Influence of Resisted Sled-Pull Training on the Sprint Force-Velocity Profile of Male High- School Athletes

Abstract

Cahill, MJ, Oliver, JL, Cronin, JB, Clark, K, Cross, MR, Lloyd, RS, and Lee, JE. Influence of resisted sled-pull training on the sprint force-velocity profile of male high-school athletes. J Strength Cond Res XX(X): 000-000, 2020-Although resisted sled towing is a commonly used method of sprint-specific training, little uniformity exists around training guidelines for practitioners. The aim of this study was to assess the effectiveness of unresisted and resisted sled-pull training across multiple loads. Fifty-three male high-school athletes were assigned to an unresisted (n 5 12) or 1 of 3 resisted groups: light (n 5 15), moderate (n 5 14), and heavy (n 5 12) corresponding to loads of 44 6 4 %BM, 89 6 8 %BM, and 133 6 12 %BM that caused a 25, 50, and 75% velocity decrement in maximum sprint speed, respectively. All subjects performed 2 sled-pull training sessions twice weekly for 8 weeks. Split times of 5, 10, and 20 m improved across all resisted groups (d 5 0.40-1.04, p , 0.01) but did not improve with unresisted sprinting. However, the magnitude of the gains increased most within the heavy group, with the greatest improvement observed over the first 10 m (d $ 1.04). Changes in preintervention to postintervention force-velocity profiles were specific to the loading prescribed during training. Specifically, F 0 increased most in moderate to heavy groups (d 5 1.08-1.19); Vmax significantly decreased in the heavy group but increased in the unresisted group (d 5 012-0.44); whereas, Pmax increased across all resisted groups (d 5 0.39-1.03). The results of this study suggest that the greatest gains in short distance sprint performance, especially initial acceleration, are achieved using much heavier sled loads than previously studied in young athletes.

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Original Research
Influence of Resisted Sled-Pull Training on the
Sprint Force-Velocity Profile of Male High-
School Athletes
Miche ´al J. Cahill,
1,2
Jon L. Oliver,
2,3
John B. Cronin,
2
Kenneth Clark,
4
Matt R. Cross,
2,5
Rhodri S. Lloyd,
2,3,6
and
Jeong E. Lee
7
1
Applied Health and Performance Department, Athlete Training and Health, Allen, Texas
2
Sports Performance Research Institute New
Zealand, Auckland University of Technology, Auckland, New Zealand;
3
Youth Physical Development Center, Cardiff Metropolitan
University, Cardiff, United Kingdoms;
4
Department of Kinesiology, West Chester University, West Chester, Pennsylvania;
5
Interuniversity Laboratory of Motricity Biology, University Savoie Mont Blanc, Chamb ´ery, France;
6
Center for Sport Science and
Human Performance, Waikato Institute of Technology, Hamilton, New Zealand; and
7
Department of Statistics, University of Auckland,
Auckland, New Zealand
Abstract
Cahill, MJ, Oliver, JL, Cronin, JB, Clark, K, Cross, MR, Lloyd, RS, and Lee, JE. Influence of resisted sled-pull training on the sprint
force-velocity profile of male high-school athletes. J Strength Cond Res XX(X): 000–000, 2020—Although resisted sled towing is a
commonly used method of sprint-specific training, little uniformity exists around training guidelines for practitioners. The aim of this
study was to assess the effectiveness of unresisted and resisted sled-pull training across multiple loads. Fifty-three male high-
school athletes were assigned to an unresisted (n512) or 1 of 3 resisted groups: light (n515), moderate (n514), and heavy (n5
12) corresponding to loads of 44 64 %BM, 89 68 %BM, and 133 612 %BM that caused a 25, 50, and 75% velocity decrement in
maximum sprint speed, respectively. All subjects performed 2 sled-pull training sessions twice weekly for 8 weeks. Split times of 5,
10, and 20 m improved across all resisted groups (d50.40–1.04, p,0.01) but did not improve with unresisted sprinting. However,
the magnitude of the gains increased most within the heavy group, with the greatest improvement observed over the first 10 m (d $
1.04). Changes in preintervention to postintervention force-velocity profiles were specific to the loading prescribed during training.
Specifically, F
0
increased most in moderate to heavy groups (d 51.08–1.19); Vmax significantly decreased in the heavy group but
increased in the unresisted group (d5012–0.44); whereas, Pmax increased across all resisted groups (d50.39–1.03). The results
of this study suggest that the greatest gains in short distance sprint performance, especially initial acceleration, are achieved using
much heavier sled loads than previously studied in young athletes.
Key Words: horizontal strength training, resisted sprinting, acceleration, youth
Introduction
The development of sprint speed during childhood is a critical
factor for success in young athletes (10). Natural increases in
speed have been shown to be nonlinear in youth populations, with
a preadolescent and postadolescent spurt due to rapid de-
velopment of the central nervous system and increase in hormone
levels at the onset of puberty, respectively (19,24). Postpeak
height velocity (PHV) improvements in speed tend to diminish
because of physical maturation, and increases in speed are largely
dependent on adaptation to the training methods and stimuli the
youth athlete experiences (19). Researchers have examined both
specific and nonspecific methods of enhancing sprint perfor-
mance in young athletes (14,21,30). Nonspecific methods of
improving sprint performance primarily include resistance
training, plyometric training, or a combination of both, with
varied responses observed across different stages of maturation
(16). Specific training includes modes of training that more closely
reflect the demands and movement patterns of sprinting, such as
free, assisted, and resisted sprinting (4,6,26). Supporting the
concept of training specificity, sprint-specific methods of training
have been shown to improve sprint performance in young athletes
to a greater extent than nonsprint specific methods (30).
Resisted sled pulling is a commonly researched form of resisted
sprinting (3,26). Until recently, researchers commonly recommended
an external loading that caused no greater than a 10% decrement in
maximum sprint velocity, or a load of #12.6 percent body mass (%
BM) aimed at minimizing disruption to sprint mechanics (1,17).
More recently, researchers have examined the acute influence of load
during resisted sled training on sprint kinetics with loads ranging
from light to heavy, to target specific force and velocity training
zones during horizontal work (4,12). The orientation of the force
application in a horizontal direction has also been shown to increase
with load during sled pulling (25). In a recent systematic review of
resisted sled-pull training studies, Petrakos et al. (26) surmised that
heavy sled-pull training will improve the initial acceleration phase of
a sprint. Positive adaptation to acceleration or maximal velocity is a
function of sled load because of production of high horizontal forces
at low velocities or vice versa. Recent empirical research supports this
suggestion, with soccer players training with a heavy sled load sig-
nificantly improving acceleration and horizontal force beyond that
of a group of players training with unresisted sprints (23). No re-
search has yet investigated training across multiple loads and
Address co rrespondence to Miche ´al J. Cahill, mcahill@athleteth.com.
Journal of Strength and Conditioning Research 00(00)/1–9
ª2020 National Strength and Conditioning Association
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intensities to determine the effect on an athlete’s force velocity profile
during sled pulling.
A previous limitation of sled-pull training is the use of
loading based solely on a set percentage of body mass (%BM)
for all individuals because friction, strength, training history,
and maturation are all likely to influence the relative ability to
tolerate external loads (3,29). An alternative method for
loading a sled involves providing subjects with a load that
causes a given reduction in maximal velocity when compared
with unresisted sprinting (Vdec) (7,27). Using this method, the
highly linear relationships between force-velocity and load-
velocity during sled pulling has allowed researchers to de-
termine the optimal sled load (Lopt) to maximize power pro-
duction (3,7). Lopt is defined as the load that causes a
reduction in maximum sprint velocity by 50% and therefore
optimizes power production because of the parabolic re-
lationship between power and velocity (7). Highlighting the
need to prescribe individual sled pulling loads, Cahill et al. (5)
recently showed that across a large group of youth athletes
Lopt ranged from 71 to 107 %BM. Such an approach of pre-
scriptionby%BMwouldleadtosignificantvariationinde-
sired training zones potentially leading to an inefficient and
inconsistent stimulus being applied throughout training. Al-
though Lopt targets maximizing power (Pmax) production
during sprinting, this generalized approach of training using
Lopt may not be the most effective in all athletes because of
individual characteristics. Cross et al. (8) reported varied re-
sponses across individuals after resisted sprint training at Lopt,
speculating that this was due to individual variability in pre-
training force-velocity profiles. Sled loads that reduce sprint
velocity by 25 and 75% have recently been suggested to rep-
resent light and heavy loads that target speed-strength and
strength-speed qualities of the force-velocity relationship (3).
Increases in sprinting performance may be manipulated
through a targeted load within a given zone of training to
improve initial acceleration, transitional/late acceleration, or
maximum velocity. Whether that is the case is unknown, more
studies are needed to determine to determine if lighter or
heavier loads are required to provide more consistent gains in
speed and targeted adaptations within sprinting performance
across subjects.
In the limited research available on resisted sled pulling in young
athletes, maturation differences have been shown to influence ad-
aptation to sled pulling both acutely and longitudinally (28,29).
Immature athletes were found to be slowed by 50% more than
mature athletes when working against a load set as a %BM (29).
Post-PHV athletes have also been shown to respond better to
resisted sled pulling than pre-PHV athletes over the course of a 6-
week intervention (28). Most resistance training studies in youth
have been conducted using more traditional compound exercises in
a vertical plane of motion. Subsequently, a meta-analysis con-
cluded that resistance training at heavier loads produced greater
gains in strength, speed, and power (14) in young athletes, which
may reflect the considerable potential of youth athletes to improve
force production (13,32). If sled pulling is considered as a spe-
cialized form of resistance training, then it may be speculated that
high-school athletes will benefit particularly well from sled-pull
training with heavy loads, but research is needed to confirm this.
There is currently a paucity of research that has directly
compared responses with sled-pull training at a range of loads
from across the force-velocity spectrum and very little research
with young athletes. Therefore, the aim of this study was to
assess the effectiveness of unresisted and resisted sled-pull
training over an 8-week period at light, moderate, and heavy
loads in high-school athletes.
Methods
Experimental Approach to the Problem
To determine the effectiveness of resisted sled pulling across a range
of loads corresponding to different training zones, 53 male high-
school athletes undertook an 8-week, twice weekly, training in-
tervention. Pretesting assessed each athlete’s load-velocity profile
across unresisted anda number of resisted sprints and thensubjects
were matched for 20-m sprint times and randomly divided into 4
groups of athletes who trained with either no load, or light, mod-
erate, or heavy sled loads. Those loads corresponded to a resistance
that reduced velocity by 25, 50, and 75%, respectively. Pre-
intervention and postintervention assessments included jump and
sprint testing, with step kinematic and force-velocity profiles cal-
culated during the latter. This study was approved by the in-
stitutional review board of West Chester University.
Subjects
Fifty-three male high-school athletes (mean 6SD: 16.9 60.8
years; height, 1.75 67.1 cm; body mass, 76.4 613.6 kg; and
maximum velocity (V
max
); 8.29 60.51 m·s
21
PHV; 1.5 60.7
years) from 2 sports (rugby and lacrosse) were recruited to par-
ticipate in this study during their off-season. All subjects’bi-
ological maturity was established as post-PHV using a
noninvasive method of calculating the age at PHV according to
Mirwald et al. (20). All subjects had a minimum of 1-year re-
sistance training experience, although athletes were familiar with
resisted sprinting, they had never performed a cumulative struc-
tured block of resisted sprint training. All subjects were healthy
and free from injury at the time of testing. Written informed
consent was obtained from a parent/guardian and assent from
each subject before participation. Experimental procedures were
approved by an institutional ethics committee.
Procedures
Load-Velocity Profiling. All subjects were familiarized with the
equipment and testing procedures 1 week before data collection.
Testing procedures were completed in dry conditions on an out-
door 4G artificial turf field. A randomized counter balance design
was implemented on each test day. Subjects abstained from high-
intensity training in the 24 hours before the testing session. Subjects
wore running shoes and comfortable clothing. A radar device
(Model: Stalker ATS II; Applied Concepts, Dallas, TX) collecting
data at 46.9 Hz was positioned 10 m directly behind the starting
position and at a vertical height of 1 meter to approximately align
with the subject’s center of mass as per the recommendations of
Simperingham et al. (33).
Subjects started from a standing split stance position and
sprinted in a straight line for a distance of 30 m with maximal
effort for unresisted efforts and 20 m for resisted efforts. Sub-
jects were instructed to sprint through a set of cones that were
placed 2 m past the target distance to ensure deceleration was
avoided. After pilot testing, distances were chosen to ensure
Vmax was achieved without inducing fatigue. In all sessions,
subjects performed a standardized dynamic warm-up and 2
submaximal effort sprints (70 and 90% of self-determined
maximal intensity) before completing maximal effort sprints. A
Resisted Sled-Pull Training on Sprint Force-Velocity Profile (2020) 00:00
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minimum of 4 minutes of passive recovery was given between
each sprint (unresisted and resisted). Velocity-time data were
gathered through radar using the manufacturer provided soft-
ware (STATs software, Stalker ATS II Version 5.0.2.1; Applied
Concepts) throughout each sprint.
Unresisted Sprinting Protocol. Subjects were instructed to ap-
proach the start line and stand in a split stance with their preferred
foot forward. Subjects were instructed to sprint as fast as possible
with verbal encouragement given throughout each sprint.
Resisted Sled Pulling Protocol. Subjects started with an identical
set up, instructions, and cues as per the unresisted sprints. A
heavy-duty custom-made pull sled (8.7 kg) was placed 3.3 m
behind the subject attached to a waist harness by a nonelastic
nylon tether. Subjects were instructed to take up all the slack in the
tether to ensure no bouncing or jerking as they initiated the sprint.
Again, subjects were instructed to sprint as fast as possible with
verbal encouragement given throughout each sprint. The first
resisted trial used an absolute load of 27 kg, which included the
weight of the sled. Subjects then completed 3 additional loads,
increasing in increments of 20 %BM. The load range was based
on pilot testing, which determined the range of loads that reduced
an athlete’s velocity by values above and below 50% of unresisted
Vmax, to provide a broader spectrum of loading parameters and
an accurate fit of the linear load-velocity profile
Load-Velocity Relationship and Load Optimization. Maximum
velocity was obtained for each unresisted and resisted trial. The
individual load-velocity (LV) relationship was established for
each subject and checked for linearity. The linear regression of the
load-velocity relationship was then used to establish the load that
corresponded to a velocity decrement of 25, 50, and 75%, with
the slope of the line explaining the relationship between load and
velocity. An example of the raw data gathered from 1 subject
unresisted and resisted trials, and its plotted data at correspond-
ing velocity decrements is shown in Figure 1A. As shown in
Figure 1B, mean loads of 44 64 %BM, 89 68 %BM, and 133 6
12 %BM corresponded to light, moderate, and heavy for a ve-
locity decrement of 25, 50, and 75%, respectively.
Preintervention and Postintervention Testing. Jump testing con-
sisted of both horizontal and vertical jump measures (cm). Both
protocols have been shown to be reliable in assessing jump per-
formance in youth (9,15). During the standing long jump, sub-
jects were asked to stand on the start line and jump horizontally as
far as possible and then to hold their landing position. A tape
measure was then used to measure the jump distance from the
start line to the rear most heal of the foot on landing. The coun-
termovement jump used a self-selected depth in which subjects
were instructed to jump vertically as high as possible and to keep
their legs extended while in the air. The jump height was calcu-
lated from the flight time (FT) using an optical measurement
Figure 1. A) An example of the load-velocity relationship for 1 subject. The raw data () shows
the maximum velocity (m·s
21
) achieved during resisted and unresisted sprints. Using the linear
relationship between load and velocity, the arrows shows the calculated loads corresponding
to a 25, 50, and 75% decrement in velocity. B) The linear mean load-velocity relationship for all
subjects with the loads that correspond to a decrement in velocity of 25, 50, and 75%,
representing speed-strength, power, and strength-speed training zones.
Resisted Sled-Pull Training on Sprint Force-Velocity Profile (2020) 00:00 |www.nsca.com
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system (Optojump, Microgate, Italy). Acceleration sprint testing
was assessed using a radar gun, with the set up as per the load-
velocity testing except that it took place indoors in a controlled
environment over 22 m. The same software provided by the radar
device manufacturer used during load-velocity testing was used to
collect raw velocity data (V
max
) during each sprint and then fitted
with an exponential function. Instantaneous velocity was derived
to calculate net horizontal force and power (Pmax). Each linear
force-velocity relationship was then extrapolated to calculate
theoretical maximum force (F
0
). This method has been shown to
be a reliable field method to assess force-velocity profiles during
over ground sprinting (31). Sprint force-velocity profiles were
then constructed using custom-made LabVIEW software. Con-
tact time (CT) and FT during the acceleration phase was captured
during both pretesting and post-testing at the second and third
steps of the unresisted sprint using an Apple iPhone 6 (Apple,
Cuptertino, CA). Video footage was analyzed frame by frame
with QuickTime Player 7 Pro for Mac (Apple Inc.).
Training Intervention. Subjects were matched by speed and ran-
domly allocated between 1 unresisted and 3 resisted groups;
unresisted (n512), light (n515), moderate (n514), and heavy
(n512) corresponding to a Vdec of 0, 25, 50, and 75% of
maximum sprint velocity. The training intervention consisted of 2
resisted sprint sessions immediately followed by a strength session
in the weight room. Subjects were provided at least 48 hours
recovery time between training days. In addition, 2 sport practice
sessions were completed on separate days during the week. All
athletes abstained from high-intensity activity for 24 hours before
each sled-pull training session. Both resisted sprint and strength
training protocols followed a linear periodization model, which
involved a standard 3:1 mesocycle arrangement (i.e., 3 weeks of
increasing intensity followed by 1 week of reduced workload)
being completed for 2 consecutive 4-week mesocycles. With the
exception of their sport practice and specific sled loading using
during the sprint training sessions, all groups preformed identical
strength training programs. Specific sets and repetitions for
resisted sprinting and weight room exercises are provided in
Tables 1 and 2, respectively.
The sled load, sprint distance, and rest interval of 3 minutes per
repetition remained constant for each subject throughout the
training intervention. The total work was equated for all resisted
groups to that of the unresisted control group by reducing the
distance per rep by the same percentage Vdec caused by sled
loading. This resulted in sprint distances of 22.5, 15, and 7.5 m
for the training groups loaded to cause a Vdec of 25, 50, and 75%
Table 1
Sets, reps, and weekly total distances for unresisted, light, moderate, and heavy training groups.*
Week
Unresisted Light (speed-strength) Moderate (power) Heavy (strength-speed)
Reps
p·w
21
Distance per
rep (m)
Total
distance
p·w
21
Reps
p·w
21
Distance per
rep (m)
Total
distance
p·w
21
Reps
p·w
21
Distance per
rep (m)
Total
distance
p·w
21
Reps
p·w
21
Distance per
rep (m)
Total
distance
p·w
21
1 6 30 360 6 22.5 270 6 15 180 6 7.5 90
2 7 30 420 7 22.5 315 7 15 210 7 7.5 105
3 8 30 640 8 22.5 360 8 15 240 8 7.5 120
4 6 30 360 6 22.5 270 6 15 180 6 7.5 90
5 7 30 420 7 22.5 315 7 15 210 7 7.5 105
6 8 30 480 8 22.5 360 8 15 240 8 7.5 120
7 9 30 540 9 22.5 405 9 15 270 9 7.5 135
8 7 30 420 7 22.5 315 7 15 210 7 7.5 105
*p·w
21
5per week, m 5meters.
Table 2
Progressive weight room training program for strength performed by all 4 groups during the 8-week training intervention.*
Weeks 1–4 Weeks 5–8
Exercise Sets Reps Exercise Sets Reps
SESSION 1
A1 DB RFESS 3–5 5 BB RFESS 3–5 3
A2 Corrective 3 10 Corrective 3 10
B1 DB bench press 3 8–10 BB bench press 3 6–8
B2 Glute ham iso hold 3 20 s Glute ham raise 3 6–8
C1 DB farmers carry 2 20 m DB farmers carry 2 20 m
C2 Inverted row 2 10–12 Weighted inverted row 2 8–10
C3 Core stability 2 30–60 s Cable rotation twist 2 8–10
SESSION 2
A1 BB glute raise 3–5 5 BB glute raise 3–5 3
A2 Corrective 3 10 Corrective 3 10
B1 Chin up 3 8–10 Weighted chin up 3 3–5
B2 SL pistol squat 3 8–10 Weighted step up 3 6
C1 DB overhead carry 2 20 m DB overhead carry 2 20 m
C2 Push up 2 10–12 Weighted push up 2 8–10
C3 Core stability 2 30–60 s Hanging leg raise 2 8–10
*RFESS 5rear foot elevated split squat; BB 5barbell; DB 5dumbbell; iso 5isometric; SL 5single leg; m 5meters.
Resisted Sled-Pull Training on Sprint Force-Velocity Profile (2020) 00:00
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and meant that sprint efforts lasted approximately the same du-
ration across subjects in all training groups. All subjects had 3
minutes rest between maximal sprint efforts.
Before each training session all subjects performed a stan-
dardized 10-minute dynamic warm-up was completed, inclusive
of submaximal repetitions of sprinting and dynamic mobilization
and activation exercises targeting the main muscle groups of the
upper and lower extremities. On completion of the warm-up, all
athletes performed sprint training specific to their training group.
Statistical Analyses
Descriptive statistics (mean 6SD) and effect size statistics are
reported for all dependent variables of jump and sprinting per-
formance. The data met the criteria for normality and homoge-
neity. A 4 32 (group 3time) repeated-measured analysis of
variance with Bonferroni post-hoc comparisons was used to de-
termine the within-group and between-group effects for each
dependent variable as well as examining interaction effects. An
alpha level of p,0.05 was used to indicate the statistical sig-
nificance. Effect sizes (Cohen’sd) were used to quantify the
magnitude of the performance change in each group, with values
of 0.20, 0.60, and 1.20 representing the qualitative thresholds for
trivial, small, moderate, and large effects, respectively (11).
Bayesian statistics were used to further investigate the relative
change from pretest to post-test for all jump and sprint perfor-
mance variables. The Bayesian approach considers the un-
certainty about expected values and variance as distributions
conditioned on the data to create observation models and then a
probability distribution that a player will improve performance
with a given training condition (assuming all players are similar to
begin with). Using the Jeffreys prior for parameter estimates,
posterior probability of performance improvements for each
group and their 95% credible intervals were calculated. Jeffreys
prior was used because there was no previous information
available regarding expected values and variance before data
collection, whereas Jeffreys posterior was used to maximize the
information gathered from data collection.
Results
Means 6SD and magnitude of within-group changes for all
variables in all conditions preintervention and post-
intervention are shown in Table 3. For all variables, there were
no significant differences between groups at baseline (p.
0.05). Results in Table 3 show that there were main effects of
time for all split times, CT on the second step, F
0
, and Pmax (all
p,0.01), whereas Vmax was the only variable to report a
significant interaction effect (p,0.05). However, there were
clear trends for different responses across the groups when
assessing the within-group changes. For the jumps, only the
light group significantly improved height (d50.26). However,
the effect of the resisted sled pulling was more marked on the
horizontal jump measures with both moderate and heavy
groups significantly improving jump performance (d5
0.22–0.48).
All resisted interventions demonstrated significant within-
group improvements for 0–5, 0–10, and 0–20 m sprint times.
Across 5, 10, and 20 m sprint times there is a clear trend of an
increasing effect as load increases; with unresisted sprinting
leading to trivial to small improvements (d 5#0.24), light
loading leading to small improvements (d 5;0.43), moderate
loading leading to small to moderate improvements (d 5
0.48–0.71), and heavy loading leading to moderate improve-
ments (d 50.84–1.04). No significant difference occurred in any
group from 5 to 10 m, whereas split times between 10 and 20 m
significantly improved in unresisted, light, and moderate groups
but not in the heavy group. No significant differences were ob-
served for any step kinematics, although effect sizes for CT and
FT were shown to increase with sled load from trivial to small (d
50.00–0.44).
Regarding force-velocity profiling, there were significant positive
within-group improvements for Pmax for all resisted interventions
with moderate effect sizes observed in moderate (d51.03) and
heavy (d50.78) sled interventions. The cumulative effect of these
changes was that Pmax reflected changes in sprint times. A similar
trendwasobservedwithF
0
where significant within-group differ-
ences and moderate effect sizes (d 51.08–1.19) were observed in the
Table 3
Mean 6SD for all measured variables preintervention to postintervention in youth athletes completing 8 weeks of either unresisted, light,
moderate, or heavy resisted sprint training.*
Unresisted Light Moderate Heavy
Pre Post ES Pre Post ES Pre Post ES Main Interaction Es
VJ (cm) 38.7 65.8 39.2 64.8 0.08 43.1 66.0 44.8 66.3§ 0.26 40.9 67.2 41.2 66.9 0.04 42.9 67.8 44.3 67.3 0.18
SLJ (cm)† 208 615 208 613 0.01 225 622 230 621 0.22 204 619 213 619‖0.47 215 622 223 623§ 0.34
0–5 m (s)† 1.6 60.12 1.60 60.15 0.01 1.57 60.15 1.51 60.08§ 0.43 1.63 60.13 1.54 60.11‖0.71 1.62 60.10 1.50 60.09‖0.84
0–10 m (s)† 2.42 60.16 2.40 60.17 0.12 2.36 60.18 2.29 60.12§ 0.40 2.45 60.18 2.34 60.14‖0.58 2.42 60.12 2.29 60.11‖1.04
0–20 m (s)† 3.84 60.24 3.79 60.23 0.24 3.73 60.27 3.62 60.19‖0.41 3.85 60.26 3.72 60.19‖0.48 3.77 60.15 3.64 60.16‖0.87
5–10 m (s)† 0.83 60.05 0.81 60.04 0.39 0.79 60.05 0.78 60.05 0.20 0.81 60.06 0.80 60.04 0.21 0.80 60.05 0.79 60.04 0.18
10–20 m (s)† 1.42 60.10 1.38 60.08‖0.40 1.37 60.09 1.33 60.08‖0.38 1.40 60.09 1.38 60.07§ 0.25 1.35 60.06 1.35 60.07 0.11
2nd step CT (s)† 0.17 60.01 0.18 60.00 0.23 0.18 60.01 0.18 60.01 0.30 0.17 60.01 0.17 60.01 0.40 0.17 60.01 0.18 60.01 0.42
3rd step CT (s) 0.16 60.01 0.16 60.01 0.04 0.17 60.00 0.16 60.01 0.43 0.16 60.01 0.16 60.01 0.00 0.15 60.01 0.16 60.01 0.39
FT (s) 0.08 60.01 0.08 60.01 0.04 0.06 60.00 0.06 60.01 0.08 0.07 60.01 0.07 60.01 0.18 0.07 60.01 0.06 60.01 0.44
F
0
(N·kg
21
)† 5.5 61.0 5.6 61.1 0.09 5.9 61.4 6.1 61.1 0.22 5.2 60.7 6.0 61.1‖1.08 5.3 60.8 6.3 60.8{1.19
V
max
(m·s
21
)‡ 8.18 60.44 8.35 60.59 0.33 8.37 60.61 8.60 60.66 0.35 8.31 60.56 8.24 60.55 0.12 8.78 60.79 8.43 60.69§ 0.44
P
max
(W·kg
21
)† 11.5 62.0 11.8 62.0 0.18 12.7 62.7 13.6 62.5§ 0.39 11.3 61.3 12.6 61.7{1.03 12.1 61.9 13.6 61.9{0.78
*VJ 5vertical jump, SLJ 5standing long jump, CT 5contact time, FT 5flight time, F
0
5maximal theoretical force, V
max
5maximal velocity, P
max
5maximal theoretical power.
†Significant main effect of time (p,0.01).
‡Significant interaction effect (p,0.05).
§Significant within group difference preintervention to postintervention (p,0.05).
‖Significant within group difference preintervention to postintervention (p,0.01).
{Significant within group difference preintervention to postintervention (p#0.001).
Resisted Sled-Pull Training on Sprint Force-Velocity Profile (2020) 00:00 |www.nsca.com
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moderate and heavy training and interventions. Conversely, a sig-
nificant reduction occurred for Vmax in the heavy group. Effect sizes
forVmaxweretrivialtosmallacrossallinterventionswiththe
greatest effect observed in the unresisted condition (d 50.12–0.44).
An illustration of the change in velocity over distance and in the
force-velocity profile from pretraining to post-training in each group
can be observed in Figures 2 and 3, respectively.
The mean estimated posterior probability of performance im-
provements for each test variable along with their 95% credible
intervals are shown in Table 4, with variables with a probability of
Figure 3. Prechanges to postchanges in force velocity profiles after an 8-week sled-pull training intervention at unresisted,
light, moderate, and heavy loads.
Figure 2. Prechanges to postchanges in velocity profiles after an 8-week sled-pull training intervention at unresisted, light,
moderate, and heavy loads.
Resisted Sled-Pull Training on Sprint Force-Velocity Profile (2020) 00:00
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improvement .0.75 highlighted in gray. Overall the results confirm
that a greater number of variables demonstrated higher probabilities
of improvement with increasing load. A higher probability of im-
proved sprint performance, particularly acceleration, was evident at
heavier loads in comparison with unresisted or lighter loads. Simi-
larly, the probability of improvement across kinetic sprint variables
was generally higher in the moderate and heavy groups. However, a
decrease in the probability of Vmax improving was evident at
heavier loads.
Discussion
The main finding of this study was that moderate to heavy loads
resulted in increased sprint performance, particularly during the
initial acceleration phase, when compared with unresisted or
lighter loads. Changes in sprint split times were reflected in force-
velocity profiles, with heavy and moderate sled-pull training
significantly improving F
0
and Pmax, whereas unresisted and
lighter loads resulted in small improvements in V
max
. These
findings suggest that changes in the sprint force-velocity profile
are specific to the training stimulus used, with heavy sled pulling
being particularly effective at improving F
0
and acceleration
over 5 m.
Sprint-specific training transferred minimal gains to vertical
jump performance, with only the light resisted training group
making significant but small gains in performance. Conversely,
horizontal jump performance significantly improved with mod-
erate and heavy resisted sprint training, with those groups also
making the largest improvement in sprint performance. This
supports the notion that horizontal jumps are more strongly re-
lated to sprint performance than vertical jump performance (18).
The findings also demonstrate the differential effects of resisted
sprint training with different loads on jump performance. These
differential effects might be related to the amount of vertical and
horizontal force produced with increasing loads, with heavier
loads leading to a greater horizontal orientation of force (25).
Therefore, heavy loading through horizontal strength training
can be incorporated as a training method to aid horizontal jump
performance.
A recent review by Petrakos et al. (26) suggested more sprint
training interventions are needed across an array of sled loads to
determine the effectiveness of resisted sprint training in compar-
ison with unresisted sprinting. One study examining a single
training load of 80% BM and an unresisted control group, found
resisted sprinting superior in increasing 5-m and 20-m sprint
performance in adult soccer players (23). Findings from the cur-
rent study agree with the limited research available; notably, all of
the resisted-sprint groups had significant within-group improve-
ments in sprint times that ranged from small to moderate in effects
size. Interestingly, the magnitude of those effects was greatest over
the initial 5 m and increased with greater loading. This indicates
that resisted sprinting affected the first step and acceleration
phase, particularly in the groups working with moderate and
heavy sled loads. These results are also in line with the limited
previous research favoring heavier loads over lighter loads in
decreasing 5-m sprint times (2,12). Gains in sprint performance
beyond 5 m were largely the result of the improvement in the
initial acceleration phase after moderate and heavy training.
Changes in the velocity-distance profiles in Figure 2 clearly show
training with different resistance influenced the training adapta-
tions, which was reflected in the ability of training at moderate
and heavy loads to significantly increase both F
0
and Pmax.
However, velocity in the heavy group slightly decreased toward
the end of the 20-m sprint reflecting the decreased Vmax post-
training.
The differential effects of sprint training with either no load or
increasing levels of load and the influence on acceleration, speed,
and horizontal force suggest specificity of training influences
force-velocity profiles. Unresisted and light loads slightly in-
creased V
max
, whereas the opposite occurred at moderate to
heavy loads leading to a significant interaction effect. V
max
was
significantly reduced at heavy loads. However, F
0
was improved
in the moderate and heavy resisted sled training. Pmax did not
change with unresisted sprinting, although, small changes were
observed with light resistance and moderate changes with mod-
erate and heavy resistance. The current study supports previous
research by Cross et al. (8) and Morin et al. (23) that training
responses are specific to the loading used during resisted-sprint
training, leading to specific adaptations across the sprint force-
velocity spectrum. Results suggest young athletes will improve
their initial acceleration and associated underlying mechanical
determinants (F
0
and Pmax). Training programs with an em-
phasis on improving initial acceleration for team sports athletes
Table 4
Posterior probability (credible interval) of performance variable improvements after unresisted sprint training and resisted sprint training
with light, moderate, and heavy resisted sled pulling.*†
Unresisted Light Moderate Heavy
Probability (95% credible interval)
VJ 0.58 (0.36–0.78) 0.73 (0.53–0.88) 0.47 (0.27–0.68) 0.65 (0.42–0.84)
SLJ 0.50 (0.29–0.72) 0.67 (0.47–0.83) 0.74 (0.54–0.89) 0.78 (0.57–0.93)
0–5 m 0.49 (0.36–0.78) 0.70 (0.36–0.78) 0.81 (0.36–0.78) 0.80 (0.36–0.78)
0–10 m 0.54 (0.33–0.75) 0.73 (0.53–0.88) 0.79 (0.59–0.92) 0.80 (0.58–0.94)
0–20 m 0.62 (0.40–0.82) 0.78 (0.59–0.92) 0.79 (0.59–0.93) 0.79 (0.57–0.94)
5–10 m 0.72 (0.50–0.89) 0.59 (0.39–0.77) 0.61 (0.40–0.79) 0.59 (0.36–0.79)
10–20 m 0.77 (0.55–0.93) 0.81 (0.62–0.94) 0.69 (0.48–0.86) 0.56 (0.35–0.77)
2nd Step CT 0.66 (0.44–0.85) 0.60 (0.39–0.72) 0.68 (0.44–0.86) 0.79 (0.64–0.95)
3rd Step CT 0.50 (0.28–0.71) 0.37 (0.18–0.59) 0.51 (0.30–0.73) 0.67 (0.42–0.87)
FT 0.41 (0.21–0.63) 0.47 (0.26–0.69) 0.52 (0.31–0.73) 0.58 (0.34–0.80)
F
0
0.51 (0.30–0.73) 0.68 (0.48–0.84) 0.80 (0.61–0.93) 0.79 (0.56–0.93)
V
max
0.33 (0.14–0.56) 0.32 (0.15–0.52) 0.56 (0.36–0.75) 0.69 (0.47–0.87)
P
max
0.59 (0.37–0.79) 0.78 (0.59–0.92) 0.81 (0.62–0.94) 0.80 (0.58–0.94)
*VJ 5vertical jump, SLJ 5standing long jump, CT 5contact time, FT 5flight time, F
0
5maximal theoretical force, V
max
5maximal velocity, P
max
5maximal theoretical power.
†Bolded cells show those variables with a probability .0.75.
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should preferentially train with relatively heavy loading regimes.
This finding is in line with review work by Lesinski et al. (14),
which concluded that non–sprint-specific resistance training in a
vertical plane of motion was most effective for young athletes
when completed at heavy loads corresponding to 80–89% of 1-
repetition max. The additional resistive stimulus at heavier loads
during sled pulling in a horizontal plane of motion combined with
the potential of adolescent athletes to increase force application
seems to provide an optimum training scenario to improve ac-
celeration. However, practitioners may want to ensure gains in
acceleration are not at the expense of maximal sprint speed, in
which case young athletes may need to be exposed to sprint
training with no or lighter loads.
Probability statistics confirmed that subjects were more likely
to experience positive improvements in performance when
working against heavier loads. The number of variables showing
a probability of improvement .0.75 was 1 for unresisted
sprinting, 3 for training with a light resistance, 5 variables with a
moderate resistance, and 7 variables with a heavy resistance. The
probability of acceleration performance improvement was much
greater in light, moderate, and heavy groups (21, 31, and 30%)
compared with unresisted sprinting. This improved sprint per-
formance has been observed previously (23), however, this is the
first intervention study to use loads across 3 different zones of
training at 25, 50, and 75% of velocity decrement in any pop-
ulation, and the first resisted sprint training study to go above a
resistance of 10%BM in young athletes. Although subjects were
familiar with resisted sled pulling, this was the first cumulative
training block of such sprint-specific training. The novelty of a
horizontal strength training stimulus at such heavy loads applied
to a cohort at a stage of maturation (;peak weight velocity) in
which adaptation to resistance training has been shown to pro-
duce favorable results proved to be beneficial (22). The findings
suggest that practitioners will increase the probability of im-
proving sprint performance, specifically initial acceleration by
using heavier sled loads than previously studied in young athletes.
It may be that those probabilities can be further improved by
matching the resistance and training zone to an athlete’s initial
force-velocity profile (8), however, further research is needed to
confirm this.
Although the findings of this study demonstrate that high-
school athletes can benefit from resisted sled pull training, par-
ticularly with heavy loads, some caution should be taken when
applying findings to other populations. It has previously been
shown that prepubertal children do not respond as well to resisted
sprint training as adolescent youth athletes (28). It should also be
noted that all subjects in this study had a history of engaging in
resistance training and had some familiarity with resisted
sprinting; this may be important in preparing young athletes to
undertake resisted sprinting with heavier loads. Although sled
pulling did improve acceleration, force, and power, it did not
improve V
max
. Collectively, the above suggest the need for youth
athletes to be engaging in a variety of different training modes to
support the overall development of acceleration and maximal
sprint speed as well as other athletic qualities.
The aim of this study was to assess the effectiveness of unre-
sisted and resisted sled-pull training at light, moderate, and heavy
loads in high-school athletes. Although all groups exhibited im-
provements, there was a clear trend for greater and more con-
sistent adaptations with heavier sled loads within a strength-
speed zone of training. Changes in sprint performance and
velocity-distance profiles were also specific to the force-velocity
stimulus of training, with the unresisted and light training group
making slight gains in Vmax, all resisted groups improving sprint
times and Pmax, and moderate and heavy training groups in-
creasing F
0
. Cumulatively, the results show that the greatest gains
in short distance sprint speed was made in response to training
against heavier external resistances at or in excess of 50% Vdec.
Practical Applications
Post-PHV men with a limited history of resisted sprinting seem
to respond favorably to moderate and heavy resisted sprint
loads over the course of a short-term training intervention.
Thus, in addition to facilitating the correct teaching of accel-
eration mechanics, heavier external loads may reap the
greatest benefits in improving sprint acceleration in as little as
8 weeks of training. The manner in which chronic exposure to
resisted sprinting within a longitudinal, periodized training
plan influences force-velocity-power (F-V-P) characteristics
remains unknown; however, practitioners are encouraged to
routinely manipulate the resisted loading to foster ongoing
adaptation in performance. The current study also supports
the notion of adaptations being specific to the imposed de-
mands, with heavier loads appearing to favor horizontal force
production during the early acceleration phase (0–10 m),
whereas lighter loads and unresisted sprinting benefitting the
later phases of acceleration (10–20 m) and maximum velocity.
Thus, much like other aspects of strength and conditioning
provision, practitioners are encouraged to prescribe resisted
sprinting in light of the unique F-V-P needs of the young
athlete (i.e., increase F
0
or Vmax).
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