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Ground reaction force across the transition during sprint acceleration

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Ryu Nagahara at National Institute of Fitness and Sports in Kanoya
Ryu Nagahara
Hiroaki Kanehisa
Hiroaki Kanehisa
Hiroaki Kanehisa
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Tetsuo Fukunaga at National Institute of Fitness and Sports in Kanoya
Tetsuo Fukunaga
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Abstract and Figures

Abrupt changes in kinematics during sprint acceleration called transitions have previously been observed. This study aimed to examine whether ground reaction force (GRF) variables during sprint acceleration also show specific features of the transitions. Twenty‐one male sprinters performed 60‐m sprints, during which GRF data were recorded. Step‐to‐step spatiotemporal and GRF variables were approximated using an exponential function and three straight lines. Moreover, statistical parametric mapping (SPM) was used to test changes in GRF curves across the transitions. For running speed, the exponential approximation resulted in smaller root‐mean‐square (RMS) of residuals. For the other variables, however, RMS of residuals were smaller when the three lines approximation was adopted. Breakpoints around the 5th and 15th steps were detected using effective vertical impulse during the braking phase with the three lines approximation. Across the breakpoints, SPM showed significant differences in the anteroposterior GRF curves at the next step after the first breakpoint and at the second breakpoint. Moreover, the second braking phase of the anteroposterior GRF appeared at the next step after the first breakpoint, and the corresponding first propulsive phase disappeared at the second breakpoint. Consequently, changes in GRF variables during sprint acceleration are likely accompanied by specific alterations. The breakpoints around the 5th and 15th steps found in an effective vertical impulse during the braking phase can be a criterion indicating transitions in GRF variables during sprint acceleration. The transitions are characterized by an appearance and disappearance of the second braking and first propulsive phases, respectively, of the anteroposterior GRF.
Example of GRF signals during the entire sprint acceleration of 50‐m sprinting (A) and the definition of the braking and propulsive phases of GRF signals at the 1st, 13th, and 25th steps (B) for a typical participant. (A) The numbers in each panel indicate step numbers from the first step after block clearance. (B) The areas filled with stripe pattern show vertical GRF during braking phases, and the rests of areas show vertical GRF during propulsive phases. The time axes are from the starting signal. The horizontal dotted lines show the body weight of the participant
Example of GRF signals during the entire sprint acceleration of 50‐m sprinting (A) and the definition of the braking and propulsive phases of GRF signals at the 1st, 13th, and 25th steps (B) for a typical participant. (A) The numbers in each panel indicate step numbers from the first step after block clearance. (B) The areas filled with stripe pattern show vertical GRF during braking phases, and the rests of areas show vertical GRF during propulsive phases. The time axes are from the starting signal. The horizontal dotted lines show the body weight of the participant
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Changes in spatiotemporal variables during accelerated sprinting until the 25th step and an exponential and three lines approximations. (A) Running speed, (B) step length, (C) step frequency, (D) running acceleration, (E) support time, (F) flight time, (G) braking time, (H) propulsive time. The value at each step is the mean of all participants. Black lines indicate exponential approximation, while gray lines indicate three lines approximation. Numbers in each panel show root‐mean‐square errors of residuals for the exponential and three lines approximations. Numbers in parentheses in each panel indicate the first and second breakpoint steps
Changes in spatiotemporal variables during accelerated sprinting until the 25th step and an exponential and three lines approximations. (A) Running speed, (B) step length, (C) step frequency, (D) running acceleration, (E) support time, (F) flight time, (G) braking time, (H) propulsive time. The value at each step is the mean of all participants. Black lines indicate exponential approximation, while gray lines indicate three lines approximation. Numbers in each panel show root‐mean‐square errors of residuals for the exponential and three lines approximations. Numbers in parentheses in each panel indicate the first and second breakpoint steps
… 
Changes in ground reaction force variables during accelerated sprinting until the 25th step and an exponential and three lines approximations. (A) Net antero‐posterior impulse, (B) braking impulse, (C) propulsive impulse, (D) net antero‐posterior mean force, (E) braking mean force, (F) propulsive mean force, (G) effective vertical impulse, (H) effective vertical impulse during the braking phase, (I) effective vertical impulse during the propulsive phase, (J) average horizontal external power, (K) effective vertical mean force during the braking phase, (L) effective vertical mean force during the propulsive phase. The value at each step is the mean of all participants. Black lines indicate exponential approximation, while gray lines indicate three lines approximation. Numbers in each panel show root‐mean‐square errors of residuals for the exponential and three lines approximations. Numbers in parentheses in each panel indicate the first and second breakpoint steps
Changes in ground reaction force variables during accelerated sprinting until the 25th step and an exponential and three lines approximations. (A) Net antero‐posterior impulse, (B) braking impulse, (C) propulsive impulse, (D) net antero‐posterior mean force, (E) braking mean force, (F) propulsive mean force, (G) effective vertical impulse, (H) effective vertical impulse during the braking phase, (I) effective vertical impulse during the propulsive phase, (J) average horizontal external power, (K) effective vertical mean force during the braking phase, (L) effective vertical mean force during the propulsive phase. The value at each step is the mean of all participants. Black lines indicate exponential approximation, while gray lines indicate three lines approximation. Numbers in each panel show root‐mean‐square errors of residuals for the exponential and three lines approximations. Numbers in parentheses in each panel indicate the first and second breakpoint steps
… 
Correlation coefficients of effective vertical impulses during the braking (A) and propulsive phases (B) with step length and step frequency. Horizontal dotted lines indicate P = .05
Correlation coefficients of effective vertical impulses during the braking (A) and propulsive phases (B) with step length and step frequency. Horizontal dotted lines indicate P = .05
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Changes in effective vertical impulse during the braking phase for individuals. (A) to (U) indicate participant 1 to 21. Black lines indicate exponential approximation, while gray lines indicate three lines approximation. Numbers in each panel show root‐mean‐square errors of residuals for the exponential and three lines approximations. Numbers in parentheses in each panel indicate the first and second breakpoint steps
+2
Changes in effective vertical impulse during the braking phase for individuals. (A) to (U) indicate participant 1 to 21. Black lines indicate exponential approximation, while gray lines indicate three lines approximation. Numbers in each panel show root‐mean‐square errors of residuals for the exponential and three lines approximations. Numbers in parentheses in each panel indicate the first and second breakpoint steps
… 
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450
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wileyonlinelibrary.com/journal/sms Scand J Med Sci Sports. 2020;30:450–461.
© 2019 John Wiley & Sons A/S.
Published by John Wiley & Sons Ltd
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INTRODUCTION
Unstable speed locomotion is an interesting subject to under-
stand the regulation of locomotor function in association with
changes in locomotion speed. Comparing sprinting during
the initial acceleration with that at maximal speed, force
application and accompanying kinematics are largely differ-
ent owing to specific tasks at the different running speed and
acceleration. Thus, sprinters need to change their running
modality during maximal effort sprint acceleration running
(hereafter, sprint acceleration). Although it can be considered
that the smooth changes in locomotion are reasonable for
Received: 7 June 2019
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Revised: 15 October 2019
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Accepted: 6 November 2019
DOI: 10.1111/sms.13596
ORIGINAL ARTICLE
Ground reaction force across the transition during sprint
acceleration
RyuNagahara
|
HiroakiKanehisa
|
TetsuoFukunaga
This research was conducted at the National Institute of Fitness and Sports
in Kanoya.
National Institute of Fitness and Sports in
Kanoya, Kagoshima, Japan
Correspondence
Ryu Nagahara, National Institute of Fitness
and Sports in Kanoya, 1 Shiromizu-cho,
Kanoya, Kagoshima 891-2393, Japan.
Email: nagahara@nifs-k.ac.jp
Abrupt changes in kinematics during sprint acceleration called transitions have pre-
viously been observed. This study aimed to examine whether ground reaction force
(GRF) variables during sprint acceleration also show specific features of the transi-
tions. Twenty-one male sprinters performed 60-m sprints, during which GRF data
were recorded. Step-to-step spatiotemporal and GRF variables were approximated
using an exponential function and three straight lines. Moreover, statistical paramet-
ric mapping (SPM) was used to test changes in GRF curves across the transitions.
For running speed, the exponential approximation resulted in smaller root-mean-
square (RMS) of residuals. For the other variables, however, RMS of residuals was
smaller when the three lines approximation was adopted. Breakpoints around the
5th and 15th steps were detected using effective vertical impulse during the brak-
ing phase with the three lines approximation. Across the breakpoints, SPM showed
significant differences in the antero-posterior GRF curves at the next step after the
first breakpoint and at the second breakpoint. Moreover, the second braking phase
of the antero-posterior GRF appeared at the next step after the first breakpoint,
and the corresponding first propulsive phase disappeared at the second breakpoint.
Consequently, changes in GRF variables during sprint acceleration are likely accom-
panied by specific alterations. The breakpoints around the 5th and 15th steps found
in an effective vertical impulse during the braking phase can be a criterion indicating
transitions in GRF variables during sprint acceleration. The transitions are character-
ized by an appearance and disappearance of the second braking and first propulsive
phases, respectively, of the antero-posterior GRF.
KEYWORDS
braking, ground reaction force, impulse, propulsion, running speed, statistical parametric mapping
... Sprinting encompasses multiple phases (e.g., start, acceleration and deceleration), with the sprint acceleration phase further divided into initial, middle and later acceleration sections. 11,12 Moreover, kinematic and kinetic characteristics and determinants of sprinting, [13][14][15][16] as well as important strength-power indicators, 17-20 may vary across different sections of sprinting. Thus, there is a need to explore the relationships between RFDs of GRF during the support phase of sprinting and overground sprint performance at multiple sections in sprinting. ...
... The GRF signal was filtered using a Butterworth low-pass digital filter at a cut-off frequency of 50 Hz. 12,15 Using the filtered GRF data, foot strike and toe-off instants at each step after clearing the blocks were detected using the vertical force with a threshold of 20 N. ...
... The location of the ground contact foot after clearing the blocks was defined as the center of pressure of GRF on the ground (mean of the center of pressure position for 0.01 s during the middle of the support phase), and the distance between the foot locations of two consecutive steps was then calculated. 12,15 Running speed was computed by dividing the step distance by the step duration at each step. Average horizontal external power (AHEP) at each step was computed in accordance with a previous study. ...
Rates of ground reaction force development are associated with running speed during sprint acceleration
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This study aimed to investigate the relationship between overground sprint performance and rates of force development (RFDs) in ground reaction forces (GRF) during the entire acceleration phase. Thirty-one male sprinters performed 60-m sprints during which the GRF from the start to the 50-m mark were measured. The vertical, braking and propulsive RFDs at each step were calculated as the average rate of change in GRF. Average values for each four steps during the acceleration phase were calculated to examine relationships between running speed or average horizontal external power (AHEP) and RFD values. The RFD values ranged from 859.8 ± 191.1 to 1682.0 ± 258.2 N/s/kg for vertical force, −502.6 ± 215.7 to −1033.8 ± 196.2 N/s/kg for braking force, and 97.2 ± 11.7 to 185.4 ± 32.3 N/s/kg for propulsive force. There were associations of running speed with vertical RFD at the 21 st –24 th step section (r = 0.385) and with propulsive RFD at the 1 st –4 th step section and from the 13 th –16 th to 21 st –24 th step sections (r = 0.386–0.559). Moreover, AHEP was correlated with vertical RFD from the 13 th –16 th to 21 st –24 th step sections (r = 0.442–0.523), with braking RFD at the 17 th –20 th and 21 st –24 th step sections (r = −0.423 and −0.448), and with propulsive RFD at every step section (r = 0.374–0.856). In conclusion, greater propulsive RFD throughout the acceleration phase, along with higher braking and vertical RFD during the later acceleration section, may indicate better sprint performance.
View
... The corresponding values during the acceleration stage of maximal sprinting change dramatically with increasing running velocity. 9,15,16 However, in the training field, the practical use of the apparatus for measuring spatiotemporal and GRF variables is limited. In particular, force plates are expensive, and preparing a large number of them to determine the GRF at every step over the entire acceleration stage is challenging. ...
... All test trials were performed on an indoor track with a 50-m force plate system where a series of 54 force plates (TF-90100, TF-3055, and TF-32120; Tec Gihan, Uji, Japan) were embedded. 9,15,[24][25][26] The loading device was placed approximately 3 m behind the starting line and the cord from the motor was held at the waist of the runner using a belt. The participants performed one trial per loading condition in ascending order of the load. ...
... An example of the measured and calculated data obtained using the force plate method is shown in Figure 2. F ap and F ver during sprint acceleration were obtained at a sampling rate of 1000 Hz using the 50-m force plate system. 9,15,[24][25][26] The force data were filtered using a fourthorder zero-lag low-pass Butterworth filter with a cutoff of 50 Hz. 9,15,29 The magnitude of F res was calculated as the vector sum of F ap and F ver . ...
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We aimed to examine the validity of estimating spatiotemporal and ground reaction force (GRF) parameters during resisted sprinting using a robotic loading device (1080 Sprint). Twelve male athletes (age: 20.9 ± 2.2 years; height: 174.6 ± 4.2 cm; weight: 69.4 ± 6.1 kg; means ± SDs) performed maximal resisted sprinting with three different loads using the device. The step frequency and length and step‐averaged velocity, anteroposterior GRF (Fap), and the ratio of Fap to resultant GRF (RF) were estimated using the velocity and towing force data measured using the device. Simultaneously, the corresponding values were measured using a 50‐m force plate system. The proportional and fixed biases of the estimated values against those measured using the force plate system were determined using ordinary least product (OLP) regression analysis. Proportional and fixed biases were observed for most variables. However, the proportional bias was small or negligible except for the step frequency. Conversely, the fixed bias was small for step‐averaged velocity (0.11 m/s) and step length (0.04 m), whereas it was large for step frequency (0.54 step/s), Fap (16N), and RF (2.22%). For all variables except step frequency, the prediction intervals in the OLP regression dramatically decreased when the corresponding values were smoothed using a two‐step moving average. These results indicate that by using the velocity and force data recorded in the loading device, most of the spatiotemporal and GRF variables during resisted sprinting can be estimated with some correction of the fixed bias and data smoothing using the two‐step moving average.
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... Although runners' subjective perceptions support this phenomenon, few studies [20,21] support this with objective evidence. According to some data, carbon-plated spikes likely alter the sprinting movement's structure by strengthening the ankle joint's stiffness [22][23][24], which produces more elastic energy [25][26][27] and thus enhances the muscles' stretch-shortening cycle [17,18]. It has been documented that in sprints, spikes transfer more force to the ground [21,28]. ...
... This phenomenon can be explained by analyzing two opposing actions: the accumulation or loss of kinetic energy [25,27,[39][40][41] in the support phase of the sprint step performed both in the acceleration and top speed phases. Sprint performance depends on acceleration and maximum speed [13,42], and this is related to the magnitude of horizontal ground reaction force a sprinter can generate [22,24,[43][44][45] at a specific running velocity. A sprinter's force-velocity profile can describe this [44]. ...
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The main goal of this study was to determine whether the type of spike can influence the final sprint result by comparing step by step the kinematics of four 50-m sprints. Twelve well-trained junior sprinters (ages 17-19) from the Polish National Team (ranging from 100 to 400 m) participated in the study, with personal bests in the 100-m sprint of 10.70 ± 0.19 s. The OptoJump Next-Microgate sensor measurement system (Optojump, Bolzano, Italy) was used to measure the essential kinematic sprinting variables. Following the sprint distance, photocells were placed on the track at the start, at 10 m, at 20 m, at 30 m, and at the finish (50 m). Fifty-meter sprints were completed alternately, two with classic and two with the carbon-plated spikes. For every sprinter, the order in which the spikes were chosen was randomized. To better understand the problem of variability in kinematic parameters, in addition to the actual statistics, the profile analysis process was applied. The analysis of the four 50 m sprints did not show significant differences between the kinematic parameters considering runs in both the classic Nike and carbon-plated Nike ZoomX Flymax spikes. It may be suggested that spikes' sole bending stiffness may not affect short-distance (up to 50-60 m) sprinting performance. From a practical point of view, training focused on maximum speed development can be carried out with both classic and carbon-plated spikes. Finally, our experiment can guide the preparation of a research methodology that assesses the effect of carbon-plated spikes on prolonged sprinting, e.g., 200-400 m.
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... A surplus in propulsive forces results in acceleration, where a surplus of braking forces results in deceleration. If an athlete performs 2 steps per second, that means the acceleration data change significantly at each single step [32]. This suggests that acceleration data might be more variable and higher than what is currently indicated by GNSS devices. ...
... The amplitude of the manufacturer-processed acceleration data is lowered to the point where more data exceed the medium threshold (±2 m·s −2 ) but stay below the high threshold (±3 m·s −2 ), as evident by the larger number of efforts in the medium zone compared to the high zone (see Table 5). When looking into the literature, athletes have reached acceleration values between 5-7 m·s −2 [32][33][34][35], suggesting that elite AF players should be able to reach these values. However, the manufacturer-processed data suggest that the elite AF players barely reach the set ±3 m·s −2 threshold, which is an indication that manufacturer-processed data may be over-smoothing and masking the actual acceleration values that an athlete is capable of. ...
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... The captured volume was approximately 10 m × 1.5 m × 2 m (length × width × height) located at the 40-50 m marks from the start line. Ten force platforms (1.0 × 0.9 m [length × width] each, TF-90100, Tec Gihan, Kyoto, Japan; 1000 hz) as a part of a long force platform system (Nagahara et al., 2018a;Nagahara et al., 2018b;Nagahara, Kanehisa, et al., 2020) located in the capture volume of the motion capture system were used to measure GRF during the trial. The force platforms and the connected running track were covered with a surface that was the same as an official athletic track (Hasegawa Sports Facilities, Tokyo). ...
View
... Excessive repetitive loading can cause greater strain for a given load in ligaments and joint capsules, leading to less effective joint stabilization. Studies have shown that during the take-off phase of jumping, peak ground reaction forces (GRFs) experienced by the take-off leg can reach up to 5933 N, which is about eight times the athlete's body weight and two times the GRF experienced by a sprinter of the same average body mass [4,5]. With single-leg jumping being such a dynamic movement, it is difficult to achieve the same foot strike for every take-off. ...
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... Finally, we averaged the left and the coordinate system (GCS) was aligned with the straightline lane. 1,2,4,6,16,[18][19][20][21]22 In our study, the anterior-posterior component of the FP was also aligned with the straight-line lane (see Data S1 for the entire GCS rotation processing details). In the curve, the anterior-posterior component of the FP was aligned with the curve lane by calculating the angle ( ) between a vector following the FP anteroposterior axis (the black arrow) and the reconstructed curve 23 at each 0.10 m along the curve. ...
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... There are transitions in a linear sprint race that are traditionally broken into start, acceleration, maximum speed and deceleration phases. Further breakpoints have been shown within the acceleration phase, separating acceleration into the initial, middle and later acceleration sections which have unique kinematics and kinetics (Nagahara et al., 2014(Nagahara et al., , 2020. Results showed that the maximum speed phase identified in the control trials was indicative of the maximum speed phase (or occurred near the end of the later acceleration section), and the matching comparisons from the assisted trials occurred during the middle acceleration section (approximately the 12 th step around 20-21 m mark). ...
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The use of digital technology to improve physical education learning of technical skills: case of sprint running
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Purpose: in the last few years, the use of digital technology (DT) as support in teaching and learning has grown significantly. However, its implication and benefits in teaching physical education seems to be a neglected topic.Methods: a randomized controlled experimental study was conducted to investigate the effect a four-week period of alternating video observation (VO) with classical teaching of a physical education program on the kinematics of lower body joint and trunk angles in the sagittal plane at the “set” position of a sprint starts and their outcomes on the starting-blocks clearance performance and short distance sprint running performance within male middle school students. (62) students were equally allocated to a control group (CG, n=31;\mathrm{n}=31;Mean ± SD: age: 14.4±0.814.4\pm 0.8 years; body mass: 52±7.4kg52\pm 7.4\mathrm{kg}; height: 165±10.1165\pm 10.1 cm) and a video observation group (VOG, n=31;\mathrm{n}=31;Mean ± SD: age: 14.8±0.614.8\pm 0.6 years; body mass: 54.3±6.5kg54.3\pm 6.5\mathrm{kg}; height: 162 ±9.5 cm) their kinematics of lower body joint and trunk angles in the sagittal plane at the “set” position from a starting block and sprint performance were tested before and after 4-weeks intervention.Results: for kinematics of sagittal plane at the “set” position, the VOG adapted a more privileged and secure posture on blocks after intervention: rear leg knee angle (from 112.9±29∘112.9\pm 29^{\circ} to 118.0±7.4∘)118.0\pm 7.4^{\circ}), front leg knee angle (from 98.7±14.0∘98.7\pm 14.0^{\circ} to 92±3.84∘92\pm 3.84^{\circ}) and trunk lean angle (from 23.2±8.75∘23.2\pm 8.75^{\circ} to 21.05±5.7∘21.05\pm 5.7^{\circ}), all changes were at significant level of <5%. For the performance over 5m, 10m sprint and block clearance times, the VOG presented moderate (d=−2;p=0.011 d=-2; p=0.011), very large (d=−3.9;p=0.017d=-3.9; p=0.017) and large (d=−1.1;p=0.048d=-1.1; p=0.048) improvement in performance (lower values) for 5m time, for 10m time and for block clearance times, respectively. However, the changes for the CG weren’t statistically significant at p<0.05p\lt0.05.Conclusion: The present study’s findings revealed that an alternate of video visualization and classical physical education teaching improved the kinematics of lower body joint and trunk angles in the sagittal plane at the “set” position of a sprint start, as well as the starting blocks clearance performance and short distance sprint running performance.
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  • Apr 2017
  • Biol Open
This study investigated changes in lower-extremity joint work and power during the swing phase in a maximal accelerated sprinting. Twelve male sprinters performed 60-m maximal sprints while motion data was recorded. Lower-extremity joint work and power during the swing phase of each stride for both legs were calculated. Positive hip and negative knee work (≈4.3 and ≈-2.9 J·kg(-1)) and mean power (≈13.4 and ≈-8.7 W·kg(-1)) during the entire swing phase stabilized or decreased after the 26.2±1.1 (9.69±0.25 m·s(-1)) or 34.3±1.5 m mark (9.97±0.26 m·s(-1)) during the acceleration phase. In contrast, the hip negative work and mean power during the early swing phase (≈7-fold and ≈3.7-fold increase in total), as well as the knee negative work and power during the terminal swing phase (≈1.85-fold and ≈2-fold increase in total), increased until maximal speed. Moreover, only the magnitudes of increases in negative work and mean power at hip and knee joints during the swing phase were positively associated with the increment of running speed from the middle of acceleration phase. These findings indicate that the roles of energy generation and absorption at the hip and knee joints shift around the middle of the acceleration phase as energy generation and absorption at the hip during the late swing phase and at the knee during early swing phase are generally maintained or decreased, and negative work and power at hip during the early swing phase and at knee during the terminal swing phase may be responsible for increasing running speed when approaching maximal speed.
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Are peak ground reaction forces related to better sprint acceleration performance?
Article
  • Jan 2019
This study aimed to elucidate whether the peak (maximum) ground reaction force (GRF) can be used as an indicator of better sprint acceleration performance. Eighteen male sprinters performed 60-m maximal effort sprints, during which GRF for a 50-m distance was collected using a long force platform system. Then, step-to-step relationships of running acceleration with mean and peak GRFs were examined. In the anteroposterior direction, while the mean propulsive force was correlated with acceleration during the initial acceleration phase (to the 5th step) (r = 0.559–0.713), peak propulsive force was only correlated with acceleration at the 9th step (r = 0.481). Moreover, while the mean braking force was correlated with acceleration at the 20th and 22nd steps (r = 0.522 and 0.544, respectively), peak braking force was not correlated with acceleration at all steps. In the vertical direction, significant negative correlations of mean and peak vertical forces with acceleration were found at the same steps (16th, 20th and 22nd step). These results indicate that while the peak anteroposterior force cannot be an indicator of sprint acceleration performance, the peak vertical force is likely an indicator for achieving better acceleration during the later stage of maximal acceleration sprinting.
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How sprinters accelerate beyond the velocity plateau of soccer players: Waveform analysis of ground reaction forces
Article
  • Sep 2018
Forces applied to the ground during sprinting are vital to performance. This study aimed to understand how specific aspects of ground reaction force waveforms allow some individuals to continue to accelerate beyond the velocity plateau of others. Twenty‐eight male sprint specialists and 24 male soccer players performed maximal‐effort 60‐m sprints. A 54‐force‐plate system captured ground reaction forces, which were used to calculate horizontal velocity profiles. Touchdown velocities of steps were matched (8.00, 8.25 and 8.50 m·s⁻¹) and the subsequent ground contact forces were analysed. Mean forces were compared across groups and statistical parametric mapping (t‐tests) assessed for differences between entire force waveforms. When individuals contacted the ground with matched horizontal velocity, ground contact durations were similar. Despite this, sprinters produced higher average horizontal power (15.7‐17.9 W·kg⁻¹) than the soccer players (7.9‐11.9 W·kg⁻¹). Force waveforms did not differ in the initial braking phase (0‐~20% of stance). However, sprinters attenuated eccentric force more in the late braking phase and produced a higher anteroposterior component of force across the majority of the propulsive phase, for example from 31‐82% and 92‐100% of stance at 8.5 m·s⁻¹. At this velocity, resultant forces were also higher (33‐83% and 86‐100% of stance) and the force vector was more horizontally orientated (30‐60% and 95‐98% of stance) in the sprinters. These findings illustrate the mechanisms which allowed the sprinters to continue accelerating beyond the soccer players’ velocity plateau. Moreover, these force production demands provide new insight regarding athletes’ strength and technique training requirements to improve acceleration at high velocity. This article is protected by copyright. All rights reserved.
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Phase analysis in maximal sprinting: an investigation of step-to-step technical changes between the initial acceleration, transition and maximal velocity phases
Article
  • Jul 2018
The aim of this study was to investigate spatiotemporal and kinematic changes between the initial acceleration, transition and maximum velocity phases of a sprint. Sagittal plane kinematics from five experienced sprinters performing 50-m maximal sprints were collected using six HD-video cameras. Following manual digitising, spatiotemporal and kinematic variables at touchdown and toe-off were calculated. The start and end of the transition phase were identified using the step-to-step changes in centre of mass height and segment angles. Mean step-to-step changes of spatiotemporal and kinematic variables during each phase were calculated. Firstly, the study showed that if sufficient trials are available, step-to-step changes in shank and trunk angles might provide an appropriate measure to detect sprint phases in applied settings. However, given that changes in centre of mass height represent a more holistic measure, this was used to sub-divide the sprints into separate phases. Secondly, during the initial acceleration phase large step-to-step changes in touchdown kinematics were observed compared to the transition phase. At toe-off, step-to-step kinematic changes were consistent across the initial acceleration and transition phases before plateauing during the maximal velocity phase. These results provide coaches and practitioners with valuable insights into key differences between phases in maximal sprinting.
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Kinetic demands of sprinting shift across the acceleration phase: Novel analysis of entire force waveforms
Article
  • Apr 2018
A novel approach of analysing complete ground reaction force waveforms rather than discrete kinetic variables can provide new insight to sprint biomechanics. This study aimed to understand how these waveforms are associated with better performance across entire sprint accelerations. Twenty‐eight male track and field athletes (100‐m personal best times: 10.88 to 11.96 s) volunteered to participate. Ground reaction forces produced across 24 steps were captured during repeated (two to five) maximal‐effort sprints utilising a 54‐force‐plate system. Force data (anteroposterior, vertical, resultant and ratio of forces) across each contact were registered to 100% of stance and averaged for each athlete. Statistical parametric mapping (linear regression) revealed specific phases of stance where force was associated with average horizontal external power produced during that contact. Initially, anteroposterior force production during mid‐late propulsion (e.g. 58‐92% of stance for the second ground contact) was positively associated with average horizontal external power. As athletes progressed through acceleration, this positive association with performance shifted towards the earlier phases of contact (e.g. 55‐80% of stance for the eighth and 17‐57% for the 19th ground contact). Consequently, as athletes approached maximum velocity, better athletes were more capable of attenuating the braking forces, especially in the latter parts of the eccentric phase. These unique findings demonstrate a shift in the performance determinants of acceleration from higher concentric propulsion to lower eccentric braking forces as velocity increases. This highlights the broad kinetic requirements of sprinting and the conceivable need for athletes to target improvements in different phases separately with demand‐specific exercises. This article is protected by copyright. All rights reserved.
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Age-Related Differences in Spatiotemporal Variables and Ground Reaction Forces During Sprinting in Boys
Article
  • Feb 2018
Purpose: We aimed to elucidate age-related differences in spatiotemporal and ground reaction force variables during sprinting in boys over a broad range of chronological ages. Methods: Ground reaction force signals during 50-m sprinting were recorded in 99 boys aged 6.5-15.4 years. Step-to-step spatiotemporal variables and mean forces were then calculated. Results: There was a slower rate of development in sprinting performance in the age span from 8.8 to 12.1 years compared with younger and older boys. During that age span, mean propulsive force was almost constant, and step frequency for older boys was lower regardless of sprinting phase. During the ages younger than 8.8 years and older than 12.1 years, sprint performance rapidly increased with increasing mean propulsive forces during the middle acceleration and maximal speed phases and during the initial acceleration phase. Conclusion: There was a stage of temporal slower development of sprinting ability from age 8.8 to 12.1 years, being characterized by unchanged propulsive force and decreased step frequency. Moreover, increasing propulsive forces during the middle acceleration and maximal speed phases and during the initial acceleration phase are probably responsible for the rapid development of sprinting ability before and after the period of temporal slower development of sprinting ability.
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Vertical Impulse as a Determinant of Combination of Step Length and Frequency During Sprinting
Article
  • Feb 2018
This study aimed to clarify the influence of vertical impulse on the magnitude of step length (SL) and frequency (SF) and their ratio during the entire acceleration phase of maximal sprinting. Thirty-nine male soccer players performed 60-m sprints, during which step-to-step ground reaction forces were recorded over a 50-m distance. The mean values of spatiotemporal variables and vertical and anteroposterior impulses for each set of four steps during the acceleration phase until the 28th step were computed to examine relationships among variables in seven sections. When controlling for the influence of running speed, stature and corresponding duration of braking or propulsion, vertical impulses during the propulsive phase at the 1st–4th step section and those during the braking phases in the sections from the 5th–8th to the 25th–28th step were positively correlated with SL and SL/SF ratio and negatively correlated with SF, whereas the anteroposterior impulses were not correlated with SL or SF. In conclusion, the current results demonstrate that vertical impulse during the propulsive phase in the initial acceleration stage and that during the braking phase in the middle and later acceleration stages are the most likely determinants of the combination of SL and SF during sprinting.
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Step-to-step spatiotemporal variables and ground reaction forces of intra-individual fastest sprinting in a single session
Article
  • Oct 2017
We aimed to investigate the step-to-step spatiotemporal variables and ground reaction forces during the acceleration phase for characterising intra-individual fastest sprinting within a single session. Step-to-step spatiotemporal variables and ground reaction forces produced by 15 male athletes were measured over a 50-m distance during repeated (three to five) 60-m sprints using a long force platform system. Differences in measured variables between the fastest and slowest trials were examined at each step until the 22nd step using a magnitude-based inferences approach. There were possibly–most likely higher running speed and step frequency (2nd to 22nd steps) and shorter support time (all steps) in the fastest trial than in the slowest trial. Moreover, for the fastest trial there were likely–very likely greater mean propulsive force during the initial four steps and possibly–very likely larger mean net anterior–posterior force until the 17th step. The current results demonstrate that better sprinting performance within a single session is probably achieved by 1) a high step frequency (except the initial step) with short support time at all steps, 2) exerting a greater mean propulsive force during initial acceleration, and 3) producing a greater mean net anterior–posterior force during initial and middle acceleration.
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Association of Sprint Performance With Ground Reaction Forces During Acceleration and Maximal Speed Phases in a Single Sprint
Article
  • Sep 2017
We aimed to clarify the mechanical determinants of sprinting performance during acceleration and maximal speed phases of a single sprint, using ground reaction forces (GRFs). While 18 male athletes performed a 60-m sprint, GRF was measured at every step over a 50-m distance from the start. Variables during the entire acceleration phase were approximated with a fourth-order polynomial. Subsequently, accelerations at 55%, 65%, 75%, 85%, and 95% of maximal speed, and running speed during the maximal speed phase were determined as sprinting performance variables. Ground reaction impulses and mean GRFs during the acceleration and maximal speed phases were selected as independent variables. Stepwise multiple regression analysis selected propulsive and braking impulses as contributors to acceleration at 55%-95% (β > 0.724) and 75%-95% (β > 0.176), respectively, of maximal speed. Moreover, mean vertical force was a contributor to maximal running speed (β = 0.481). The current results demonstrate that exerting a large propulsive force during the entire acceleration phase, suppressing braking force when approaching maximal speed, and producing a large vertical force during the maximal speed phase are essential for achieving greater acceleration and maintaining higher maximal speed, respectively.
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Association of Step Width with Accelerated Sprinting Performance and Ground Reaction Force
Article
  • May 2017
  • INT J SPORTS MED
This study aimed to describe changes in step width (SW) during accelerated sprinting, and to clarify the relationship of SW with sprinting performance and ground reaction forces. 17 male athletes performed maximal-effort 60 m sprints. The SW and other spatiotemporal variables, as well as ground reaction impulses, over a 52 m distance were calculated. Average values for each 4 steps during acceleration were calculated to examine relationships among variables in different sections. The SW rapidly decreased up to the 13th step and slightly afterward during accelerated sprinting, showing a bilinear phase profile. The ratio of SW to the stature was significantly correlated with running speed based on average values over the 52 m distance and in the 9th-12th step section during accelerated sprinting. The SW ratio positively correlated with medial, lateral and mediolateral impulses in all step sections, except for medial impulse in the 17th-20th step section. These results indicate the importance of wider SW for better sprinting performance, especially in the 9th-12th step section. Moreover, the wider SW was associated with larger medial impulse and smaller lateral impulse, suggesting that a wide SW contributes to the production of greater mediolateral body velocity during accelerated sprinting.
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