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Sports Biomechanics
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/rspb20
Thigh loaded wearable resistance increases
sagittal plane rotational work of the thigh
resulting in slower 50-m sprint times
Paul Macadam , John B. Cronin , Aaron M. Uthoff , Ryu Nagahara , James
Zois , Shelley Diewald , Farhan Tinwala & Jono Neville
To cite this article: Paul Macadam , John B. Cronin , Aaron M. Uthoff , Ryu Nagahara , James
Zois , Shelley Diewald , Farhan Tinwala & Jono Neville (2020): Thigh loaded wearable resistance
increases sagittal plane rotational work of the thigh resulting in slower 50-m sprint times, Sports
Biomechanics, DOI: 10.1080/14763141.2020.1762720
To link to this article: https://doi.org/10.1080/14763141.2020.1762720
Published online: 28 May 2020.
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Thigh loaded wearable resistance increases sagittal plane
rotational work of the thigh resulting in slower 50-m sprint
times
Paul Macadam
a
, John B. Cronin
a
, Aaron M. Uthoff
a
, Ryu Nagahara
b
, James Zois
c
,
Shelley Diewald
a
, Farhan Tinwala
a
and Jono Neville
a
a
Sports Performance Research Institute New Zealand (SPRINZ), AUT University, Auckland, New Zealand;
b
National Institute of Fitness and Sports in Kanoya, Kanoya, Japan;
c
Institute for Health and Sport, Victoria
University, Melbourne, Victoria, Australia
ABSTRACT
This study determined the acute changes in rotational work with thigh
attached wearable resistance (WR) of 2% body mass during 50-m
sprint-running. Fourteen athletes completed sprints with, and without,
WR in a randomised order. Sprint times were measured via timing
gates at 10-m and 50-m. Rotational kinematics were obtained over
three phases (steps 1–2, 3–6and7–10) via inertial measurement unit
attached to the left thigh. Quantification of thigh angular displacement
and peak thigh angular velocity was subsequently derived to measure
rotational work. The WR condition was found to increase sprint times
at 10-m (1.4%, effect size [ES] 0.38, p 0.06) and 50-m (1.9%, ES 0.55,
p 0.04). The WR condition resulted in trivial to small increases in
angular displacement of the thigh during all phases (0.6–3.4%, ES
0.04–0.26, p 0.09–0.91). A significant decrease in angular velocity of
the thigh was found in all step phases (−2.5% to −8.0%, ES 0.17–0.51,
p<0.001–0.04), except extension in step phase 1 with the WR.
Rotational work was increased (9.8–18.8%, ES 0.35–0.53, p < 0.001)
with WR in all phases of the sprint. Thigh attached WR provides
ameanstosignificantly increase rotational work specifictosprinting.
ARTICLE HISTORY
Received 21 January 2020
Accepted 24 April 2020
KEYWORDS
Acceleration; velocity;
kinematics; external loading
Introduction
Sprint-running is often quantified via linear measures; however, it is the product of the angular
motion of the legs and arms. It would, therefore, make sense to find training methods to
overload angular motion specific to sprinting, to maximise sprint-specific adaptations. One
such training modality is wearable resistance (WR), which involves athletes moving micro-
loads that are attached to the limbs via various methods (e.g., velcro, bands, inserted into
sleeves) (Macadam, Cronin et al., 2017). There has been a re-emergence of the use of this
technology, especially with regards to sprint research, however, one of the challenges asso-
ciated with WR limb loading is quantifying the workload given the angular overload it
provides (Macadam et al., 2018). The addition of WR to a limb such as the thigh, is thought
to increase the rotational inertia and therefore the turning forces/torques required to move
this additional load (Martin & Cavanagh, 1990;Myers&Steudel,1985), and hence it is
CONTACT Paul Macadam paul.macadam@aut.ac.nz
SPORTS BIOMECHANICS
https://doi.org/10.1080/14763141.2020.1762720
© 2020 Informa UK Limited, trading as Taylor & Francis Group
thought rotational work at the hip would be increased. However, it may be that there is
a concomitant decrease in angular displacement with such loading, and hence workload does
not in fact increase but rather stays the same or decreases. Therefore, of interest to the authors
is understanding the effects of WR on angular work of the thigh during sprinting.
Three studies have assessed the acute rotational work effects of WR attached to the thigh
during treadmill running at speeds of 2.68–3.3 m/s. Thigh loads of 0.6% and 1.4% body
mass (BM) were used in two studies (Martin, 1985; Martin & Cavanagh, 1990), while Myers
and Steudel (1985) used WR totalling 4.8–5.8% BM. The positioning of the WR ranged
from proximal from the hip to mid-thigh in these previous studies. Mechanical workload
was significantly increased (9.5%) with 1.4% BM WR but did not significantly differ from
unloaded running (2.5%) with the lighter WR of 0.6% BM (Martin, 1985). Though thigh
loading increased the moment of inertia by 2%, no significant changes in work values were
reported (Martin & Cavanagh, 1990). The greater loading of 4.8–5.8% BM significantly
increased the entire limb’s moment of inertia by 1%, and was reported to have increased
mechanical work, however, the authors did not quantify these changes (Myers & Steudel,
1985). As can be observed there are no systematic trends in the results related to the effect of
thigh worn WR on rotational mechanical workload. This can be attributed in part to: 1)
magnitude of loads (0.6% to 5.8% BM); 2) placement of loads (proximal to mid-femur)
which effects rotational inertia; 3) the different methodologies used (workload calcula-
tions); and, 4) the duration and speeds of the running phase investigated.
The previous thigh WR running studies (Martin, 1985; Martin & Cavanagh, 1990;
Myers & Steudel, 1985) collected rotational kinematics from standard definition video.
However, recent developments in technology have enabled rotational kinematics to be
collected from a wearable inertial measurement unit (IMU), which enable a greater
volume of capture data to be collected outside of a laboratory setting, providing a more
ecologically valid method for data collection. Thigh attached IMUs were previously used
to collect rotational kinematics of the thigh during running (Nüesch et al., 2017) and
sprinting (Schmidt, Rheinländer, Wille et al., 2016a; Schmidt et al., 2016b). Previous IMU
sprint studies have found that rotational kinematics measures were valid with root-mean
-square error measures in shank angular displacement (≤5%) and velocity (≤10%), and
trunk angular displacement (≤5%) (Bergamini et al., 2013; Channells et al., 2005), and
can be used to reliably report trunk angular displacement (≤6%) (Bergamini et al., 2013).
Though acute rotational work effects from WR have been assessed at submaximal running
speeds (Martin, 1985; Martin & Cavanagh, 1990;Myers&Steudel,1985), WR thigh loading
has yet to be investigated at maximal effort sprint-running speeds. Moreover, from prior
sprint studies, leg attached WR has been found to increase horizontal force (5-6%) during
short distance sprints suggesting it may be a beneficial form of improving a key determinant
of accelerated sprinting (Macadam et al., 2018). No studies to date have quantified mechan-
ical workload with WR thigh loads at speeds greater than 3.3 m/s. As intimated previously, it
is important to understand whether such loading actually provides a mechanical overload of
sprint-specific musculature, as the determinants of rotational work (rotational inertia, accel-
eration and displacement), may be affected in a manner where the network from thigh
loading is in-substantial, i.e., increases in rotational inertia may be negated by a counteracting
influence of decreased angular displacement or velocity. Therefore, of interest to the authors
is understanding the effects of WR using IMU technology, on angular work of the thigh
during sprinting. It was hypothesised that the effects of rotational inertia (I = mr
2
)wouldbe
2P. MACADAM ET AL.
greater than any decrease in angular acceleration and displacement, hence WR would provide
asprint-specific increase in the mechanical workload of the thigh musculature.
Methods
Participants
Fifteen male athletes from university athletic clubs (21.0 ± 2.5 years; 174.0 ± 4.1 cm;
67.5 ± 5.4 kg; 9.2 ± 2.5 training years; 11.3 ± 0.5 s 100 m personal best time) volunteered to
participate in the study. Written informed consent was obtained from the participants prior to
their participation and they were advised that they could withdraw from the study at any time
without repercussion. The Institutional Ethics Committee of Auckland University of
Technology provided approval for this study.
Procedures and data processing
Participants performed four trials of a 50-m sprint from a block start, comprised of two
repetitions under each condition: 1) WR 2% BM; and 2) unloaded (i.e., UL = 0% BM).
Participants were requested to sprint through the 50-m mark in order to ensure no decelera-
tion throughout the distance. The order of the conditions was randomised with a random
number generator. Each trial was separated by 10 min of passive rest (Macadam et al., 2019).
Participants wore Lila
TM
Exogen
TM
compression shorts (Sportboleh Sdh Bhd, Malaysia)
for the duration of the testing session. The Exogen
TM
exoskeleton shorts enabled loads
(with Velcro backing) of 0.05–0.2 kg to be attached. Prior running WR thigh studies placed
the loads mid-thigh to proximal (Martin, 1985; Myers & Steudel, 1985). Given there would
be greater inertial property changes of the limb with a more distal loading, WR totalling 2%
BM was attached to the distal aspect of each thigh to increase the moment of inertia from
the hip. Therefore, 1% BM was placed evenly around each thigh with 2/3 of the load
attached predominately anterior and the remaining 1/3 posterior (Figure 1).
The 10-m and 50-m sprint times were measured using a photocell system (TC Timing
System; Brower Timing Systems, Draper, UT, USA). Photocell units were set at the 10-m and
50-m mark, which were initiated by an electric starting gun (Digi Pistol, Molten, Hiroshima,
Japan).
AnIMU(IMeasureULimited,Auckland,New Zealand) consisting of a ± 16 g 3-axis
accelerometer, ±2000°/s 3-axis gyroscope, and a ± 1200µT 3-axis magnetometer was used to
collect sagittal plane rotational kinematics from the left thigh. Data were logged to the
onboard memory of the IMU at 500 Hz for the duration of the trials, and then downloaded
after each session for processing. The accelerometer was calibrated using gravity vectors
recorded in each of the primary orientations, and the gyroscope was factory calibrated. The
IMU was attached to the middle and lateral surface of the thigh, corresponding to the mid-
point between the greater trochanter and lateral epicondyle of the femur, using elastic straps
with the tape placed onto the strap and leg to minimise skin and clothing artefact.
Acceleration and rotational velocity data were imported into MATLAB (V2019b,
Mathworks, Natick, Massachusetts, USA). Orientation of the sensors were calculated using
acomplimentaryfiler (Matlab 2019b). The sensor-fusion algorithm was chosen to minimise
the effects of gyroscope drift and accelerometer noise. The recorded waveforms from the
SPORTS BIOMECHANICS 3
IMU for kinematics of the thigh were separated by steps by identifying the maximum flexion
and extension (thigh range of motion) in the Z-axis, corresponding to the sagittal plane. Only
a local reference frame was needed for the analysis, therefore the magnetometer data were not
utilised. Cross-over movement from other planes was assumed to be minimal.
Data analysis
As the smallest number of steps collected from the left leg among the participants was 10
during the 50-m sprint, therefore the maximum step number used for analysis was
standardised to 10. To understand how conditions affected different phases of the sprint,
the analysis was completed from breakpoint transitions, identified as step acceleration
phases 1:1–2 steps, 2:3–6 steps, 3:7–10 steps. This analysis was similar to the bilateral
analysis used by Nagahara et al. (2014), Nagahara et al. (2018), and Von Lieres und
Wilkau et al. (2018). An average of all 10 left steps was also compared between conditions
to reflect the cumulative work. Due to the specific muscular and technical demands
represented during the block-clearing phase of sprinting (Debaere et al., 2012) this phase
was not included for analysis, and analyses were performed from the first step onwards.
Using orientation data obtained from the IMU, rotational work was determined by
quantifying the changes in sagittal plane rotational kinetic energy. The dominant accelera-
tion movement when wearing a hip attached sensor was in the flexion-extension direction,
and movement in this plane represents the best single-axis indicator for predicting energy
expenditure (Vathsangam et al., 2011). This rotational work method is similar to previous
studies (Martin & Cavanagh, 1990; Myers & Steudel, 1985)asfollows:
rotational energy ¼1
=
2Iω2
where rotational energy (J/s = kgm
2
/s), I = moment of inertia (kgm
2
), and ω= angular
velocity of the segment (radians/s). This J/s describes the amount of action occurring
through the summation of energy over time.
Figure 1. Wearable resistance totalling 2% BM (i.e. 1% body mass per leg) attached distally to the
thigh.
4P. MACADAM ET AL.
Moment of inertia for the thigh mass and length was obtained from mathematical
modelling approach from Japanese male athletes (Ae et al., 1992). The value of the
moment of inertia was obtained from the following formula:
I¼mk2
where m = total segment mass, k = distance of the radius of gyration. The radius of
gyration represents the object’s mass distribution with respect to a given axis of rotation.
It is the distance from the axis of rotation to a point at which the mass of the body can
theoretically be concentrated without altering the inertial characteristics of the rotating
body. Due to the specific short lengths, the WR was placed at the end of the shorts,
equivalent to approximately 80% distal from the hip joint centre as shown by the dashed
line in Figure 2.
0
0.1
0.2
0.3
0.4
0.5
Figure 2. Example from a thigh of 0.5 m length and 7 kg mass. Dashed line shows wearable resistance
placement.
SPORTS BIOMECHANICS 5
Example calculation of moment of inertia for unloaded and WR conditions from 70 kg
participant with 0.5 m thigh length, therefore 700 g was added as WR:
Unloaded I ¼2:0kgðÞ0:1mðÞ
2þ2:0kgðÞ0:2mðÞ
2þ1:5kgðÞ0:3mðÞ
2
þ1:5kg
ðÞ
0:4m
ðÞ
2þ1:0kg
ðÞ
0:5m
ðÞ
2
Wearable resistance I ¼2:0kgðÞ0:1mðÞ
2þ2:0kgðÞ0:2mðÞ
2þ1:5kgðÞ0:3mðÞ
2
þ2:2kgðÞ0:4mðÞ
2þ1:0kgðÞ0:5mðÞ
2
Statistical analysis
Standard descriptive statistics (means and standard deviations) were reported for all
statistical comparisons. The average data from the two repetitions under each condition
were used for analysis. The Shapiro-Wilk statistic was used to check the data for normal
distribution. Effect size statistics (reported using Cohen’s d) and 90% confidence intervals
(CI) determined the magnitude of differences between the two conditions with values
reported as trivial (<0.2), small (0.21–0.5), moderate (0.51–0.79) or large (>0.8) (Cohen,
1988). ES was calculated by the mean difference between groups, dividing the result by
the pooled standard deviation, and were used to quantify the size of the difference
between two groups (Cohen, 1988). Statistical differences in variables of interest across
WR and unloaded conditions were determined using a paired t-test. Statistical signifi-
cance was set at an alpha level of p < 0.05.
Test–retest reliability of the cumulative rotational kinematics were assessed from two trials
with each condition using the coefficient of variation (CV) and intraclass correlation coeffi-
cient (ICC) with 90% CI calculated for each variable. The CV was calculated from (Standard
Deviation/Mean) *100. The current investigation set reliability thresholds of CV ≤10%
(Atkinson & Nevill, 1998), ICC ≥0.70 (Meylan et al., 2012).
Results
The CVs (<9%) and ICCs (>0.92) were found to be reliable for both conditions and for all
variables measured (Table 1).
Sprint times were increased with the WR condition at 10 m (1.4%, ES = 0.38,
p = 0.063) and significantly at 50 m (1.9%, ES = 0.55, p = 0.044) compared to the
unloaded condition (Table 2).
No significant differences in angular displacement of the thigh occurred during
any step phases with trivial to small ES increases (0.6–3.4%, ES = 0.04–0.26) reported
(Figure 3). Regarding angular velocity of the thigh, no significant changes were found
in the extension movement (0.9%, ES = 0.04, p = 0.743) in step phase 1, however,
flexion was significantly decreased (−8.0%, ES = 0.48, p = 0.011) with WR during this
phase (Figure 4). During step phase 2, extension (−3.6%, ES = 0.33, p = <0.001) and
flexion (−5.5% ES = 0.51, p = <0.001) angular velocities were decreased with WR.
Similarly, WR resulted in decreased extension (−2.3%, ES = 0.26, p = 0.039) and
flexion (−4.6%, ES = 0.46, p = <0.001) angular velocities during step phase 3, and
6P. MACADAM ET AL.
cumulatively (extension −2.5%, ES = 0.17, p = 0.003, flexion −5.6%, ES = 0.44,
p = <0.001).
Inertia of the thigh with WR (0.494 kgm
2
/s) was found to be significantly increased by
14.8% (ES 0.66, p = <0.001) compared to the unloaded thigh (0.421 kgm
2
/s). Rotational
energy was significantly increased during all phases of the sprint (9.8–18.8%,
ES = 0.09–0.55, p = <0.001) compared to the unloaded sprint condition (Figure 5).
Table 1. Test–retest reliability based on the coefficient of variation (CV) and intraclass correlation (ICC)
with 90% confidence intervals (CI) for rotational kinematics.
Unloaded Wearable resistance
Variables CV (%) ICC (90% CI) CV (%) ICC (90% CI)
Flexion angular displacement 6.6 0.94 (0.89–0.98) 7.0 0.93 (0.88–0.98)
Extension angular displacement 6.0 0.96 (0.91–0.98) 6.3 0.94 (0.89–0.97)
Flexion angular velocity 8.8 0.95 (0.91–0.99) 9.0 0.92 (0.87–0.98)
Extension angular velocity 8.5 0.95 (0.87–0.98) 8.8 0.94 (0.86–0.97)
Table 2. Sprint times (s) changes for unloaded and wearable resistance sprint-running.
Mean ± SD.
Sprint distance Unloaded Wearable resistance Effect size (90% CI)
10 m (s) 2.15 ± 0.07 2.18 ± 0.08 0.38 (−0.36: 1.09)
50 m (s) 6.64 ± 0.23 6.78 ± 0.25
a
0.55 (−0.19: 1.32)
a
Significant difference from unloaded condition. CI = confidence interval
0
20
40
60
80
100
120
Unloaded Wearable resistance
Ext Flex Ext Flex Ext Flex Ext Flex
Ste
p
Phase 1 Ste
p
Phase 2 Ste
p
Phase 3 Avera
g
e
)°(tnemecalpsiDralugnA
Figure 3. Angular displacement (°) changes of the thigh for unloaded and wearable resistance sprint-
running. Mean ± SD.
SPORTS BIOMECHANICS 7
Discussion and implication
This study aimed to determine the acute changes, measured from an IMU, on rotational
kinematics and sprint performance when WR of 2% BM was attached to thighs during
overground maximal sprint-running. The main findings were that sprint-running with
0
100
200
300
400
500
600
700
800
900
1000
Unloaded Wearable resistance
Angular Velocity (°/s)
Ext Flex Ext Flex Ext Flex Ext Flex
Step Phase 1 Step Phase 2 Step Phase 3 Average
*
*
*
*
*
*
*
Figure 4. Angular velocity (°/s) changes of the thigh for unloaded and wearable resistance sprint-
running. Mean ± SD.
0
50
100
150
200
250
300
350
Unloaded Wearable resistance
*
*
*
*
*
*
Rotational energy (J/s)
Ext Flex Ext Flex Ext Flex Ext Flex
Step Phase 1 Step Phase 2 Step Phase 3 Average
*
*
Figure 5. Rotational energy(J/s) changes of the thigh for unloaded and wearable resistance sprint-
running. Mean ± SD.
8P. MACADAM ET AL.
WR attached to the thighs resulted in: 1) increased sprint times at 10 m (1.4%, ES = 0.38)
and significantly increased 50-m times (1.9%, ES = 0.55); 2) increased angular displace-
ment (0.6–3.4%, ES = 0.04–0.26), and significantly decreased angular velocity (−2.5% to
−8.0%, ES = 0.17–0.51), with greater changes in flexion (ES = 0.44–0.51) than extension
(ES 0.04–0.33) movements; and, 3) significantly greater rotational work during all phases
of the sprint (9.8–18.8%, ES = 0.35–0.53). These results support the hypothesis that
loading the thighs using WR would affect angular displacement and angular velocity of
the thigh, however, the effects of the moment of inertia were greater than these reduc-
tions, resulting in increased rotational work of the hip musculature. Therefore, it appears
that WR significantly overloads thigh rotational movements, resulting in a sprint-specific
overload as evidenced by increased 50-m times.
The findings regarding sprint times from this study are comparable to previous studies
with whole leg WR (2.4-5% BM) which found no significant changes in sprint times at
10 m, however, beyond 10-m significantly increased sprint times were reported (Bennett
et al., 2009; Macadam, Simperingham et al., 2017; Simperingham & Cronin, 2014).
Beyond the initial take-offsteps and the early acceleration phase, the body is in a more
upright position, therefore, with WR attached distally to the thighs, athletes would have
been required to overcome a greater amount of rotational inertia, and hence work.
Therefore, it appears that as a consequence of the increase in the rotational work of the
thighs, sprint performance is more affected by the addition of WR as the sprint distance
increases. Given the work–energy relationship, this makes sense, as the velocity of
movement affects angular kinetic energy and therefore mechanical work, i.e., the kine-
matic and kinetic effects of WR increase with a velocity of movement.
Changes to angular displacement were trivial to small. Therefore, it seems that the
range of motion is similar between unloaded and thigh worn WR, the increased rota-
tional inertia minimally affecting angular displacement. Given these changes, or lack of,
and in conjunction with other studies that have reported non-significant changes to step
length with leg WR (Macadam, Simperingham et al., 2017; Simperingham & Cronin,
2014), it appears that thigh WR results in minimal effects to angular displacement and
therefore step length.
Interestingly, the time to move through these ranges of motion is slower, the increased
rotational inertia having a significantly greater influence on angular velocity in all phases
of the sprint (~5-8%). Though both flexion and extension actions were significantly
decreased in all step phases (except extension in step phase 1), it seems the rotational
inertia was more influential during hip flexion. Therefore, it could be proposed that WR
may be a means for overloading and subsequently strengthening hip flexors rather than
hip extensors. The greater overload changes between movements would seem logical as
the flexor motion is an anti-gravity action and any additional thigh loading will need to
be moved against gravity, whereas the extension moments are not impacted as much by
gravity. Loading the thigh most likely influenced the acceleration—deceleration—re-
acceleration of the thigh for each step, which in turn affects the angular velocity of the
limbs and therefore slower step frequencies result, i.e., slower swing phase velocity, which
compromises step frequency. These findings align with other sprint studies where step
frequency significantly decreased with leg loaded WR (Macadam, Simperingham et al.,
2017; Simperingham & Cronin, 2014).
SPORTS BIOMECHANICS 9
Royer and Martin (2005) previously noted that adding load to a limb increased its
mass and moment of inertia. This was certainly the case with distal attached thigh WR in
the current study resulting in a significantly increased moment of inertia of the thigh by
~14% compared to an unloaded thigh. From the previous running WR studies (Martin &
Cavanagh, 1990; Myers & Steudel, 1985), the moment of inertia for the entire leg
increased by 1% with ~5% BM and by 2% with 0.6% BM, highlighting differences in
methodologies between the studies, particular related to the distance of the WR in
relation to the hip joint axis in the sagittal place. Moreover, as the prior studies were
completed at treadmill running speeds and used a more proximal placement compared to
the more distal placed WR in this study, greater inertia changes would be expected as the
load is placed further from the hip joint and faster running speeds were achieved.
Consequently, the effects on rotational work were significantly greater (10–18.3%,
ES = 0.09–0.55) throughout all phases of the sprint.
Findings from this study relate to the rotational work calculation being based on the
joint and segment approach of the thigh, however, this method does not measure work
done elsewhere, such as passive wobbling of viscera, or the motion of unmeasured joints/
segments (e.g., trunk and arms). Assuming rigid-body segments, peripheral work
changes reflect body movements relative to the centre of mass, though this estimate
fails to capture energy changes due to non-rigid-body motion relative to each individual
body segment’s centre of mass (e.g., deformation of the thigh segment that does not
contribute to the motion of the thigh’s centre of mass). Linear kinetic and potential
energy are not accounted for with this analysis. Moreover, only one plane of movement
was analysed, though there will still be some movement in other planes that is not being
accounted for, it was assumed to be minimal.
Conclusion
WR of 2% BM results in the musculature of the hip having to work harder to maintain
angular displacement and velocity, whilst trying to sustain linear speed. Angular
displacement and therefore step length are less affected by rotational inertia, and
angular velocity and therefore step frequency are more affected. It also appears WR
produces a greater flexor overload, though extensors are still significantly overloaded.
Rotational kinematic findings add to the previous step kinematic studies and enable
further understanding of how WR affects sprint performance. Moreover, the results
with 2% BM WR aid in adding to the load spectrum analysis from prior sprint WR
studies.
Sprinting with thigh WR provides a specific sprint training tool to significantly over-
load the rotational work experienced at the thighs, therefore, this form of loaded
sprinting is essentially a resistance training exercise performed at high velocity, the
resisted motion highly specific to sprint running. Beyond the initial take-offsteps and
early acceleration phase, the cumulative effect of thigh WR is that athletes are required to
produce a greater amount of rotational work to overcome the additional inertia of the
thigh, which in turn leads to increased sprint times. With repeated and systematic use of
WR it is expected that athletes will adapt to the overload and the rotational musculature
of the hip become stronger specific to the mechanics of sprinting. Future studies,
however, are required to assess long-term adaption to changes in rotational kinematics
10 P. MACADAM ET AL.
and sprint-performance with this form of sprint-specific loading.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
Paul Macadam received funding from Sportboleh Sdh Bhd, Malaysia.
ORCID
Paul Macadam http://orcid.org/0000-0002-2077-5386
Aaron M. Uthoffhttp://orcid.org/0000-0002-6737-0562
Ryu Nagahara http://orcid.org/0000-0001-9101-9759
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