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EFFECTS OF VEST LOADING ON SPRINT KINETICS
AND KINEMATICS
MATT R. CROSS,
1
MATT E. BRUGHELLI,
1
AND JOHN B. CRONIN
1,2
1
Sports Performance Research Institute New Zealand, Auckland University of Technology, Auckland, New Zealand; and
2
School of Exercise, Biomedical and Health Science, Edith Cowan University, Perth, Australia
ABSTRACT
Cross, MR, Brughelli, ME, and Cronin, JB. Effects of vest
loading on sprint kinetics and kinematics. J Strength Cond Res
28(7): 1867–1874, 2014—The effects of vest loading on sprint
kinetics and kinematics during the acceleration and maximum
velocity phases of sprinting are relatively unknown. A repeated
measures analysis of variance with post hoc contrasts was
used to determine whether performing 6-second maximal exer-
tion sprints on a nonmotorized force treadmill, under 2
weighted vest loading conditions (9 and 18 kg) and an un-
loaded baseline condition, affected the sprint mechanics of
13 males from varying sporting backgrounds. Neither vest load
promoted significant change in peak vertical ground reaction
force (GRF-z) outputs compared with baseline during acceler-
ation, and only 18-kg loading increased GRF-z at the maximum
velocity (8.8%; effect size [ES] = 0.70). The mean GRF-z sig-
nificantly increased with 18-kg loading during acceleration and
maximum velocity (11.8–12.4%; ES = 1.17–1.33). Horizontal
force output was unaffected, although horizontal power was
decreased with the 18-kg vest during maximum velocity
(214.3%; ES = 20.48). Kinematic analysis revealed decreas-
ing velocity (23.6 to 25.6%; ES = 20.38 to 20.61), decreas-
ing step length (24.2%; ES = 20.33 to 20.34), increasing
contact time (5.9–10.0%; ES = 1.01–1.71), and decreasing
flight time (217.4 to 226.7%; ES = 20.89 to 21.50) with
increased loading. As a vertical vector-training stimulus, it seems
that vest loading decreases flight time, which in turn reduces
GRF-z. Furthermore, it seems that heavier loads than that are
traditionally recommended are needed to promote increases in
the GRF-z output during maximum velocity sprinting. Finally, vest
loading offers little as a horizontal vector-training stimulus and
actually compromises horizontal power output.
KEY WORDS vest loading, sprint mechanics, horizontal force,
vertical force, acceleration, maximum velocity
INTRODUCTION
An athlete’s ability to accelerate and attain maxi-
mal velocity is reliant on the relationship between
the force production capability of the body and
the ability of the athlete to harness and effectively
use that force in time periods relative to the activity (7).
Furthermore, it has been proposed that the direction of force
application plays a larger role in increasing the acceleration
than the amount of force applied (24) and that greater accel-
erations and maximal velocities have been achieved through
lower but more forward-oriented forces (18,23,24).
Retaining a high ratio of horizontal to total force production
seems to be key to enhance acceleration and maximum
velocity (24). Understanding which training techniques
may present such mechanical overload would seem impor-
tant to optimize the development of these speed qualities.
Resisted sprint techniques, such as sled or vest weighted
sprinting, offer a specific approach to overloading during
common sport movements. (1,5,11,21,22). Potentially, these
techniques could elicit positive effects on sprint kinematics (i.
e., contact time, flight time, step length, and step frequency)
by increasing the athlete’s ability to generate vertical and
horizontal forces. Although studies examining the acute
and longitudinal effects of sled towing on sprint performance
are increasingly common, there are few studies that examine
the effects of vest loading on similar performance character-
istics (6,8). Notably, it has been suggested that sled towing
and vest loading may overload the neuromuscular system in
a different manner. For example, sled towing, particularly at
higher percentages of body mass (BM) (16), has been pro-
posed to offer a greater horizontal vector-training stimulus
whereas vest sprinting is more vertically oriented (7). Under-
standing the mechanical adaptations associated with vest
loading in greater detail is of interest to these researchers.
It has been suggested that the heavier the external loading,
the greater disruption to normal sprint kinematics—therefore,
in best practice, the optimal loading for sprinting would be
one that minimally affects running mechanics, while supply-
ing an appropriate overload stimulus to promote adaption
(2,22). To date, only 3 recent articles have examined the use
of weighted vests on sprint performance and kinematics
(2,6,8). Of these studies, 2 examined the acute effects of vest
loading (9–20% of BM) on sprint kinematics and reported
Address correspondence to Matt R. Cross, cross.matt.r@gmail.com.
28(7)/1867–1874
Journal of Strength and Conditioning Research
Ó2014 National Strength and Conditioning Association
VOLUME 28 | NUMBER 7 | JULY 2014 | 1867
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a decrease in velocity (23.8%) and an increase in sprint time
(7.5–11.7%) with loading in comparison with unresisted con-
ditions (2,8). In addition, vest sprinting has been shown to
affect step/stride length (20.5 to 25.2%) and frequency
(22.4 to 22.7%) and several other kinematic variables in
comparison with unloaded sprinting (2,8). A study by Bosco
et al. (3), highlighted the ability to increase power through
periodization involving external loading around the torso in
the form of a weighted belt. However, as can be observed from
this brief treatise of the litera-
ture, the kinetics-associated vest
loading is relatively unexplored,
and there is certainly no research
profiling kinetics across a variety
of vest loads.
The acceleration and maxi-
mum velocity phases of sprinting
require different mechanical de-
mands on the sprinter (7,9). The
acceleration phase requires long
contact periods, short flight
times, positive net horizontal
forces, and a greater forward
trunk lean in comparison with
the maximum velocity phase
(1,9). Thus, each phase may
respond differently to the same
vest load and therefore warrant
specific loading protocols
(1,9,28). No previous studies
have examined the effects of
vest sprinting on acceleration
or maximum velocity phase kinetics during sprint running.
Thus, the means of effectively manipulating vest load to cause
changes in the force profile for specific adaptation is currently
unknown. Such information is important to strength and con-
ditioning and sprint coaches for programming purposes. The
aim of this study, therefore, was to analyze the effects of vest
loading on sprint kinetics and kinematics during the acceler-
ation and maximum velocity phases while sprinting on a non-
motorized treadmill (NMT) ergometer.
METHODS
Experimental Approach to
the Problem
A cross-sectional design was
used to investigate the effects
of vest loading on kinematics
and kinetics during accelera-
tion and maximum velocity
sprinting. All subjects per-
formed maximum effort
6-second sprints on an NMT
with and without vest loading
(9and18kg).Dataduringthe
first 2 steps (i.e., first stride) of
the 6-second sprint and 10
steps once the subjects at-
tained maximum velocity
were averaged for final values.
Data were then compared
using a repeated measures
analysis of variance (ANOVA)
with Bonferroni post hoc
Figure 1. Image of sprint trial on the nonmotorized treadmill under braking load.
Figure 2. Image of treadmill set-up and foot braking of belt.
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analyses to determine statistical difference between
conditions.
Subjects
Thirteen sport-active (rugby codes, n= 6; track sprinters, n=2;
field hockey n= 1; miscellaneous sporting codes, n=4),
weightlifting, healthy male
university-level athletes volun-
teered to take part in this study
(22.9 63.3 years old; BM:
82.5 68.4 kg; stature: 179.1 6
6.6 cm). All athletes provided
written informed consent before
participating, and completed a
health questionnaire to ensure
that they were fit for testing.
The Institutional Ethics Com-
mittee of Auckland University
of Technology provided
approval for this study.
Procedures
Equipment. A Woodway Force
3.0 (Eugene, OR, USA) NMT
ergometer was used to quantify the sprint kinetics and
kinematics (Figure 1). This ergometer is a modernized equiv-
alent of the original NMT system introduced by Lakomy
(19) and has been implemented (4,25) and validated (12).
Nonmotorized treadmill ergometry pertaining to both the
training and measurement of performance variables have
Figure 3. A representative sprinting velocity-time curve during a 6-second maximum effort sprint.
Figure 4. A representative GRF-z-time curve during a 6-second maximum effort sprint. The arrows indicate the first 2 steps (i.e., first stride) during the
acceleration phase and the 10 steps during maximum constant velocity.
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been explored in depth during sprinting (13–15,20,26,27).
The NMT system used in this study featured a user-driven
vulcanized rubber belt, the mechanics of which feature 12
guiding rollers and 114 ball bearings. The subjects were har-
nessed around the waist to a vertical strut at the rear of the
system. A nonelastic tether secured the harness to a load cell
and a locking vertical-sliding gauge allowed the collection of
horizontal force data. This sliding gauge was manually
adjustable (and securable) to each subject’s hip height to
enable horizontal alignment of the tether to the load cell
during running trials. Calibration of the load cell took place
before the testing session by hanging a selection of known
weights from the tether as instructed by the manufacturer.
Vertical force output was collected using 4 load cells posi-
tioned beneath the NMT belt. The vertical load cells were
calibrated before and after testing using known loads placed
on top of the stationary treadmill belt. The velocity of the
treadmill belt was collected by 2 optical speed microsensors
located at the rear of the treadmill belt. Calibration for this
measurement was not needed because the distance recorded
per rotation of the belt did not change, and unit conversion
was hardcoded into the NMT software. Power output was
measured by the NMT as the product of the force exerted on
the horizontal load cell and the velocity of the treadmill belt.
All variables were collected at a sampling rate of 200 Hz,
using a hardwired system interface (XPV7 PCB; Fitness
Technology, Adelaide, Australia). Primary analysis took
place within a custom-built LabVIEW software program
(LabVIEW; National Instruments, Texas, USA).
Resisted Conditions. Weighted vests were used to supply the
vertical loading, and each subject performed the trials as
usual on the NMT system. The vests were loaded with small
sandbags that could be added or removed in increments of
approximately 200 g. The load could be distributed evenly
around the subject’s torso, up to approximately 20 kg per
vest. The 2 loading conditions included absolute loads of
9 and 18 kg. Previous researchers have used vest loads
between 7 and 20% of relative BM (2,3,8), and the loads
chosen for this study align with such loading parameters.
Procedures. Participants were required to report on a single
day for approximately 2.5 hours of preparation, familiariza-
tion, and testing. Close-fitting sports clothing and running
shoes were worn throughout. First, the subjects’ height,
mass, and age were determined and recorded. The subjects
were then required to undergo a
standardized warm-up and
familiarization. Initially, the sub-
jects jogged unloaded on the
treadmill for 90 seconds. During
this time, the subjects were
encouraged to vary their pace
to familiarize themselves with
the feeling of accelerating on
the foreign running surface.
Two build-up sprints of 70 and
80% of the subjects’ expected
maximum velocity were then
performed based on the findings
of semi-professional Australian
Rules footballers sprinting on
an NMT (4). This consisted of
a 3-second submaximal acceler-
ation to the determined velocity,
holding that velocity for 5 sec-
onds, and then decelerating. To
conclude the warm-up protocol,
a 3-second maximum acceler-
ation was performed. This
entailed a tester applying a sta-
tionary brake to the treadmill
track to enable the subject to
lean against the harness so as
to simulate a block start. Based
on their performance in this step
of the protocol, subjects were
allowed the opportunity to
TABLE 1. Test-retest reliability based on coefficient of variation (CV) and
intraclass correlation (ICC) for sprint kinetics and kinematics.*
Baseline 9-kg vest 18-kg vest
CV (%) ICC CV (%) ICC CV (%) ICC
Velocity (m/s)
Peak 1.6 0.98 1.9 0.98 2.2 0.98
GRF-z (N)
Acceleration 3.1 0.98 3.8 0.97 7.0 0.86
Maximum velocity 1.8 0.99 2.9 0.99 3.4 0.98
GRF-z mean (N)
Acceleration 1.6 0.99 1.4 1.00 8.8 0.70
Maximum velocity 1.5 1.00 1.4 1.00 1.9 0.99
H
F
(N)
Acceleration 5.8 0.89 6.5 0.92 9.0 0.74
Maximum velocity 6.5 0.87 6.6 0.97 5.5 0.93
P
MAX
(W)
Acceleration 6.1 0.92 8.2 0.96 16.0 0.59
Maximum velocity 6.6 0.94 7.5 0.97 6.8 0.95
Contact time (ms)
Acceleration 5.6 0.82 4.6 0.88 5.2 0.88
Maximum velocity 2.8 0.89 4.5 0.63 2.9 0.89
Flight time (ms)
Acceleration 9.2 0.90 6.3 0.93 11.2 0.88
Maximum velocity 4.2 0.97 6.1 0.98 9.1 0.96
Step frequency (Hz)
Maximum velocity 2.1 0.94 3.2 0.93 2.1 0.96
Step length (m)
Maximum velocity 2.0 0.99 2.0 0.99 17.9 0.92
*GRF-z = peak vertical force; H
F
= peak horizontal force; P
MAx
= peak power output.
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complete another trial of the blocked-start. Between each sec-
tion of the warm-up, subjects were allowed to rest for 60
seconds, followed by a 2–4-minute rest period preceding the
first trial.
The data collection consisted of 6-second maximal
velocity sprints under the 3 conditions. As per the warm-
up protocol, the treadmill belt was blocked from behind
(Figure 2). Starting position for all sprints was standardized
with subjects starting with the right foot back, and then,
they were instructed to lean into the harness. Throughout
each 6-second trial, subjects were given continuous verbal
encouragement to promote maximal effort. The loading
protocols consisted of 2 absolute vest loads (9 and 18 kg).
One to three trials, dependent on the success of the initial
and subsequent collections, were performed for each con-
dition. If more than 1 trial was collected, the trial with the
highest maximum velocity was selected for analysis. The
participant order was staggered and randomized, 4–6 sub-
jects performed the testing protocol in a cycled format
to maximize time efficiency and concurrently allow each
subject appropriate rest. Rest between trials was less than
4 minutes for each participant after each trial.
Statistical Analyses
Data was collected during the acceleration and maximum
velocity phases of each 6-second sprint (Figure 3). The
“first stride” was defined as the first 2 steps after the initial
push-off. “Maximum constant velocity” was defined as the
10 steps after the maximum velocity was attained and
maintained. The first 2 steps during the acceleration phase
and 10 steps during the maximum velocity phase were
averaged for final analysis (Figure 4). Velocity measures,
peak horizontal force, peak GRF-z, mean GRF-z, and
power output were obtained from the LabVIEW program
as described previously. Contact time was determined from
thetime(inseconds)thetreadmillregisteredforceabove
0 N to the moment it returned to a null reading (i.e., 0–0 N).
Flight time was measured from the moment of last ground
contact of one foot to the moment of first contact of the
other foot. Stride frequency was determined by the follow-
ing formula: 1/(contact time + flight time). Stride length
was determined through the following formula: peak veloc-
ity/stride frequency.
Seven of the participants completed 2 trials at each
loading condition to determine test-retest reliability of the
sprint kinetics and kinematics
variables. Intraclass correlation
coefficient and coefficient of
variation were calculated for
each variable (Table 1). Means
and SDs were determined for
each variable under each loading
condition and were used as
measures of centrality and
spread of data. Normal distribu-
tion of the data was checked
using the Sharpio-Wilk statistic.
A repeated measures ANOVA
with Bonferroni post hoc con-
trasts was used to determine sig-
nificant kinematic and kinetic
differences between loads (body
weight, 9 and 18 kg) for each
condition (acceleration and
maximum velocity). All varia-
bles, excluding step length, step
frequency, and peak velocity,
were analyzed in both the accel-
eration and maximum velocity
phases. Statistical significance
criterion was set at an alpha
level of p#0.05. Additionally,
effect sizes (ES) were calcu-
lated using the following equa-
tion: ES = (high value2low
value)/((high value SD +low
value SD)/2). Effect sizes were
described as large (ES .1.2),
TABLE 2. Kinetic and kinematic variable outputs over the acceleration and
maximum velocity phases under loading protocols.*
Loading conditions
Baseline 9-kg vest 18-kg vest
Velocity (m/s)
Peak 5.86 60.54 5.65 60.56†5.53 60.55†
GRF-z (N)
Acceleration 1613 6175 1547 6210 1674 6177
Maximum velocity 1923 6259 1983 6304 2093 6229†
GRF-z mean (N)
Acceleration 990 697 1027 6120 1107 680†
Maximum velocity 1165 6130 1205 6146 1309 6117†
H
F
(N)
Acceleration 482 6109 453 678 452 693
Maximum velocity 270 678 272 681 253 665
P
MAX
(W)
Acceleration 1272 6413 1271 6362 1380 6380
Maximum velocity 1600 6544 1540 6560 1372 6416†
Contact time (ms)
Acceleration 222 618 213 628 225 615
Maximum velocity 169 67.9 179 612†186 612†
Flight time (ms)
Acceleration 45 610 36 617 33 66†
Maximum velocity 69 614 57 613†56 610†
Step frequency (Hz)
Maximum velocity 4.15 60.33 4.18 60.27 4.09 60.26
Step length (m)
Maximum velocity 1.42 60.19 1.36 60.17†1.36 60.16†
*GRF-z = peak vertical force; H
F
= peak horizontal force; P
MAx
= peak power output.
†Significantly different from baseline.
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moderate (0.6 ,ES ,1.2), small (0.2 ,ES ,0.6), and
trivial (ES ,0.2) (10).
RESULTS
Kinematic Variables
Peak velocity decreased significantly between both vest
conditions (23.6 to 25.63%; ES = 20.38 to 20.61) in com-
parison with baseline unloaded sprinting (Table 2). Step fre-
quency remained statistically unchanged by external loading;
however, step length significantly decreased in both vested
conditions (24.2% [both conditions]; ES = 20.33 to 20.34)
in comparison with baseline. Contact time during the acceler-
ation phase was statistically unchanged respective to the base-
line condition. During the maximum velocity phase, significant
increases in contact time (5.9–10.0%; ES = 1.01–1.71) com-
pared with baseline were observed in both vest conditions.
The 18-kg vest condition flight time during the acceleration
phase was significantly decreased (226.7%; ES = 21.50) com-
pared with baseline. During the maximum velocity phase, both
vest conditions resulted in significantly decreased flight time
(217.4 t o 218.8%; ES = 20.89 to 21.08).
Kinetic Variables
Peak GRF-z output during the acceleration phase was
statistically unchanged relative to the baseline condition.
During the maximum velocity phase, only the 18-kg vest
condition produced significantly greater peak GRF-z (8.8%;
ES = 0.70) as compared with the baseline. During both the
acceleration and maximum velocity phases, the 18-kg vest
significantly increased the mean GRF-z compared with the
baseline (11.8–12.4%; ES = 1.17–1.33). Vest loading had no
significant effect on horizontal force output in either the
acceleration or the maximum velocity phases. There were
no significant variations from baseline for power output dur-
ing the acceleration phase; however, during the maximum
velocity phase, the 18-kg vest condition resulted in a signifi-
cantly lower horizontal power output compared with the
unloaded baseline conditions (214.3%; ES = 20.48).
DISCUSSION
This is the first study, to the best of our knowledge, that has
investigated the effects of vest loading on sprint kinetics along
with sprint kinematics during the acceleration phase and
maximum velocity phase of sprinting. Both vest loads
significantly decreased the maximal velocity output. The
3.5% decrease with approximately a 10.9% load (9 kg) of
mean subject BM is comparable with the findings of Alcaraz
et al. (2) who reported a 3.8% decrease in velocity with a 9%
BM load. Moreover, Cronin et al. (8) reported a 9.3–11.7%
increase in 30-m sprint times with a vest load of 15–20%
BM. Vest loading seems to have similar effects on peak velocity
outputs on NMT ergometry as over-ground sprinting.
The effects of additional external loading on step frequency
and step length may explain the decrements in velocity
observed in this study. In over-ground running, vest or belt
loading has been reported to significantly reduce the overall
stride length, and typically decrease step frequency (2,8).
Furthermore, the added loading will usually increase the
ground contact time (2,8) and decrease the flight time (2)
during the gait cycle. The results from this study concur with
this trend, with the addition of external loading decreasing
step length (24.2%), increasing contact time at the maximum
velocity (5.9–10.1%), and decreasing the flight time during
both acceleration (226.7%) and maximum velocity phases
(217. 4 to 218.8%). The significant decrease in flight time
observed at maximum velocity may suggest that the added
vertical load supplied by the vest essentially limited the sub-
jects’ ability to propel their body into a flight phase.
The relationship between external loading and GRF-z
output is of interest, particularly to those wishing to overload
such forces for a specific training purpose. Interestingly, no
significant increases in peak GRF-z relative to baseline with
vest loading during the acceleration phase were observed in
this study. Moreover, only the 18-kg vest resulted in a large
increase in the mean GRF-z during acceleration (11.8%). It
would seem that vest loading might not be an appropriate
resisted method to overload the acceleration phase vertical
GRF-z, especially in terms of lighter loading protocols
similar to those used in this study. At maximum velocity,
only the 18-kg vest load resulted in a moderate increase in
GRF-z over the baseline condition (8.8%). Similar to the
acceleration phase, a moderate increase in the mean GRF-z
was observed with the 18-kg vest alone (12.4%). It seems that
greater training loads than the traditional recommendation
of 7–15% BM (2,8) may be needed to promote significant
increases in GRF-z production. However, as previous loading
parameters have been assigned on the basis of minimization of
technical alterations, trainers will need to decide whether the
possibility of compromising technique is an acceptable trade-
off for an increased GRF-z training stimulus.
The fact that peak GRF-z did not increase during the
acceleration phase highlights an interesting phenomenon
whereby the addition of mass to the subject does not result
in a corresponding increase in GRF-z. It would be expected
that an increase in peak GRF-z would be similar to the mass
added with each vest load (i.e., 88.3–176.6 N); however, this
was not the case. It seems that additional mass may not
provide as great a GRF-z training stimulus as initially
thought, and other training methods need to be explored
to overload GRF-z production capabilities, especially during
acceleration. This phenomenon is most likely explained by
the additional vertical loading affecting the rise and fall of the
center of mass (COM) during the flight phase, i.e., significant
reduction in flight phase time. If the flight height of the
COM is reduced, then there will be a concomitant reduction
in the GRF-z. It would seem that this reduction in flight time
(rise and fall of COM) counters the effect of the additional
mass. Similar findings have been reported during running at
submaximum velocities while subjects carried compliant poles
(18). Kram (17) found that an additional load of 19% body
Vest Sprinting Kinetics and Kinematics
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weight only increased peak GRF-z by 4.7% and reduced flight
times by 35%. Future research quantifying the path of the
COM is needed to validate this contention.
Vest loading did not result in any significant effects on
horizontal force output during either the maximum velocity
or acceleration phases. Cronin et al. (8) reported a decrease
in forward trunk lean with vest sprinting, likely illustrating
a reduction in the subjects’ ability to control the added mass
added to their frame. Because forward lean has been reported
as a mechanical determinant of horizontal force production
(18,23), it is likely that vest loading affected the subjects’ ability
to produce force in a horizontal direction through a limitation
in their ability to effectively control the added mass and resul-
tant forces.
The addition of vest loading did not result in any
significant effects on power output during the acceleration
phase. Only during the maximum velocity phase did the
18-kg vest condition result in a small decrease in power
compared with the baseline condition (214.3%). Bosco et al.
(3) highlighted the possibility for increases in vertical power
from vest weighted training; however, the results of this
study certainly do not support such a contention. This dis-
sonance can be explained by the different power calculations
in both studies; the power output for the NMT is calculated
as the product of horizontal force and velocity. Because hor-
izontal force production was unaffected and velocity reduced
by vest loading, it is unlikely that vest loading would provide
a horizontal power stimulus. It could be speculated that the
same would be true of the value of vest loading as a vertical
power-training stimulus—that is, given the nonsignificant
changes in GRF-z production and the decrement in velocity
with additional load, it is unlikely that vest loading would
overload vertical power to any great extent. Therefore, if
there is a strong relationship between power production
and sprint performance, as some researchers have alluded
to (11), then careful consideration needs to be given to the
selection of training modalities that maximize horizontal and
vertical power output.
There are several limitations in this study that should be
noted. First, the athlete sample represents a collection of team,
individual and casual sport athletes of varying abilities. Second,
because the loads chosen in this study were absolute, the
loading protocols chosen represented a different percentage of
BM for each participant. In a practical sense, this may not be
possible or probable in an application to the field—hence why
absolute loading was chosen in this study—however future
studies should either select a sample with similar character-
istics (i.e., a team of rugby union forwards), or calculate loads
based on a percentage of each subject mass. Third, although
the Woodway treadmill offers a more realistic running experi-
ence to standard motorized treadmills, particularly for maximal
sprinting, it differs to over-ground running. Maximum sprint
performances are typically 25–30% slower on the Woodway
NMT. Maximum velocity has however been shown to be valid
in comparison with over-ground sprinting (12). Fourth, vertical
and horizontal force data on the treadmill were not collected
from the same location. This could be addressed in future
studies with tri-axial force-plates imbedded beneath the
track (25). Finally, mechanisms for the findings were not
investigated because maximum sprint velocity significantly
decreased with each load. A more detailed analysis could be
conducted in the future if sprint velocity were maintained
with increasing vest loading.
PRACTICAL APPLICATIONS
A fundamental tenet of strength and conditioning practice is
matching the training stimulus to the individual needs of the
athlete, which in turn should produce the desired adaptation.
Important in such an approach is understanding the
mechanical stimuli certain training methods provide. In
terms of vest loading, it is thought that this type of training
provides a means of improving the vertical eccentric/
concentric force capability of athletes during cyclic activities
such as hopping, bounding, and running. It would seem,
however, that the interaction between load and the use of
this training method in producing the desired adaptation
may be more complicated than initially thought. Increasing
vest loading using the loading parameters of this study had
little effect on GRF-z. It would also seem that the vest loads
offered little as a horizontal and vertical power-training
stimulus. Given these findings, careful consideration needs to
be given to the choice of load and utilization of this type of
training if increasing GRF-z production of the athlete is
a training goal. It may be that heavier vest loads than initially
thought are needed to overload cyclic vertical strength and
power, but the effect of such loading on sprint kinematics/
technique needs investigation.
In summary, vest loading may have a place in the preparation
of the athlete, however, understanding when and for what
reason it should occur in the athlete plan is fundamental to
targeted individualized programming. Furthermore, as maxi-
mal effort sprinting is a complex interplay between a number
of different variables, the reader needs to be cognizant that the
optimal training solution for sprinting performance is not
a single modality, but a combination of several. Identifying
individual needs and matching these with modalities that
address the individual’s mechanical/physiological limitations
would seem fundamental in improving strength and condi-
tioning practice and optimizing sprint performance.
ACKNOWLEDGMENTS
The authors wish to thank the committed group of subjects
for their participation in this study. This project did not
receive external financial assistance, and none of the authors
hold any conflict of interest.
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