shown together. The CI and the bootstrap
sampling distributions (5000 samples, bias-corrected and accelerated) were obtained from respective paired (pre- to posttraining) data. *Significant differ-
ence between legs at P< 0.05 based on a baseline-adjusted ANCOVA. n= 20 legs for both Seated-Leg and Prone-Leg. The bar graphsin the summary figure
are based on the mean changes for each muscle.
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ACSA. Changes in ACSA of the BFL and ST at the prox-
imal and distal regions were significantly different between
the legs in the BFL
Proximal
(+20.8% vs +8.7%), BFL
Distal
(+10.7% vs +5.4%), and ST
Proximal
(+28.2% vs +21.1%), all
showing greater increases for Seated-Leg than Prone-Leg
(P= 0.002–0.039), but not in the ST
Distal
(+21.4% vs +17.0%,
P= 0.107) (Fig. 5; see Table for details, Supplemental Digital
Content 2, ACSA before and after leg curl training, http://
links.lww.com/MSS/C153).
1RM. Changes in 1 RM as z-scores did not differ between
Seated-Leg and Prone-Leg (0.81 ± 1.25 vs 0.76 ± 1.14,
t
19
=0.442,P= 0.663). The mean ± SD values and the mean
changes were as follows: Seated-Leg: Pre-TR = 40.9 ± 15.7 kg,
Post-TR = 53.6 ± 19.6 kg, +31.1%; Prone-Leg: 23.9 ± 8.3 kg,
30.3 ± 9.5 kg, +26.6%.
Part 2
T
2
.T
2
changes at the mid-thigh were more prominent at
Post-ECC 72 h than Post-ECC 24–48 h for all hamstrings,
so only the data for Post-ECC 72 h are shown in Figure 6,
and those for Post-ECC 24–48 h are available in a supplement
(see Table/Figure for details, Supplemental Digital Content 3,
T
2
before and after eccentric exercise, http://links.lww.com/
MSS/C154). A one-way ANCOVA revealed significant dif-
ferences in mean T
2
change between the legs at Post-ECC
FIGURE 5—Changes in ACSA of the BFL and ST at 30% (BFL
Proximal
,ST
Proximal
) and 70% (BFL
Distal
,ST
Distal
) of the thigh length for Seated-Leg and
Prone-Leg after training. Data are plotted as individual raw change (Δ) values from baseline (small dots), with a group mean (larger dots) and its 95%
CI (indicated by the ends of the vertical error bars) shown together. The CI and the bootstrap sampling distributions (5000 samples, bias-corrected and
accelerated) were obtained from respective paired (pre- to posttraining) data. *Significant difference between legs at P< 0.05 based on a baseline-adjusted
ANCOVA. n= 20 legs for both Seated-Leg and Prone-Leg. The bar graphs in the summary figure are based on the mean changes for each muscle.
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72 h in each hamstring muscle at the mid-thigh (Fig. 6). The
changes in T
2
at Post-ECC 72 h were greater (P≤0.035) for
Control-Leg than Seated-Leg and Prone-Leg in each of the
BFL (+3.8% vs +0.3% vs +0.4%), ST (+56.9% vs +2.0% vs
+5.7%), SM (+3.0% vs −1.8% vs −0.7%), and BFS (+5.5%
vs +0.6% vs +0.1%). The T
2
changes in the ST at 48 h were
also greater (P≤0.002) for Control-Leg than Seated-Leg
and Prone-Leg (+26.9% vs +2.6% vs +4.4%), and those in
the SM at 24 h were greater (P= 0.004) for Control-Leg than
Seated-Leg (+2.4% vs −1.1%) but not than Prone-Leg
(+0.5%, P= 0.103). There were no significant differences be-
tween Seated-Leg and Prone-Leg in all muscles at any time
points (P≥0.210).
At the proximal and distal regions of the BFL and ST, T
2
changes at Post-ECC 72 h were significantly (P≤0.046) dif-
ferent between the legs (Fig. 7; see Table for details,
Supplemental Digital Content 4, T
2
changes at the proximal/
distal thigh, http://links.lww.com/MSS/C155). The changes
at the BFL
Proximal
were greater for Control-Leg than
Seated-Leg (+6.5% vs +1.1%, P= 0.019) but not than
Prone-Leg (+2.6%, P= 0.090). Similarly, those at the
BFL
Distal
were significantly greater for Control-Leg than
Seated-Leg (+4.8% vs +1.4%, P= 0.030) but not than
Prone-Leg (+1.8%, P=0.052).BothST
Proximal
(+59.2% vs
+4.2% vs 8.5%) and ST
Distal
(+39.6% vs +6.1% vs 5.1%)
had greater T
2
changes for Control-Leg than Seated-Leg and
FIGURE 6—Changes in T
2
of each hamstring muscle at 50% of the thigh length (BFL
Middle
,ST
Middle
,SM
Middle
,BFS
Middle
) at 72 h after eccentric exercise
for Seated-Leg, Prone-Leg, and Control-Leg. Data are plotted as individual raw change (Δ) values from baseline (small dots), with a group mean (larger
dots) and its 95% CI (indicated by the ends of the vertical error bars) shown together. The CI and the bootstrap sampling distributions (5000 samples,
bias-corrected and accelerated) were obtained from respective paired (pre- to postexercise) data. *Significant difference between legs at P<0.05based
on a baseline-adjusted ANCOVA and an LSD post hoc test. n= 19 legs for both Seated-Leg and Prone-Leg, and 24 legs for Control-Leg. The bar graphs
in the summary figure are based on the mean changes for each muscle.
http://www.acsm-msse.org832 Official Journal of the American College of Sports Medicine
APPLIED SCIENCES
Prone-Leg (P< 0.001). No significant differences were found
between Seated-Leg and Prone-Leg (P≥0.515).
1RM. A one-way ANCOVA found significant (P≤0.005)
differences between the legs in each of the seated 1RM and
prone 1RM at all Post-ECC time points (Fig. 8; see Table
for details, Supplemental Digital Content 5, 1RM before and
after eccentric exercise, http://links.lww.com/MSS/C156). The
changes in 1RM were greater for Control-leg than Seated-Leg
and Prone-Leg at all time points for both seated 1RM and
prone 1RM (P≤0.011), without any significant differences
between Seated-Leg and Prone-Leg (P≥0.351).
DISCUSSION
The main findings of this study were that 1) hamstrings
muscle hypertrophy was clearly greater after the seated than
prone leg curl training, but 2) there was no evidence for the
superiority of the seated over prone leg curl training in
preventing muscle damage. Thus, although our first hypoth-
esis was supported, the second hypothesis was not. These re-
sults suggest that hamstrings muscle size can be more
effectively increased by seated than prone leg curl training,
while both are similarly effective in reducing susceptibility to
muscle damage.
FIGURE 7—Changes in T
2
of the BFL and ST at 30% (BFL
Proximal
,ST
Proximal
) and 70% (BFL
Distal
,ST
Distal
) of the thigh length at 72 h after eccentric ex-
ercise for Seated-Leg, Prone-Leg, and Control-Leg. Data are plotted as individual raw change (Δ) values from baseline (small dots), with a group mean
(larger dots) and its 95% CI (indicated by the ends of the vertical error bars) shown together. The CI and the bootstrap sampling distributions (5000 sam-
ples, bias-corrected and accelerated) were obtained from respective paired (pre- to postexercise) data. *Significant difference between legs at P<0.05based
on a baseline-adjusted ANCOVA and an LSD post hoc test. n= 19 legs for both Seated-Leg and Prone-Leg, and 24 legs for Control-Leg. The bar graphs in
the summary figure are based on the mean changes for each muscle.
SEATED VS PRONE LEG CURL TRAINING Medicine & Science in Sports & Exercise
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833
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Muscle hypertrophy. The changes in the WH volume
observed in this study (Seated-Leg: +14.1%, Prone-Leg:
+9.3%) were in the range of the values reported in previous
studies (+5.8–16.4%) (5,6) that conducted leg curl training
for the same duration (12 wk), although how it was performed
(i.e., seated or prone) was not specified in these studies. In either
case, it seems that typical hamstrings muscle hypertrophy was
induced by both training modalities conducted in this study.
What this study further adds is that the training-induced
change in the WH volume was ~1.5-fold greater for Seated-Leg
than Prone-Leg, which is clearly attributable to the greater
changes in all biarticular hamstrings, but not the monoarticular
BFS, for Seated-Leg (Fig. 4). This supported our first hypoth-
esis and indicates that only the biarticular hamstrings that were
in more lengthened positions had greater hypertrophic responses
after the seated leg curl training.
In part 1, the GRA and the SAR were also analyzed. Al-
though these muscles are often overlooked in studies investi-
gating knee flexors, the degrees of their muscle hypertrophy
found in this study (Fig. 4), particularly those of the GRA,
highlight their important roles as synergists in knee flexion
exercise. Thus, these muscles are worth more attention and
should be included as key synergists to the hamstrings in
future studies. Interestingly, while the changes in muscle
volume of the GRA did not statistically significantly differ
between the legs (P= 0.097 in favor of Seated-Leg), that
of the SAR was significantly greater for Prone-Leg than
Seated-Leg (Fig. 4). Although both the GRA and the SAR
are biarticular muscles that work as a knee flexor, the GRA
primarily works as a hip adductor located in the medial com-
partment of the thigh (also assists tibial internal rotation)
(27). This implies that the muscle length of the GRA is not
greatly influenced by whether the hip is at a flexed orextended
position (compared with the case for the biarticular ham-
strings). On the other hand, the SAR works as a hip flexor lo-
cated on the anterior thigh (28), indicating that the SAR is
lengthened more in a prone (hip-extended) than seated (hip-
flexed) position. These assumptions were supported by our
follow-up simulation analysis (see Figure, Supplemental Dig-
ital Content 6, Operating ranges for the GRA/SAR, http://
links.lww.com/MSS/C157). Thus, all of the six individual
muscles examined here consistently demonstrated that greater
hypertrophy occurred exclusively under the condition in
which the muscles were trained at long muscle lengths com-
pared with the other condition. Suggested mechanisms under-
pinning the greater hypertrophy include, but are not limited to,
greater muscle oxygen consumption (i.e., metabolic stress) (29)
and IGF-1 expression (13,30), both of which are thought to
FIGURE 8—Changes in the seated and prone leg curl 1RM at 24, 48, and 72 h after eccentric exercise for Seated-Leg, Prone-Leg, and Control-Leg. Data
are plotted as individual raw change (Δ) values from baseline (small dots), with a group mean (larger dots) and its 95% CI (indicated by the ends of the
vertical error bars) shown together. The CI and the bootstrap sampling distributions (5000 samples, bias-corrected and accelerated) were obtained from
respective paired (pre- to postexercise) data. *Significant difference between legs at P< 0.05 based on a baseli ne-adjusted ANCOVA and an LSD
post hoc test. n= 19 legs for both Seated-Leg and Prone-Leg, and 24 legs for Control-Leg. The bar graphs in the summary figure are based on the mean
changes for each 1RM measurement.
http://www.acsm-msse.org834 Official Journal of the American College of Sports Medicine
APPLIED SCIENCES
promote muscle hypertrophy (31), when exercised (13,29) or
fixed (30) at long versus short muscle lengths. Although we
do not have any data regarding potential mechanisms, our find-
ings on the differences in the hypertrophic responses between
the training conditions, and among muscles, should be useful
for future studies in examining training-induced hypertrophy
in relation to different exercise conditions.
It may be of clinical relevance that the BFL, the most com-
monly injured muscle within the hamstrings (22,23), had ~2.2-
fold greater hypertrophy for Seated-Leg than Prone-Leg in
muscle volume (Fig. 4), with similarly large (~2.0- to 2.4-fold)
differences between the legs also found at its vulnerable prox-
imal and distal regions (Fig. 5). This was also true for the sec-
ond most commonly injured ST in muscle volume and at its
proximal region, albeit smaller (~1.2–1.3-fold) differences be-
tween the legs. Although the difference at the distal ST was not
statistically significant (P= 0.107, Fig. 5), this may be partly be-
cause the degrees of muscle hypertrophy in the ST were overall
large for both legs (e.g., changes in muscle volume: ST, +23.6%
vs +19.3%; BFL, +14.4% vs +6.5%). Collectively, these re-
sults suggest that 1) muscle hypertrophy of the BFL is rela-
tively small after prone leg curl training but can be much
(~2.2-fold) promoted by seated leg curl training, and 2) the
ST responds (increases in size) well to both types of leg curl
training, with some further (~1.2-fold) effects achieved by
seated leg curl training.
Bourne et al. (32) in their recent review suggested that
knee-dominant (e.g., Nordic Hamstring and prone leg curl)
exercises seem to preferentially activate the ST, whereas
hip-dominant (e.g., hip extension and stiff-leg deadlift) exer-
cises appear to more heavily target the BFL and SM, based
on acute T
2
changes after exercise (which indicate muscle activa-
tion rather than damage [33]). In fact, Bourne et al. (34) reported
that 10 wk of Nordic Hamstring training increased the muscle
volume of the BFL, ST, SM, and BFS for ~6%, ~21%, ~5%,
and ~15%, respectively, and hip extension training increased
their volumes for ~12%, ~14%, ~8%, and ~10%, respectively
(Fig. 5 in [34]). The corresponding changes after our 12-wk
seated leg curl training were 14%, 24%, 8%, and 10% (10/
12 wk = 12%, 20%, 7%, and 8%), respectively. Thus, the
seated leg curl appears to induce significant hypertrophy
of not only the ST but also the BFL and SM, which is
unachievable through either the Nordic Hamstring or the hip
extension alone (34), while still inducing greater hypertrophy
in the ST than the other hamstrings. Although the response of
the BFS in this study seems somewhat lower compared with
those of Bourne et al. (34), we do not see this as a major
issue because 1) its size actually increased reasonably
(+10%) and 2) the biarticular hamstrings account for a major
portion of the WH in terms of size (87% in this study).
Therefore, although various types of exercises may be
necessary to comprehensively train the WH, performing the
seated leg curl may reduce the need for substantial volumes
of other hamstring exercises. Further research is warranted to
substantiate these issues. The current study could be used as
a foundation for such work.
Eccentric exercise-induced muscle damage. After
the eccentric exercise, Control-Leg had greater changes in
both T
2
and 1RM compared with Seated-Leg and Prone-Leg
at several time points, without significant differences between
Seated-Leg and Prone-Leg at any time points (Figs. 6−8). Al-
though some T
2
changes were significantly different only be-
tween Control-Leg and Seated-Leg (Fig. 7 and Supplemental
Digital Content 3, T
2
changes at the mid-thigh, http://links.lww.
com/MSS/C154), we do not take these as suggesting the
superiority of Seated-Leg over Prone-Leg because their 95% CI
of the mean changes mostly overlap with each other (and
P= 0.210–0.817). Overall, the results indicate that the seated
and prone leg curl training were similarly effective in reducing
susceptibility to muscle damage, which refuted our second
hypothesis. A previous study (21) reported that the protective
effect against muscle damage was greater when priming
exercise had been performed at long versus short muscle
lengths. However, their priming exercise was performed
only once (21), whereas the protective effect is known to
be cumulative (35–37). Collectively, it appears that priming
exercise at short and long muscle lengths can confer a similar
protective effect against muscle damage as long as sufficient
training stimulus was provided beforehand.
Within the hamstrings of Control-Leg, the ST exhibited
by far the most pronounced increases in T
2
among others
(Figs. 6–7). The largest T
2
increase in the ST is in line with
previous studies, which conducted similar eccentric leg curl
exercises and measured prolonged T
2
changes (38–40), and
also aligns with the abovementioned preferential activation/
hypertrophy in the ST after knee-dominant exercises (32,34).
It is not clear why the ST is prone to damage, but this may
be partly attributable to its unique morphology such as being
a fusiform muscle (41) and having high regional fiber length
heterogeneity (42,43). What is novel in this study is that such
damage in the ST based on the T
2
change was substantially
and similarly mitigated by both of the seated and prone leg
curl training (Figs. 6−7). We also found some evidence, albeit
to a weaker extent, for such protective effects in the other ham-
strings including the BFL. Whether this would translate into
prevention of muscle strain injury, however, is far from certain
as there are more differences than similarities between muscle
damage and strain injury (44). Further investigation with train-
ing intervention is warranted.
The protective effects were also evident from the 1RM changes,
where Control-Leg had greater decreases than Seated-Leg and
Prone-Leg over 72 h postexercise for both of the seated and
prone 1RM (Fig. 8). Interestingly, the decreases in Control-Leg
were apparently (~2–3-fold) larger for the prone than seated
1RM over 72 h post exercise (Fig. 8) although not statistically
tested. This would be consistent with shorter working muscle
lengths in the prone leg curl (Fig. 1), given that the optimum
angle is transiently shifted toward longer muscle lengths with
muscle damage (see Fig. 4 of [45]). Resistance training, espe-
cially eccentric training (46) or training at long muscle length
(14), has been shown to induce increases in fascicle length
(indicating serial sarcomere addition), which is reported to be
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835
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associated with lower risk of strain injury (47). Unfortunately,
we did not measure hamstring fascicle length, and it is beyond
the scope of this study to discuss its potential changes and influ-
ences on the main findings of this study (i.e., muscle hypertro-
phy and muscle damage). Future studies should be directed
toward adopting measurement techniques such as ultrasound
(48), diffusion tensor imaging (49), and/or microendoscopy
(50) for fascicle/sarcomere length measurements to further ex-
plore the effects of hamstring training intervention on its muscle
architecture and risk of strain injuries.
Limitations. There are some limitations to this study. For
part 1, although our findings on muscle hypertrophy strongly
suggest that muscle length during exercise is a key determi-
nant of resulting muscle hypertrophy, whether this is general-
izable to other training modalities is yet to be examined. From
an applied point of view, the approach of this study can be rep-
licated in other biarticular muscles such as the rectus femoris
as a knee extensor (with the hip joint extended vs flexed)
and the gastrocnemius as a plantarflexor (with the knee joint
extended vs flexed). From a viewpoint of muscle physiol-
ogy, it would be necessary to take into account influences/
interactions of the actual muscle lengths during exercise, as-
sociated joint moment arms, force exerted by the muscle,
and neural control (excitation) to seek for the mechanisms
behind greater muscle hypertrophy after training at long
versus short muscle lengths. For part 2, it is unknown if
the results would have been the same if we had used
heavier/more strenuous protocols to induce muscle damage.
We used a load of 90% 1RM with 6 sets (3 for each of the
seated/prone conditions) of 10 eccentric phase-only repeti-
tions, based on our previous study on the quadriceps (18).
On the other hand, Carmona et al. (38) used a similar protocol
but adopted a heavier load of 120% 1RM with 6 sets of 10
eccentric phase-only repetitions by the prone leg curl exercise
and found more severe symptoms of muscle damage than
those of this study. Thus, it is possible that adopting heavier/
more strenuous protocols may have resulted in different find-
ings, such as the one we secondly hypothesized. Further re-
search is needed to better understand the influence of muscle
length during resistance training on muscle hypertrophy and
susceptibility to muscle damage.
CONCLUSIONS
In summary, we demonstrated that hamstring muscle hyper-
trophy was greater after seated than prone leg curl training, exclu-
sively for the biarticular hamstrings that were in more lengthened
positions during the seated leg curl. On the other hand, both
training interventions were similarly effective in reducing sus-
ceptibility to eccentric exercise-induced muscle damage. Based
on these, the seated rather than prone leg curl is recommended
if training aims include increasing/maintaining muscle size of
the hamstrings.
This work was supported by a research grant from Mizuno Sports
Promotion Foundation (2019-5) to S. M. The authors thank the anony-
mous reviewers for their constructive comments that have substantially
improved the quality of this study.
The authors declare that there is no conflict of interest, that no com-
panies or manufacturers will benefit from the results of the study, and
that the results of the study are presented clearly, honestly, and without
fabrication, falsification, or inappropriate data manipulation. The results
of the present study do not constitute endorsement by the American
College of Sports Medicine.
REFERENCES
1. Morin JB, Gimenez P, Edouard P, et al. Sprint acceleration mechan-
ics: the major role of hamstrings in horizontal force production. Front
Physiol. 2015;6:404.
2. Guex K, Millet GP. Conceptual framework for strengthening exercises
to prevent hamstring strains. Sports Med. 2013;43(12):1207–15.
3. American College of Sports Medicine. American College of Sports
Medicine Position Stand: progression models in resistance training
for healthy adults. Med Sci Sports Exerc. 2009;41(3):687–708.
4. Garber CE, Blissmer B, Deschenes MR, et al, American College of
Sports Medicine. American College of Sports Medicine Position
Stand: quantity and quality of exercise for developing and maintain-
ing cardiorespiratory, musculoskeletal, and neuromotor fitness in ap-
parently healthy adults: guidance for prescribing exercise. Med Sci
Sports Exerc. 2011;43(7):1334–59.
5. Abe T, DeHoyos DV, Pollock ML, Garzarella L. Time course for strength
and muscle thickness changes following upper and lower body resistance
training in men and women. Eur J Appl Physiol. 2000;81(3):174–80.
6. Vissing K, Brink M, Lonbro S, et al. Muscle adaptations to plyomet-
ric vs. resistance training in untrained young men. JStrengthCond
Res. 2008;22(6):1799–810.
7. Starkey DB, Pollock ML, Ishida Y, et al. Effect of resistance training
volume on strength and muscle thickness. Med Sci Sports Exerc.
1996;28(10):1311–20.
8. Delp SL, Anderson FC, Arnold AS, et al. OpenSim: open-source
software to create and analyze dynamic simulations of movement.
IEEE Trans Biomed Eng. 2007;54(11):1940–50.
9. Arnold EM, Ward SR, Lieber RL, Delp SL. A model of the lower limb
for analysis of human movement. AnnBiomedEng. 2010;38(2):269–79.
10. Arnold EM, Delp SL. Fibre operating lengths of human lower limb
muscles during walking. Philos Trans R Soc Lond B Biol Sci. 2011;
366(1570):1530–9.
11. Alegre LM, Ferri-Morales A, Rodriguez-Casares R, Aguado X. Ef-
fects of isometric training on the knee extensor moment-angle relation-
ship and vastus lateralis muscle architecture. Eur J Appl Physiol. 2014;
114(11):2437–46.
12. Noorkoiv M, Nosaka K, Blazevich AJ. Neuromuscular adaptations
associated with knee joint angle-specific force change. Med Sci
Sports Exerc. 2014;46(8):1525–37.
13. McMahon G, Morse CI, Burden A, Winwood K, Onambele GL.
Muscular adaptations and insulin-like growth factor-1 responses to resis-
tance training are stretch-mediated. Muscle Nerve. 2014;49(1):108–19.
14. Akagi R, Hinks A, Power GA. Differential changes in muscle archi-
tecture and neuromuscular fatigability induced by isometric resis-
tance training at short and long muscle-tendon unit lengths. J Appl
Physiol (1985). 2020;129(1):173–84.
15. Kubo K, Ohgo K, Takeishi R, et al. Effects of isometric training at
different knee angles on the muscle-tendon complex in vivo. Scand
J Med Sci Sports. 2006;16(3):159–67.
16. Stasinaki AN, Zaras N, Methenitis S, et al. Triceps brachii muscle
strength and architectural adaptations with resistance training exer-
cises at short or long fascicle length. J Funct Morphol Kinesiol.
2018;3(2):28–39.
http://www.acsm-msse.org836 Official Journal of the American College of Sports Medicine
APPLIED SCIENCES
17. Schoenfeld BJ, Grgic J. Effects of range of motion on muscle devel-
opment during resistance training interventions: a systematic review.
SAGE Open Med. 2020;8:2050312120901559.
18. Maeo S, Saito A, Otsuka S, Shan X, Kanehisa H, Kawakami Y. Lo-
calization of muscle damage within the quadriceps femoris induced
by different types of eccentric exercises. Scand J Med Sci Sports.
2018;28(1):95–106.
19. Brockett CL, Morgan DL, Proske U. Predicting hamstring strain in-
jury in elite athletes. Med Sci Sports Exerc. 2004;36(3):379–87.
20. Timmins RG, Shield AJ, Williams MD, Opar DA. Is there evidence
to support the use of the angle of peak torque as a marker of hamstring
injury and re-injury risk? Sports Med. 2016;46(1):7–13.
21. Nosaka K, Newton M, Sacco P, Chapman D, Lavender A. Partial
protection against muscle damage by eccentric actions at short mus-
cle lengths. Med Sci Sports Exerc. 2005;37(5):746–53.
22. Askling CM, Tengvar M, Saartok T, Thorstensson A. Acute
first-timehamstring strains during high-speed running: a longitudinal
study including clinical and magnetic resonance imaging findings.
Am J Sports Med. 2007;35(2):197–206.
23. De Smet AA, Best TM. MR imaging of the distribution and location
of acute hamstring injuries in athletes. AJR Am J Roentgenol. 2000;
174(2):393–9.
24. Maeo S, Shan X, Otsuka S, Kanehisa H, Kawakami Y. Neuromuscu-
lar adaptations to work-matched maximal eccentric versus concentric
training. Med Sci Sports Exerc. 2018;50(8):1629–40.
25. Maeo S, Ando Y, Kanehisa H, Kawakami Y. Localization of damage
in the human leg muscles induced by downhill running. Sci Rep.
2017;7(1):5769.
26. Ho J, Tumkaya T, Aryal S, Choi H, Claridge-Chang A. Moving be-
yond Pvalues: data analysis with estimation graphics. Nat Methods.
2019;16(7):565–6.
27. Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy.
8th ed. Philadelphia: Wolters Kluwer; 2018. 1153 p.
28. Kim J, Lee J-H. A unique case of an accessory sartorius muscle. Surg
Radiol Anat. 2019;41(3):323–5.
29. Kooistra RD, de Ruiter CJ, de Haan A. Knee angle-dependent oxy-
gen consumption of human quadriceps muscles during maximal vol-
untary and electrically evoked contractions. Eur J Appl Physiol.
2008;102(2):233–42.
30. Yang H, Alnaqeeb M, Simpson H, Goldspink G. Changes in muscle
fibre type, muscle mass and IGF-I gene expression in rabbit skeletal
muscle subjected to stretch. JAnat. 1997;190(Pt 4):613–22.
31. Schoenfeld BJ. Potential mechanisms for a role of metabolic stress in
hypertrophic adaptations to resistance training. Sports Med.2013;
43(3):179–94.
32. Bourne MN, Timmins RG, Opar DA, et al. An evidence-based
framework for strengthening exercises to prevent hamstring injury.
Sports Med. 2018;48(2):251–67.
33. Ochi E, Tsuchiya Y, Nosaka K. Differences in post-exercise T2 re-
laxation time changes between eccentric and concentric contractions
of the elbow flexors. Eur J Appl Physiol. 2016;116(11–12):2145–54.
34. Bourne MN, Duhig SJ, Timmins RG, et al. Impact of the Nordic
hamstring and hip extension exercises on hamstring architecture
and morphology: implications for injury prevention. Br J Sports
Med. 2017;51(5):469–77.
35. Chen TC, Chen HL, Lin MJ, Wu CJ, Nosaka K. Muscle damage re-
sponses of the elbow flexors to four maximal eccentric exercise bouts
performed every 4 weeks. Eur J Appl Physiol. 2009;106(2):267–75.
36. Maeo S, Yamamoto M, Kanehisa H. Muscular adaptations to
short-term low-frequency downhill walking training. Int J Sports
Med. 2015;36(2):150–6.
37. Maeo S, Yamamoto M, Kanehisa H. Downhill walking training with
and without exercise-induced muscle damage similarly increase knee
extensor strength. JSportsSci. 2016;34(21):2018–26.
38. Carmona G, Mendiguchia J, Alomar X, et al. Time course and associ-
ation of functional and biochemical markers in severe semitendinosus
damage following intensive eccentric leg curls: differences between
and within subjects. Front Physiol. 2018;9:54.
39. Kubota J, Ono T, Araki M, Torii S, Okuwaki T, Fukubayashi T. Non-
uniform changes in magnetic resonance measurements of the
semitendinosus muscle following intensive eccentric exercise. Eur J
Appl Physiol. 2007;101(6):713–20.
40. Mendiguchia J, Garrues MA, Cronin JB, et al. Nonuniform changes
in MRI measurements of the thigh muscles after two hamstring
strengthening exercises. JStrengthCondRes. 2013;27(3):574–81.
41. Garrett WE Jr., Nikolaou PK, Ribbeck BM, Glisson RR, Seaber AV.
The effect of muscle architecture on the biomechanical failure prop-
erties of skeletal muscle under passive extension. Am J Sports Med.
1988;16(1):7–12.
42. Patel TJ, Das R, Friden J, Lutz GJ, Lieber RL. Sarcomere strain and
heterogeneity correlate with injury to frog skeletal muscle fiber bun-
dles. J Appl Physiol (1985). 2004;97(5):1803–13.
43. Ward SR, Eng CM, Smallwood LH, Lieber RL. Are current measure-
ments of lower extremity muscle architecture accurate? Clin Orthop
Relat Res. 2009;467(4):1074–82.
44. McHugh MP, Tyler TF. Muscle strain injury vs muscle damage: two
mutually exclusive clinical entities. Transl Sports Med. 2019;2(3):
102–8.
45. Brockett CL, Morgan DL, Proske U. Human hamstring muscles
adapt to eccentric exercise by changing optimum length. Med Sci
Sports Exerc. 2001;33(5):783–90.
46. Timmins RG, Ruddy JD, Presland J, et al. Architectural changes of
the biceps femoris long head after concentric or eccentric training.
Med Sci Sports Exerc. 2016;48(3):499–508.
47. Timmins RG, Bourne MN, Shield AJ, Williams MD, Lorenzen C,
Opar DA. Short biceps femoris fascicles and eccentric knee flexor
weakness increase the risk of hamstring injury in elite football
(soccer): a prospective cohort study. Br J Sports Med. 2016;
50(24):1524–35.
48. Franchi MV, Fitze DP, Raiteri BJ, Hahn D, Sporri J. Ultrasound-
derived biceps femoris long head fascicle length: extrapolation pit-
falls. Med Sci Sports Exerc. 2020;52(1):233–43.
49. Bolsterlee B, D’Souza A, Herbert RD. Reliability and robustness
of muscle architecture measurements obtained using diffusion
tensor imaging with anatomically constrained tractography. J Biomech.
2019;86:71–8.
50. Lichtwark GA, Farris DJ, Chen X, Hodges PW, Delp SL.
Microendoscopy reveals positive correlation in multiscale length
changes and variable sarcomere lengths across different regions of
human muscle. J Appl Physiol (1985). 2018;125(6):1812–20.
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