tibialis anterior, extensor digitorum longus, and extensor hal-
lucis longus. The lateral shank compartment included the
peroneus longus and brevis. The deep posterior compartment
consisted of plantaris, tibialis posterior,ﬂexor digitorum lon-
gus, and ﬂexor hallucis longus. All muscles were manually
segmented in every other image (i.e., every 20 mm) starting
from the most proximal image in which the muscle appeared,
except the tensor fasciae latae, gluteus medius and minimus
(combined), and popliteus, which were manually segmented
in every slice (i.e., every 10 mm) due to their short length. The
volume of each individual muscle (Vm) was calculated using
previously outlined methods (16)a sf o l l o w s :
Vm ¼
Xn/C0 1
i¼1
h
2 ðAmi þ Ami þ 1Þ
where Am represents the muscle CSA calculated from each
image, i is the image number, n is the total number of
images, andh is the distance between images. The volume of
ﬁve functional muscle groups was calculated as the sum
of the following muscles: hip extensors (gluteus maxi-
mus, adductor magnus, BFlh, SM, and ST), hip ﬂexors
(iliopsoas, RF, sartorius, and tensor fasciae latae), knee
extensors (RF, VI, VM, and VL), kneeﬂexors (gracilis,
BFlh and BFsh, SM, ST, sartorius, popliteus, and medial
and lateral gastrocnemius), and plantar ﬂexors (medial
and lateral gastrocnemius and soleus). The sum of all the
measured lower-body muscles was also quantiﬁed as the
volume of“all muscles.”
Once muscle MRI scanning had been completed, aﬂex
coil (GE Medical) was used to acquire unilateral T1-weighted
axial (time of repetition/time to echo 650/9.476 ms, image
matrix 512 /C2 512, ﬁeld of view 180/C2 180 mm, pixel size
0.3516 /C2 0.3516 mm, slice thickness 2 mm, and interslice gap
0 mm) and sagittal images (time of repetition/time to echo
606/9.512 ms, image matrix 512/C2 512, ﬁeld of view 180/C2 180
mm, pixel size 0.3516/C2 0.3516 mm, slice thickness 2 mm,
and interslice gap¼ 0 mm) from both knee joints. The axial
images were obtained perpendicular to the line of the tendon
from/C24 2 cm superior to the apex of the patella to/C24 2c m
inferior to the patellar tendon’s inferior insertion. Patellar
tendon CSA was measured in each contiguous image along
the length of the tendon (i.e., from theﬁrst image where the
patella was no longer visible to theﬁnal image before the tib-
ial insertion). The axial images of the patellar tendon were
viewed in grayscale, sharpened, and the perimeter manually
outlined. The average of all measured axial patellar tendon
CSAs was calculated to produce a mean tendon CSA (mm2)
for each leg. The moment arm length of the patellar tendon
for each leg was estimated from sagittal plane images as the
perpendicular distance from the patellar tendon to the mid-
point of tibiofemoral contact (17).
Countermovement Jump
Following an /C24 10-min self-selected whole body loaded
barbell-based warm-up and three submaximum warm-up
CMJs performed with/C24 50% of perceived maximum effort,
the WSM performed three maximal effort CMJs, with 30 s of
rest between jumps, on a portable Kistler force plate (Quattro
Jump, Type 9290AD, Kistler, Switzerland), interfaced with a
personal computer. Prior to all jumps, the participant was
instructed to stand still on the force plate in an upright pos-
ture with their arms by their sides. Sampling was initiated
when they provided an indication they were ready to begin,
and after a 2-s pause to collect the force due to body mass
and a 3-s countdown, the participant performed a CMJ for
maximal height, with arm movement and the depth of coun-
termovement self-selected by the participant. The Quattro
jump device records vertical ground reaction force at a sam-
pling frequency of 500 Hz and calculates jump height and
peak power using integration/double integration of the force
signal (Quattro jump software, type 2822A1-1, version 1.1.1.4)
to derive velocity (multiplied by force to calculate power)
and displacement (jump height).
Isometric Midthigh Pull