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Purpose: The effects of different loads on kinematic and kinetic variables during sled towing were investigated with the aim to identify the optimal overload for this specific sprint training. Methods: Thirteen male sprinters (100m PB: 10.91±0.14 s) performed 5 maximal trials over a 20m distance in the following conditions: unloaded (UL) and with loads from +15% to +40% of the athlete's body mass (BM). In these calculations the sled mass and friction were taken into account. Contact and flight times (CT, FT), step length (SL), horizontal hip velocity (vh) and relative angles of hip, knee and ankle (at touch-down and take-off) were measured step-by-step. In addition, the horizontal force (Fh) and power (Ph) and the maximal force (Fh0) and power (Ph0) were calculated. Results: vh, FT and SL decreased while CT increased with increasing load (P < .001). These variables changed significantly also as a function of the step number (P < .01) except between the two last steps. No differences were observed in Fh among loads but Fh was larger in sled towing compared to UL. Ph was unaffected by load up +20%BM but decreased with larger loads. Fh0 and Ph0 were achieved at +20%BM. Up to +20%BM no significant effects on joint angles were observed at touch-down and take-off, while at loads >+30%BM joint angles tend to decrease. Conclusions: The +20%BM condition represents the optimal overload for peak power production: at this load sprinters reach their highest power without significant changes in their running technique (e.g. joint angles).
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Note. This article will be published in a forthcoming issue of the
International Journal of Sports Physiology and Performance. The
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Section: Original Investigation
Article Title: Sled Towing: The Optimal Overload for Peak Power Production
Authors: Andrea Monte, Francesca Nardello, and Paola Zamparo
Affiliations: Department of Neuroscience, Biomedicine and Movement Sciences, University
of Verona, Verona, Italy.
Journal: International Journal of Sports Physiology and Performance
Acceptance Date: November 30, 2016
©2016 Human Kinetics, Inc.
DOI: http://dx.doi.org/10.1123/ijspp.2016-0602
Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Sled towing: the optimal overload for peak power production
Andrea Monte*1, Francesca Nardello1, Paola Zamparo1
Original Investigation
1Department of Neuroscience, Biomedicine and Movement Sciences,
University of Verona, Verona, Italy
Running head: Sled towing: the optimal overload for training
Word count (manuscript): 3485
Word count (abstract): 249
3 Figures
2 Tables
*Corresponding author
Andrea Monte
Address: Department of Neuroscience, Biomedicine and Movement Sciences,
University of Verona. Via Felice Casorati, 43; 37131 - VERONA (ITALY)
Phone number: +39-3395306766
Fax number: +39-045-8425131
E-mail: andrea.monte92@hotmail.com
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Abstract
Purpose: The effects of different loads on kinematic and kinetic variables during sled towing
were investigated with the aim to identify the optimal overload for this specific sprint
training. Methods: Thirteen male sprinters (100m PB: 10.91±0.14 s) performed 5 maximal
trials over a 20m distance in the following conditions: unloaded (UL) and with loads from
+15% to +40% of the athlete’s body mass (BM). In these calculations the sled mass and
friction were taken into account. Contact and flight times (CT, FT), step length (SL),
horizontal hip velocity (vh) and relative angles of hip, knee and ankle (at touch-down and
take-off) were measured step-by-step. In addition, the horizontal force (Fh) and power (Ph)
and the maximal force (Fh0) and power (Ph0) were calculated. Results: vh, FT and SL
decreased while CT increased with increasing load (P < .001). These variables changed
significantly also as a function of the step number (P < .01) except between the two last steps.
No differences were observed in Fh among loads but Fh was larger in sled towing compared
to UL. Ph was unaffected by load up +20%BM but decreased with larger loads. Fh0 and Ph0
were achieved at +20%BM. Up to +20%BM no significant effects on joint angles were
observed at touch-down and take-off, while at loads >+30%BM joint angles tend to decrease.
Conclusion: The +20%BM condition represents the optimal overload for peak power
production: at this load sprinters reach their highest power without significant changes in
their running technique (e.g. joint angles).
Keywords: Sprint running · Load · Coefficient of friction · Force-Velocity relationship
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Nomenclature
STS = Sled Towing Sprinting
BM = Body Mass (kg)
BCoM = Body Centre of Mass
CT = Contact Time (s)
FT = Flight Time (s)
SL = Stride Length (m)
UL = unloaded condition
vh = hip horizontal speed (m·s-1)
Fh = horizontal force (N)
Ph = horizontal Power (W)
vh0 = maximal horizontal velocity (m·s-1)
Fh0 = maximal horizontal force (N)
Ph0 = maximal horizontal power (W)
hipang = hip angle (°)
kneeang = knee angle (°)
ankleang = ankle angle (°)
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Introduction
Sprint running is a fundamental activity in many sports (e.g. athletics, soccer, rugby).
To improve sprint performance programs devoted to increase maximal strength, maximal
power or reactive strength (plyometric exercises) can be proposed.1 As an example, heavy
back squat has been shown to have excellent transfer to sprint performance.2 A positive
transfer of training to sport performance may also be achieved if the conditioning programme
emphasises a similar motor pattern and contraction type according to the training principle of
specificity.1,3,4,5,6 Sled towing sprinting (STS) is a method that is consistent with such
philosophy. Ideally, STS should imitate the range of motion, body position, running
technique and the pattern of muscle activation used in competition.6,7 This training method is
reported to increase: i) the force output demand for the lower limb muscles during contact
time;8 ii) the stride length in the acceleration phase in team sport athletes;4 iii) maximum
velocity.9
From a kinematic point of view, previous studies have mainly focused on parameters
such as step length (SL), contact and flight times (CT, FT) and joint angles. For example,
Alcaraz et al.10 showed a decrease in SL and running velocity with a sled loaded to 16% of
body mass, but no significant changes in running technique (i.e. by analyzing the joint
angles). Moreover, Cronin et al.11, Lockie et al.7 and Maulder et al.12 showed a decrement in
FT and SL, and an increase in CT as a function of sled load.
However, there is no agreement in the literature regarding the exact determination of
the optimal training load and this could be due to the lack of normalization for the coefficient
of friction.13 Indeed, when the applied load is calculated, the sled mass and the coefficient of
friction between sled and ground surface must be taken into account.
Recently, research has also focused on the kinetic parameters of STS.14,15 For
example, Kawamori et al.14 showed differences in ground reactions forces (GRFs) between
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
the conditions without load and with a load equal to 30% of body mass during the third
running step. Cottle et al.16 showed differences in vertical GRF during the starting phase in
the front leg compared to the back one. However, the sled towing effect on force and power
output generated by athletes during a sprint of 20 m is still unknown. Measuring forces for
the entire length of a sprint is quite a difficult task but, recently, Samozino et al.17 have
proposed a method for estimating horizontal force (Fh) during a sprint based on spatio-
temporal parameters. From these data, and from data of hip velocity (vh) it is possible to
calculate the horizontal component of mechanical power output (Ph = Fh.vh). Sled towing is
expected to alter Fh, vh and thus to affect Ph, depending on the applied load.
The aim of this study was to establish which load would maximize mechanical power
(Ph, estimated according to the method of Samozino et al.17) without inducing detrimental
angular changes during sled sprinting with different loads. In this study, to determine the
load, the coefficient of friction was taken into account, as suggested by Linthorne &
Cooper,13. Our hypotheses were: i) sled towing will alter the kinematics and kinetics of sprint
running: but ii) there will be an optimal load that maximizes mechanical power output
without inducing changes in running technique (e.g. in joint angles).
Methods
Participants
Thirteen male sprint athletes participated in this study (see Table 1). To be recruited,
each athlete had at least two years of experience with sled towing training and was free from
any type of injury (this was verified by means of an interview). Moreover, the athletes had to
abstain from training in the 48 hours before the test session. All participants received written
and oral instructions before the study and gave their written informed consent to the
experimental procedure. The experimental protocol was approved by the local Institutional
Review Board.
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Set-up and instrumentation
Kinematic parameters (step length: SL, contact time: CT, flight time: FT, hip
horizontal velocity: vh, hip horizontal acceleration: ah) and relative angles of hip (hipang),
knee (kneeang) and ankle (ankleang) were recorded at each step. To record these data two video
cameras (Elixim Casio, 100 Hz), positioned 18 m from the sprinting direction were interlaced
and synchronized (Figure 1).
The sled had a mass of 8 kg: it was connected to the athletes by means of a 3 m long
rope and a hip belt. Loads could be added on the sled with increments of 0.5 kg.
Experimental Procedure
All sprint tests were conducted in an indoor gym at 20°C and 60% of humidity. A
standardized 20-min warm-up (i.e. running, specific gaits and dynamic stretching) was
undertaken by each participant; it was followed by an initial familiarization to the
instrumentation set-up consisting in 2-3 submaximal sprints with the sledge. Each athlete was
then asked to perform 5 maximal trials over the 20 m distance. All sprint conditions were
randomized; at least 8 min of recovery were observed between trials. In the unloaded trial
(UL) the subjects ran, at their maximal speed, without the sled. In the loaded conditions they
were requested to run, as fast as possible, with an additional mass on the sled corresponding
to +15, +20, +30 and +40% of the athlete’s body mass; to calculate these values the sled mass
as well as the friction force were taken into account (see below).
Friction coefficient
The coefficient of friction () between the PVC floor and the sled was calculated by
means of a load cell (System Pese srl, Magenta (MI), Italy; model: S1, capacity: 50 kg,
accuracy 2 ± 0.1% mV·V-1). To determine we used the “friction sled” method proposed by
Linthorne & Cooper13.
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
The sled was moved over the PVC surface at three different speeds in two conditions:
without load and with an added mass of 20 kg. The static coefficient of friction was on
average of 0.20 ± 0.01. Since friction force is given by the product of vertical (normal) force
times the coefficient of friction this “additional force” corresponds to 20% of the total weight
of the load + sled. For a 70 kg sprinter in the +20%BM condition the applied mass should be
of 14 kg; this mass should be diminished by 20% to take into account friction. Since the sled
mass is 8 kg the mass applied on the sled would be: 14 (14 · 0.2) - 8 = 3.2 kg.
The angle of the rope with the horizontal was calculated for all sprinters, in all
conditions and for all steps at touch down and take off and found to be of 18 ± 1.2°, on the
average. The vertical force component can thus be neglected since the horizontal component
is 95% of the resultant force.
Data analysis
CT, FT, SL, vh, ah, hipang, kneeang, ankleang were recorded step-by-step. Data were
analyzed with SIMI Motion (version 16.1).
The net horizontal antero-posterior force (Fh) applied to BCoM and the corresponding
horizontal mechanical power (Ph) were modeled according to Samozino et al.17:
)()()( tFaerotahmtFh
1)
vhFhPh
2)
where vh and ah are the horizontal hip velocity and acceleration and m is the total mass (e.g.
subject’s mass + overload). The assumption made in this study was that the overload is
applied to BCoM (as implicitly assumed in other studies on this topic: Winwood et al.,18;
Kawamori et al.4; Valencia et al.15). Faero is the aerodynamic resistance and was calculated
as described in detail by Samozino et al17 based on measures of body mass and stature, vh
and air density.
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
The individual force-speed relationships were determined according to Rabita et al.19
and were extrapolated to obtain maximal velocity (vh0) and maximal force (Fh0), as the
intercepts of the force-speed curve with the force and velocity axis, respectively. Ph0 was
calculated according to Samozino et al.20 as follows:
400
0vhFh
Ph
3)
All parameters, were computed step-by-step from the first complete step (the second)
to the last; indeed, contact times can not be calculated in the first step because of the need to
respect the starting line.19,21
Statistical Analysis
Average values and standard deviations were calculated for all variables. A repeated-
measure ANOVA (4 steps and 5 load conditions) was used to determine whether there was a
significant interaction between dependent variables under the various resisted conditions (i.e.
loads) or steps. When a significant main effect (P < .05) was found, a post-hoc test
(Bonferroni pairwise comparison) was conducted to determine where these differences lay.
All statistical analyses were computed using SPSS (Version 20.0).
Results
The mean values and corresponding standard deviations of the kinematic and kinetic
parameters are reported in Table 2 for all the investigated loads. The values of vh0, Fh0 and
Ph0 are reported in Figure 2. The angular parameters at touch-down and take-off are reported
in Figure 3. All subjects completed 13-14 steps: of these the first, the fifth, the tenth and the
last were analyzed.
On the average, all steps, all spatio-temporal parameters changed significantly with
external load (CT, FT, SL and vh: main effect, P < .01). From UL to +40%BM, velocity
decreased by 20.2%, CT increased by 19.0%, FT and SL decreased by 19.3 and 14.8%,
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
respectively. The differences between loads were significant (post hoc tests: P < .001) in all
parameters but for CT and FT (no significant differences were found between +15%BM and
UL).
On the average, all loads, all spatio-temporal variables changed when step number
increased (main effect: P < .01). CT decreased in all load conditions (-40% from the first to
the last step), whereas FT, SL and vh increased (+50.0, +75.8, +113.3% from the first to the
last step, respectively). The post hoc tests revealed no differences between the tenth step and
the last in all variables.
On the average, all steps, all kinetic variables changed significantly with external load
(main effect: P < .01). Ph decreased by 14.9% while Fh increased by 3.7% (from UL to
+40%BM). The changes in Fh were mainly due to differences between UL and the loaded
conditions; as indicated by the post hoc tests no differences in Fh were observed between
+15, +20, +30 and +40%BM.
On the average, all loads, all kinetic variables changed significantly with step number
(main effect: P < .01). Fh and Ph decreased by 82.0 and 62.5%, respectively, from the first to
the last step. The post hoc tests indicate significant differences between steps (P < .001) in all
parameters except for the fifth step compared to the tenth in Fh, and the tenth compared to the
last in Fh.
Finally, vh0, Fh0 and Ph0 were found to depend on the external load: vh0 linearly
decreased with it (vh0 = -0.59 load + 10.83, R2 = 0.99) where Fh0 and Ph0 were achieved at
+20%BM. Post hoc tests revealed no differences between +30 and +40%BM for Fh0 and Ph0
and between +15 and +30 or +40% for Fh0 (see Figure 2). Furthermore, a decrease in Ph0
was observed in the +40%BM condition compared to UL (P = 0.03). Because vh0, Fh0 and
Ph0 were extrapolated from the force-velocity relationship, they could not be expressed step-
by-step.
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
On the average, all steps, angular parameters changed significantly both at touch-
down and take-off when the load increased (main effect: hipang and kneeang: P < .001;
ankleang: P < .05). At touch-down, hipang decreased by 21.2%, ankleang decreased by 5.5% and
kneeang decreased by 7.9% from UL to +40%BM. At take-off, hipang decreased by 9.6% and
kneeang by 9.9% from UL to +40%BM; no differences in ankleang were observed in this phase.
Post hoc tests indicate that, during touch-down and take-off, no significant changes occur
when comparing UL with the +15 and +20%BM conditions (for all angles) nor between +30
and +40%BM (for all angles) (see Figure 3).
On the average, all loads, angular parameters showed significant differences as a
function of the step number both at take-off and touch-down (main effect: P < 0.01); hipang,
kneeang, ankleang all increased when step number increased in all load conditions. Post hoc
tests revealed no differences for kneeang between the 5th and the 10th step compared to the last
during take-off. Furthermore, no differences were observed for ankleang at the 10th step
compared to the last in both running phases.
Discussion
To our knowledge, this is the first study that analyzes kinematic, kinetic and angular
parameters during STS, over a distance of 20m. Moreover, in this study the effect of friction
in the calculation of the external load was taken into account. The main results of this study
indicate that STS affects all sprint parameters during the acceleration phase: indeed,
significant differences do exist at different loads on both spatio-temporal parameters and
lower limb angles. The main finding of this study, however, is that maximal horizontal power
(Ph0) in male sprint athletes reaches its maximal value at +20%BM and that, up to this load,
no significant changes are observed in the angular parameters (e.g. in running technique).
Further studies are needed to understand whether training at the optimal overload for
peak power production is related to longitudinal improvements in sprint performance. In the
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
following parameters the results reported in this study will be discussed and compared with
those reported in the literature
Load determination and coefficient of friction
There are three methods that can be utilized to determine sled load: based on its effect
on sprinting speed, based on a percentage of 1RM or % body mass.1 The latter method was
utilized in this study because it is simpler and easily reproducible. The major criticism to this
method is that a given load would translate in different resistive forces when sprinting over
different surfaces because of differences in the coefficient of friction. This “confounding
factor” was taking in to account in this study.
The static coefficient of friction () measured in our experimental conditions was of
0.20 ± 0.01. This value is comparable to that reported by Linthorne & Cooper,13 for a sled
towed on artificial grass (0.21 ± 0.01). According to these authors can be as large as 0.58 ±
0.01 on a less smooth surface (e.g. on an athletic track). This implies that, when training on
different surfaces, the coefficient of friction could dramatically change and this could have a
strong effect on the calculations of the applied load. For these reasons the different results
reported in the literature so far regarding the optimal load in STS could be attributed to
differences in surface friction.
Kinematic data
Regarding the kinematic parameters, an increase in load during sled towing was
reported to decrease sprint velocity, to increase CT and decrease FT, SL and v.10,12 The
decrease in FT was associated with a decrease in SL: the athlete would spend less time in the
air with shortened strides.7 This increase in CT seems necessary to allow more time to
produce muscular power, in order to overcome the higher resistance.1 Furthermore, a larger
CT could mean more time for the sprinters to orient their resultant force vector more forward.
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
The ability to maximize the anteroposterior impulse plays an important role in sprint
acceleration performance.21,22
In agreement with other studies, we found a decrease in CT and a significant
increment in FT, in SL and in hip velocity as a function of the step number.23 Longer step
lengths are indicative of higher strength and power in the leg muscles: this is peculiar of the
sprinting step.24 Furthermore, shorter contact times were related to faster speeds during
maximum velocity and acceleration phases.25,26 FT is a function of SL: when the step length
is larger, the time of flight increases. However, during the initial steps, the higher CT is
useful to increase the horizontal force production, while the small SL could increase the step
frequency and improve the acceleration of BCoM.24,27
Kinetic data
This study is the first that report data of Fh, Ph, vh0, Fh0 and Ph0 during sled towing
running over a distance of 20m. Indeed, previous studies measured kinetic parameters in the
first steps only.4,15,18
Our results indicate that, although Fh increased in STS compared to the UL condition,
no changes are observed when comparing different loads. This is interesting especially
because many studies have shown that STS may provide a stimulus for increasing muscle
strength, peak force or rate of force development.15,16 The lack of significant differences in Fh
among different loads suggests that the load effectin STS does not depend on how heavy
the load is but only on its presence (at least in the range of loads considered in this study).
No significant differences were observed in Ph at loads of +15 and +20%BM
compared to the unloaded condition, while Ph was lower than in UL at loads > +30%BM.
This decrease should be attributed to the steady decrease in running velocity (vh) and seems
to be attenuated by the lack of differences in Fh while running loaded.
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
In agreement with other studies, we found a significant decrease in Fh and Ph as a
function of step number.17 This could be explained by the lower number of steps in the
ascending part of the Fh vs. vh relationship inherent to the high acceleration capability of
sprinters: they produce their maximal power immediately after the initial steps.19 The higher
Ph during the initial steps is useful to increase SL without reducing step frequency. In fact,
the acceleration capability is, afterwards, quasi-exclusively related with the increase in step
length.23 All these results suggest that the ability to generate high Fh and Ph during the initial
steps is essential to improve sprint acceleration.
Finally, our results indicate that maximal velocity, vh0, decreased linearly as a
function of the load, as previously found by Alcaraz et al.6 while maximal force, Fh0, and
power, Ph0, were achieved +20%BM which is, therefore, the optimal overload for
maximizing horizontal power. Data of vh0, Fh0 and Ph0 reported in this study in the unload
condition are in line with data reported in the literature on trained male sprinters.17,19
Angular parameters
Many studies reported angular data during STS. We found significant increases in all
angles at touch-down and take-off when the load increased. During both phases, loads
corresponding to +15 and +20%BM had no significant effects on all angles, while at +30 and
40% BM all angles decreased. This finding is consistent with previous studies were similar
trends of decreasing trunk angle were observed when increasing sled load.7,28 A larger trunk
lean during sled towing is specific to sprint acceleration movements.11 Therefore, sled towing
may be effective in improving sprint acceleration ability.
A significant alteration in the angular parameters affects negatively running technique
and the consequent positive transfer on training. Because of the reduction in kneeang and
ankleang, there were greater knee and plantar flexions at touch-down and take-off. This
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
suggests that propulsive forces be greater and applied for a longer time during the stance
phase.
Cronin et al.29 suggested that during the stance phase of running, the most significant
braking forces are associated with eccentric contraction of the knee extensors and ankle
plantar flexors. In the current study, at +30 and +40%BM kneeang decreased: consequently,
the breaking phase increased. Hence, these loads may have a negative impact on performance
and they impair a positive transfer on training.
As expected, all angular parameters increased with the running steps, in accordance
with other studies. Cronin et al.29 showed an increase of trunk and knee angle in the first
running steps when the load is applied; in these same conditions Lockie et al.7 found
significant differences at knee angle between the first and the second step. This closer” body
position during the initial steps could be more efficient for acceleration purposes and could
allow a greater application of horizontal force to the ground. It must also be recognized that
such position could reduce flight time and thus lead to a shortened stride.
Practical Applications
In our experimental conditions the +20%BM conditions constitutes the optimal load
for peak power production. As pointed out in this study, however, training loads in sled
towing must be calculated by taking into account friction forces since these change on
different surfaces. Differences in the results reported in different studies (e.g. in the %BM at
which significant kinematic changes occur) can indeed be explained, among the others, by
this factor.
Conclusion
In the present study we show how STS affects kinematic, kinetic and angular
parameters during the acceleration phase of a 20 m sprint, as a function of the load and of the
running step. Horizontal power output is an important determinant for sprinting ability and
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Sled Towing: The Optimal Overload for Peak Power Production” by Monte A, Nardello F, Zamparo P
International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
present data show that this parameter is maximal in the +20%BM condition. In addition, no
changes in joint angles were observed up to this load, indicating that this load is not
detrimental for running technique.
Acknowledgments
We would like to thank Lorenzo Manca and Matteo Saoncella for their help in data
collection.
Conflict of Interest
The authors report no conflict of interest.
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International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
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Figure 1: Schematic drawing of the sled towing track configuration.
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International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Figure 2: Maximal horizontal velocity (vh0), maximal horizontal force (Fh0) and maximal
horizontal power (Ph0) as a function of the load (UL, unload and with loads corresponding to
15, 20, 30 and 40% of the sprinter’s body mass).
* Significant difference between unload and BM% condition (P < .05)
** Significant difference between unload and BM% condition (P < .01)
*** Significant difference between unload and BM% condition (P < .001)
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Figure 3: Relative angles of hip (i.e. the internal angle between trunk and thigh), knee (i.e.
the internal angle between thigh and shank) and ankle (i.e. the internal angle between shank
and foot) during touch-down and take-off as a function of the load (UL, unload and with
loads corresponding to 15, 20, 30 and 40% of the sprinter’s body mass) and the step number
(from the first to the last).
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International Journal of Sports Physiology and Performance
© 2016 Human Kinetics, Inc.
Table 1: Anthropometric characteristics of the sprinters. Data are means ± SD.
Range
Age (years)
19.4±2.3
18-23
Body Mass (kg)
71.5±2.9
68.5-74.5
Body Height (m)
1.77±0.03
1.73-1.85
100 m Personal Best (s)
Number of workouts/week
10.91±0.14
4.46±0.88
10.66-11.11
3.0-6.0
Sled towing Experience (years)
3.77±1.36
2.0-7.0
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Table 2: Kinematic and kinetic data as a function of the imposed load (UL: unloaded; with
loads corresponding to +15, +20, +30 and +40% of BM) in the first, fifth, tenth and last step.
Data are means ± SD.
CT (s)
FT (s)
First
Fifth
Tenth
Last
First
Fifth
Tenth
Last
UL
0.18±0.0
1
0.13±0.0
1
0.11±0.0
1
0.11±0.0
1
0.09±0.0
1
0.11±0.0
1
0.12±0.0
2
0.12±0.0
1
+15
%
0.19±0.0
2
0.13±0.0
1
0.12±0.0
1
0.12±0.0
1
0.09±0.0
2
0.11±0.0
1
0.12±0.0
1
0.11±0.0
1
+20
%
0.19±0.0
2
0.14±0.0
1
0.12±0.0
1
0.12±0.0
1
0.08±0.0
1
0.10±0.0
1
0.11±0.0
1
0.12±0.0
1
+30
%
0.20±0.0
3
0.15±0.0
1
0.13±0.0
1
0.13±0.0
1
0.08±0.0
2
0.09±0.0
1
0.10±0.0
1
0.10±0.0
1
+40
%
0.21±0.0
2
0.16±0.0
1
0.15±0.0
1
0.13±0.0
1
0.07±0.0
2
0.09±0.0
1
0.09±0.0
1
0.09±0.0
1
SL (m)
vh (ms-1)
First
Fifth
Tenth
Last
First
Fifth
Tenth
Last
UL
1.00±0.0
3
1.58±0.0
6
1.89±0.0
7
1.85±0.0
4
3.74±0.2
0
6.70±0.5
4
8.04±0.4
9
8.04±0.3
6
+15
%
0.97±0.0
4
1.52±0.0
9
1.78±0.1
4
1.69±0.0
6
3.54±0.4
2
6.35±0.4
4
7.55±0.5
6
7.36±0.4
1
+20
%
0.96±0.0
4
1.48±0.0
8
1.70±0.0
9
1.65±0.1
0
3.51±0.3
2
6.12±0.4
0
7.34±0.5
6
7.03±0.6
3
+30
%
0.92±0.0
4
1.35±0.0
8
1.59±0.0
9
1.62±0.1
1
3.34±0.3
2
5.54±0.5
0
6.78±0.5
0
6.97±0.4
8
+40
%
0.89±0.0
4
1.30±0.0
7
1.54±0.1
1
1.53±0.1
2
3.21±0.2
6
5.34±0.3
4
6.49±0.6
2
6.93±0.1
0
Ph (W)
Fh (N)
First
Fifth
Tenth
Last
First
Fifth
Tenth
Last
UL
1800±316
1327±313
1054±194
732±132
479±63
196±32
130±17
91±8
+15%
1863±616
1338±289
1044±218
764±144
514±117
209±31
137±19
103±14
+20%
1879±573
1269±272
1010±231
600±121
528±105
206±31
136±22
85±9
+30%
1836±608
1120±280
915±191
715±138
541±117
200±31
134±19
102±13
+40%
1788±393
1108±222
900±253
624±100
552±83
206±29
137±25
90±6
Footnote: CT: contact time; FT: flight time; SL: step length; vh: horizontal speed; Ph; horizontal power; Fh:
horizontal force.
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... One of the most commenly used resisted sprint methods is weighted sled training (consisting of a sled device attached to the athlete by a chest or waist harness). This methodology requires greater demand for horizontal forces evoked by the mass of a weighted sled together with the resulting friction between the sled and the ground surface. 1 Some of the mechanisms by which this training method induces improvements in sprint performance are related to an increase in (1) the horizontal force production during each ground contact, 2 (2) the stride length in the acceleration phase, 3 and (3) the maximal velocity. 4 In a recent review, Alcaraz et al 5 suggested that resisted sprint training is an effective method for the development of sprint performance, mainly in the early acceleration phase (≤10 m), with little impact in the maximum velocity phase (≥20 m). ...
... 5,20 An external load about 10% to 12.5% of body mass (BM), which induces about 10% of decrement in unloaded velocity while allowing to maintain the sprint technique, has been typically recommended. 2,[21][22][23] However, more recently, it has been suggested that heavier loads (≈80% BM) should be used to improve sprinting acceleration, as they allow athletes to produce greater horizontal force in a forward-oriented body position throughout the sprint. 24,25 Morin et al 25 tested the use of very heavy sled load (80% BM) in soccer players and observed a substantial, increased horizontal force production compared with nonresisted sprinting. ...
... Most of the studies analyzing the acute effects of using different sled loads have focused on kinematic and kinetic variables such as stride length, stride frequency, flight times, contact times, joint angles, force, rate of force development, and power production. 1,2,5,22,[27][28][29] However, to the best of our knowledge, the metabolic and physical response to different loading conditions during resisted sprint training has not been previously analyzed. A better understanding of the physical fitness and metabolic acute and short-term responses to a wide range of loading conditions during resisted sprint training may help to improve the sprint training process and recovery strategies. ...
Article
Purpose: To analyze the acute and short-term physical and metabolic responses to resisted sprint training with 5 different loading conditions (0%, 20%, 40%, 60%, and 80% body mass). Methods: Fifteen male participants performed 8 × 20-m sprints with 2-minute rests between sprints with 5 different loading conditions. Subjects performed a battery of tests (creatine kinase and lactate concentrations, countermovement jump, 20-m sprint, and isokinetic knee extension and flexion contractions) at 3 different time points (preexercise [PRE], postexercise [POST], and 24-h postexercise [POST24H]). Results: Results revealed significant increases in blood lactate for all loading conditions; however, as sled loadings increased, higher blood lactate concentrations and increments in sprint times during the training session were observed. Significant increases in creatine kinase concentration were observed from PRE to POST24H for all loading conditions. Concerning physical performance, significant decreases in countermovement-jump height from PRE to POST were found for all loading conditions. In addition, significant decreases in 20-m sprint performance from PRE to POST were observed for 0% (P = .05) and 80% (P = .02). No significant differences with PRE were observed for the physical-performance variables at POST24H, except for 20% load, which induced a significant decrease in mean power during knee flexion (P = .03). Conclusions: These results suggest that the higher the load used during resisted sprint training, the higher the physical-performance impairments and metabolic response produced, although all loading conditions led to a complete recovery of sprint performance at POST24H.
... Additionally, it was shown that sled towing increased trunk forward lean angle while weighted vest decreased it [12]. Effects on ME were also assessed during sled towing [13,14], while no information concerning weighted vests is present. The type of resistance and its application point appear to be crucial in determining the position of the segments of the body during the acceleration phase [11]. ...
... The type of resistance and its application point appear to be crucial in determining the position of the segments of the body during the acceleration phase [11]. Sleds are usually towed by athletes with a belt insisting on the hips [13] and more rarely using a shoulder vest harness [15]. While both hip and shoulder attachments lead to similar alterations in GRF compared to unresisted sprinting, they differ regarding knee joint kinematics, with the shoulder attachment displaying larger knee flexion [15]. ...
... Times to cover all distances increased in both BB2.5 and BB5 conditions over BW condition. These findings are consistent with other studies involving sprinting with increasing overloads [13,32,33]. In these studies, sprinters performed sled towing and, as the overload increased, the time to cover 20 and 30 m distances underwent a significant deterioration [13,32]. ...
Article
Full-text available
Background: Effective sprinting requires large acceleration capabilities. To accelerate, large amount of force must be produced and applied effectively. The use of different implements such as sleds and vests can increase the amount of force produced and alter sprinting effectiveness. We propose the use of increasing overload via the Bulgarian Bag (BB) as a means to modify athletes' sprint and acutely increase force and power production. Methods: 24 young athletes performed three sprints over 20 m in three different conditions: unloaded (BW) and loaded with BB weighing 2.5% (BB2.5) and 5% (BB5) of the athlete's body mass. Sprint times at 2.5, 5, 10, 15, and 20 m were acquired and used to compute the force-velocity relationship for the sprints. Maximal velocity (V0), peak force (F0), peak power (PP), and decrease in ratio of force (DRF) were computed. Results: the additional load caused a decrease in sprint times (p < 0.05) and V0 (p = 0.028), conversely no differences were found for F0 (p = 0.21), PP (p = 0.50), and DRF (p = 0.83). Conclusions: Based on those findings, BB can be an alternative method to effectively overload sprint training toward improving sprinting performance.
... Despite the popularity of sled towing, there is a lack of consensus regarding the optimal loading range (i.e., light or heavy loads) for RST (1,20). In general, an external load of 10-12.5% of body mass (BM), which induces ;10% reduction in maximum (unloaded) velocity with slight changes in sprinting technique has been typically suggested by researchers (3,14,15,22). Nonetheless, there is some evidence that the sled load selection could be velocity-specific-dependent, with heavier loads (.20% BM) being more recommended for improving initial acceleration (characterized by slower velocities and higher resistive forces) and lighter loads (,10% BM) for improving the maximum velocity phase (characterized by higher velocity and lower resistive forces) (20). ...
... Overall, the heavier sled load (32.2% BM) caused greater disruptions to sprint kinematics than those observed with the lighter sled load (12.6% BM) (14). Other authors have also reported progressive alterations in sprint technique (i.e., decreases in fight time and SL, and increases in contact time) as a function of sled loading (6,7,15). However, as aforementioned, recent investigations have recommended that a very heavy sled load (80% BM) may be required to provide the optimal training condition for enhancing horizontal force production (9,17). ...
... The lighter loads used in that study (12.8-25.4% BM) probably explain these relative differences. In line with this hypothesis, Monte et al. (15) observed hip kinematic alterations when using sled loads between 30 and 40% BM, without finding significant differences from loads equal to ;20% BM (in comparison with unloaded conditions). Unfortunately, kinematic comparisons with loads .40% ...
Article
We examined the effects of five loading conditions (0%, 20%, 40%, 60%, and 80% of body-mass [BM]), on resisted sprint performance and kinematics in male rugby players over different distances. Ten players from the Brazilian National Team (20.1±3.3 years; 88.7±18.8 kg; 178.3±6.2 cm) performed 20-m sprints under the five loading conditions. Sprint times in 5-, 10- and 20-m were recorded. Stride length (SL), and hip, knee and ankle angles were measured using an eight-sensor motion analysis system. The kinematic parameters were calculated over the different distances. Heavier loads led to significantly greater velocity loss (P < 0.001-0.05). Significant reductions in SL were also observed when comparing 0% BM and all resisted sprints in all assessed distances (P < 0.001-0.05, Effect Size, [ES]: 1.35-4.99). Very-heavy (80% BM) sled load provoked significantly greater decreases in SL than the rest of loading conditions (P < 0.01-0.05). Important kinematic alterations were observed for all loading conditions and sprint distances when compared to 0%BM (ES: 0.76-1.79, for hip-angle; 0.20-1.40, for knee-angle; and 0.73-1.88, for ankle-angle). Moreover, 80% BM induced significantly higher hip flexion, lower knee flexion and higher ankle dorsiflexion than 20% BM condition at 5-10- and 10-20-m distances (P < 0.05). Lighter sled loads (< 40% BM) seem to be more adequate to improve speed ability without provoking drastic changes in unloaded sprinting technique, whereas heavier loads might be more suitable for optimizing horizontal force production and thus, acceleration performance.
... Hence, a deeper understanding of running mechanics during ST across different loading conditions is of relevance for coaches and practitioners. Decreases in sprint velocity, SL, FT, and SF, an increase in CT, and alterations in joint kinematics have been observed, inducing a tendency to a "Groucho" running pattern when increasing sled loads (9,26,69,81,86). The "Groucho" running pattern is a form of locomotion in which the knees remain flexed during the complete stride. ...
... Regarding the effect of ST on K leg , Zabaloy et al. (126) and Padua et al. (94) showed a decrease in K leg with increasing sled loads. An excessive sled load may require too much amortization time during the stretchshortening cycle (122), because longer CT has been observed with increased sled loads (9,26,69,81,86), thus hampering the exploitation of the stretch-shortening cycle. Indeed, it has been found that heavier sled loads result in greater kinematic alterations in the ankle joint because of higher dorsiflexion at foot strike and increased plantar flexion at toe off (97), which allows athletes to increase their CT, to produce the force required to overcome the excessive overload. ...
Article
Sprinting is a key component for many individual and team sports. Therefore, to enhance sprint performance, various training methods are widely used by coaches and practitioners, including maximum sprint speed and resisted sprint training. Resisted sprinting with sled towing is a method that has recently received considerable attention from the sport science community. However, to date, no consensus exists regarding its acute and chronic effects in team sport athletes. This narrative review aimed to (a) review and analyze the mechanics of sprinting under unresisted and resisted conditions with a specific focus on team sport disciplines; (b) provide a thorough and applied discussion on the importance of considering acute and chronic effects of sled loading on technique, electromyographic activity, and force production, as well as on the role of muscle architecture and neural factors in sled training; (c) analyze the effects of increasing sled loads during acceleration and maximum velocity phases on contact and flight phases, while concomitantly examining kinetic, kinematic, and neuromuscular aspects, because all these factors affect each other and cannot be properly understood in isolation.
... Contact time is crucial in sprinting as it is the only time an athlete has the ability to create force [63]. RSS has been used to help increase the application of muscular force, especially at the hip, knee, and ankle in trained athletes [30,31,64]. Previous research demonstrates [25,30,65] that CT increases with the addition of load in resisted sprints, with increases of 17-22% reported at loads ranging from 12.6-32.2%BM ...
... For example, when squatting at heavier loads research indicates that there is a reduction in movement velocity, increasing the time to produce force, which in turn increases power output at lighter loads [67]. This increase in CT appears consistent across the literature [25,30,42,43,55,64], only a handful of studies have examined the change in CT in unloaded sprinting after an RSS intervention and indicate that this does not appear to transfer to unloaded sprinting [15] and may facilitate a positive adaptation by improving rate of force development (RFD) [38]. ...
Article
Full-text available
In this study, we assessed the acute kinematic effects of different sled load conditions (unloaded and at 10%, 20%, 30% decrement from maximum velocity (Vdec)) in different sporting populations. It is well-known that an athlete’s kinematics change with increasing sled load. However, to our knowledge, the relationship between the different loads in resisted sled sprinting (RSS) and kinematic characteristics is unknown. Thirty-three athletes (sprinters n = 10; team sport athletes n = 23) performed a familiarization session (day 1), and 12 sprints at different loads (day 2) over a distance of 40 m. Sprint time and average velocity were measured. Sagittal-plane high-speed video data was recorded for early acceleration and maximum velocity phase and joint angles computed. Loading introduced significant changes to hip, knee, ankle, and trunk angle for touch-down and toe-off for the acceleration and maximum velocity phase (p < 0.05). Knee, hip, and ankle angles became more flexed with increasing load for all groups and trunk lean increased linearly with increasing loading conditions. The results of this study provide coaches with important information that may influence how RSS is employed as a training tool to improve sprint performance for acceleration and maximal velocity running and that prescription may not change based on sporting population, as there were only minimal differences observed between groups. The trunk lean increase was related to the heavy loads and appeared to prevent athletes to reach mechanics that were truly reflective of maximum velocity sprinting. Lighter loads seem to be more adequate to not provoke changes in maxV kinematics. However, heavy loading extended the distance over which it is possible to train acceleration.
... For example, Cross et al. [38], using a sled towing protocol, found a range from 70-96% BM (recreational athletes: 70%; sprinters: 96%) to be optimal for power production. Opposite to these findings, Monte et al. [39] established maximal horizontal power production in male sprint athletes at 20% BM. In this study, although all kinematic parameters changed significantly with external load (CT, FT and SL), there was no variation in the angular parameters (i.e., in running technique). ...
Article
Full-text available
This study's aim was to analyze muscle activation and kinematics of sled-pushing and resisted-parachute sprinting with three load conditions on an instrumentalized SKILLRUN ® tread-mill. Nine male amateur rugby union players (21.3 ± 4.3 years, 75.8 ± 10.2 kg, 176.6 ± 8.8 cm) performed a sled-push session consisting of three 15-m repetitions at 20%, 55% and 90% body mas and another resisted-parachute session using three different parachute sizes (XS, XL and 3XL). Sprinting kinematics and muscle activity of three lower-limb muscles (biceps femoris (BF), vastus lateralis (VL) and gastrocnemius medialis (GM)) were measured. A repeated-measures analysis of variance (RM-ANOVA) showed that higher loads during the sled-push increased (VL) (p ≤ 0.001) and (GM) (p ≤ 0.001) but not (BF) (p = 0.278) activity. Furthermore, it caused significant changes in sprinting kinematics, stiffness and joint angles. Resisted-parachute sprinting did not change kinematics or muscle activation, despite producing a significant overload (i.e., speed loss). In conclusion, increased sled-push loading caused disruptions in sprinting technique and altered lower-limb muscle activation patterns as opposed to the resisted-parachute. These findings might help practitioners determine the more adequate resisted sprint exercise and load according to the training objective (e.g., power production or speed performance).
... The present study showed that FT and SL decreased with increasing loads, in line with previous studies (27,29). These differences were even more accentuated in the Vmax phase (Table 3). ...
Article
This study aimed to compare muscle activity, leg stiffness, and kinematics (contact and flight time [FT], stride length and frequency, and trunk angle [TA]) of unloaded sprinting to resisted sprint (RST) using different loads. Twelve male rugby players (age: 23.5 ± 5.1 years; height: 1.79 ± 0.04 m; body mass 82.5 ± 13.1 kg) performed 30-m sprints using different loading conditions (0, 10, 30 and 50% of velocity loss-Vloss-from the maximum velocity reached under unloaded condition). Muscle activity from 4 muscles (biceps femoris long head, rectus femoris [RF], gluteus medius and gastrocnemius), leg stiffness (Kleg), and kinematics were measured during the acceleration and maximum velocity (Vmax) phases of each sprint. Heavier loads led to significantly lower biceps femoris long head activation and higher rectus femoris activity (p < 0.01-0.05). Significant reductions in Kleg were observed as loading increased (p < 0.001-0.05). Kinematic variables showed substantial changes with higher loads during the acceleration and Vmax phase. In conclusion, the heavier the sled load, the higher the disruptions in muscle activity, Kleg, and kinematics. When coaches and practitioners intend to conduct resisted sprint training sessions without provoking great disruptions in sprint technique, very-heavy sled loads (greater than 30% Vloss) should be avoided. However, heavy sled loads may allow athletes to keep specific positions of the early acceleration phase for longer time intervals (i.e., first 2-3 strides during unresisted sprints).
... Using a similar load (12.6% body mass), de Hoyo et al. (2016) reported an almost certain increase in countermovement jump and a likely decrease in sprint time (30-50m) in a group of U-19 elite soccer players. A more recent study by Monte and colleagues showed that towing with a load of 20% body mass maximised peak power production in male trained sprinters (100m personal best 10.91 ± 0.14) (Monte, Nardello & Zamparo, 2017). An assisted sprint training study by Upton (2011) showed this type of training method to be superior to resisted sprint training for shorter sprint distance (up to 13.7m) in female collegiate soccer players (Collegiate Division IA). ...
Article
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Sprint performance plays an important role in the success of many sports including track and field and teambased sports. Resisted sprint equipment has shown to be an effective method to increase sprint velocity and acceleration. The aim of the study was to determine the intrasession and intersession (7 days) reliability of a commercially available resisted sprint machine in recreationally trained individuals for two resistance settings. Fourteen recreationally active participants partook in the study (male = 10, female = 4) over a 7-day period. Three maximal 15m sprints, at two resistance levels (R0 and R5), were undertaken in a randomised order (6 sprints in total at each trial). Intrasession (comparison of the first 3 sprints for each trial) and intersession (mean of the 3 sprints for both trials) correlation coefficient (ICC), coefficients of variation (%CV), average variability, SEM and minimal detectable difference were calculated for 5 and 15m for both resistance levels. Intrasession reliability was very large to nearly perfect across both distances and resistance levels (ICC range 0.79-0.98), %CV ranged between 2.4-5.8% with larger values seen during the first trial for three of the four indices. Intersession reliability was very large to nearly perfect across all variables (ICC range 0.87-0.97), %CV was small and ranged between 2.0-4.1%. Average variability was small for all measurements. The Run RocketTM showed high intra and intersession reliability. The results show that this equipment could be reliably used within a sprint programme for recreationally trained individuals. Keywords: Athletic training; Sports performance; Exercise training.
... In spite of the lack of significant differences between training groups, meaningful differences between RST and CG were observed for the 5 m sprint change. These results are in line with previous research reporting that RST (i.e., using sled towing and weighted vests) was effective in improving kinetics and kinematics during short bouts of accelerations (Alcaraz et al., 2018;Monte et al., 2017). A reason for this difference between groups could be related to the greater increase in the capacity to produce anteriorposterior force application during RST. ...
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This study aimed to compare the effects of 6-week resisted sprint (RST) versus conventional (unresisted) sprint training (CG) on sprint time, change of direction (COD) speed, repeated sprint ability (RSA) and jump performance (countermovement jump (CMJ) and standing long jump (SLJ)) in male young tennis players. Twenty players (age: 16.5 ± 0.3 years; body mass: 72.2 ± 5.5 kg; body height: 180.6 ± 4.6 cm) were randomly assigned to one of the two groups: RST (n = 10) and CG (n = 10). The training program was similar for both groups consisting of acceleration and deceleration exercises at short distances (3-4 m), and speed and agility drills. The RST group used weighted vests or elastic cords during the exercises. After 6 weeks of intervention, both training regimes resulted in small-to-moderate improvements in acceleration and sprint ability (5, 10, 20 m), SLJ and CMJ performances, COD pivoting on both, the non-dominant (moderate effect) and the dominant (small effect) foot, and the percentage of decrement (small effects) during a RSA test. Between-group comparisons showed that the SLJ (Δ = 2.0%) and 5 m sprint time (Δ = 1.1%) improved more in the RST group compared with the CG group. This study showed that 6 weeks of RST or unresisted training are time-efficient training regimes for physical improvements in young male tennis players.
Thesis
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En la presente Tesis doctoral se tratarán una serie de problemáticas relacionadas con el entrenamiento de la velocidad de sprint en el rugby. Todas ellas están estrechamente relacionadas entre sí, ya que plantean la necesidad de establecer métodos de entrenamiento y evaluaciones específicas para los jugadores de rugby y en relación con el puesto específico de juego. La Tesis está compuesta por cinco estudios, los cuales fueron realizados con jugadores de rugby de edades infanto-juvenil (12-18 años) y senior (mayores), teniendo como objetivo analizar diferentes aspectos relacionados con el entrenamiento de la velocidad de sprint: (1) investigar el intervalo en el que los jugadores de rugby masculinos alcanzan la velocidad máxima en un sprint de 50-m según la edad y puesto específico, adicionalmente establecer la distancia óptima para la evaluación de la velocidad del sprint y comparar las diferencias en características antropométricas, rendimiento en sprint y momento lineal según la edad y puesto especifico; (2) investigar la relación entre una prueba de fuerza isométrica específica de sprint (SIST) y la velocidad máxima sin carga añadida (Vmáx), los tiempos de sprint en diferentes condiciones de carga respecto del peso corporal (PC) y pérdida de velocidad (Vloss) durante un entrenamiento de sprint resistido con trineos de arrastre (RST) y un conjunto de pruebas de fuerza (dinámica e isométrica) y saltos en jugadores de rugby; (3) analizar las diferencias en el perfil de fuerza-velocidad (Fv) y el rendimiento del sprint, la fuerza y el salto según la posición de juego, y examinar las relaciones entre estos parámetros de condición física dentro de los puestos de juego más específicos en rugby; (4) analizar los efectos en rendimiento de fuerza, el salto y sprint luego de programa de entrenamiento de fuerza (RT) individualizado basado en desequilibrio del perfil fuerza-velocidad (FVimb) en jugadores de rugby; (5) comparar los cambios en la actividad muscular (EMG), stiffness (Kleg) y las variables cinemáticas del sprint sin carga respecto del RST con diferentes cargas según Vloss. Respecto de los resultados aportados por nuestros estudios, y en línea con las conclusiones aportadas consideramos que: i) debemos utilizar una distancia adecuada para evaluar el sprint; ii) usar medios adecuados de evaluación de las capacidades físicas de los jugadores de rugby; iii) individualizar los entrenamientos de los jugadores de rugby, dadas las grandes diferencias que hay entre categorías de edad y entre puestos específicos en este deporte; y finalmente, iv) seleccionar el método y la carga mas adecuada para entrenar la velocidad de sprint en función de los objetivos y la distancia a utilizar en los entrenamientos.
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This study aimed to validate a simple field method for determining force- and power-velocity relationships and mechanical effectiveness of force application during sprint running. The proposed method, based on an inverse dynamic approach applied to the body center of mass, estimates the step-averaged ground reaction forces in runner's sagittal plane of motion during overground sprint acceleration from only anthropometric and spatiotemporal data. Force- and power-velocity relationships, the associated variables, and mechanical effectiveness were determined (a) on nine sprinters using both the proposed method and force plate measurements and (b) on six other sprinters using the proposed method during several consecutive trials to assess the inter-trial reliability. The low bias (<5%) and narrow limits of agreement between both methods for maximal horizontal force (638 ± 84 N), velocity (10.5 ± 0.74 m/s), and power output (1680 ± 280 W); for the slope of the force-velocity relationships; and for the mechanical effectiveness of force application showed high concurrent validity of the proposed method. The low standard errors of measurements between trials (<5%) highlighted the high reliability of the method. These findings support the validity of the proposed simple method, convenient for field use, to determine power, force, velocity properties, and mechanical effectiveness in sprint running. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.