Age-Related Differences in Spatiotemporal Variables and Ground Reaction Forces During Sprinting in Boys

Spatiotemporal and kinetic characteristics during maximal sprint running in fast running soccer players

This study aimed to elucidate spatiotemporal and kinetic variables in fast-running soccer players in comparison with sprinters or slow-running soccer players. Sixty-seven male soccer players and 17 male sprinters (Sp) performed 60-m maximal effort sprint running. The soccer players were classified into three groups: high-speed (SOCHigh), medium-speed, and low-speed (SOCLow). The antero-posterior and vertical ground reaction forces were measured with a 50-m long force plates system at every step during the sprint. Step length and step frequency were also computed from the position of center of pressure, contact time, and flight time. During the initial acceleration phase, SOCHigh exhibited similar running speeds to Sp. This was attributed to a higher step frequency in SOCHigh compared to Sp, while net antero-posterior impulse was lower in the former than in the later. In the range of running speed from 7.5 m/s to 8.5 m/s, net antero-posterior impulse for SOCHigh was similar to that for Sp. At 9.0 m/s, SOCHigh exhibited a lower net antero-posterior impulse compared to Sp, primarily due to a reduced propulsive impulse. Additionally, vertical impulse during the braking phase was larger in SOCHigh compared to Sp, due to a longer braking time, while vertical impulse during the propulsive phase was smaller, due to a tendency for a reduced propulsive time and vertical force during the corresponding phase. Compared to SOCLow, SOCHigh exhibited higher step frequency through sprint running and longer step lengths from the 2nd acceleration phase to maximal speed phase. Additionally, net antero-posterior impulse at the same running speed was greater in SOCHigh compared to SOCLow. Vertical impulse was lower during the braking phase but higher during the propulsive phase in SOCHigh than in SOCLow. Thus, the sprint mechanics of SOCHigh is characterized by a similar ability of speed acquisition up to the 2nd acceleration as sprinters. However, at 9.0 m/s or over, SOCHigh exhibits a greater vertical impulse, leading to a lower step frequency.

Effects of maximal power and the force-velocity profile on sprint acceleration performance according to maturity status and sex

This study aimed to determine whether maturational and sex-related differences in sprint times were accompanied by changes in relative maximal power (Pmax), force-velocity profiles (SFV) and optimal sprint distances (xopt). Sprint times and continuous velocity-time data were collected using a radar. Inverse dynamics applied to the centre of mass provided accurate estimations of force-velocity relationship parameters (Pmax, F0, v0, SFV, xopt) and technical variables (RFmax, DRF). Somatic maturity was determined from peak height velocity (PHV). Performance increased with maturation in girls and boys (p < 0.001, d = 0.86‒2.78) accompanied by increases in relative Pmax from pre to post-PHV (p < 0.011‒0.001, d = 0.98‒5.20). Increases in relative Pmax were predominantly due to more velocity-oriented profiles (p < 0.007‒0.001, d = 0.76‒1.41). xopt, RFmax and DRF also increased with maturation (p < 0.030‒0.001, d = 0.87‒3.40). Pmax increases in girls and boys throughout maturation enabling them to reduce sprint times. Both girls and boys increased Pmax through a shift to more velocity-oriented profiles. However, plateaus in F0 and RFmax were present from pre-PHV in girls, while boys had slower development from mid-PHV. Improving Pmax through increases in F0 and RFmax, while maintaining a velocity-oriented profile, will likely benefit youth sprint performance. A specific focus on these parameters is necessary from pre-PHV onwards in girls and from mid-PHV in boys.

Repetitive Sprinting and Running Fatigue in Children with Different Levels of Motor Competence

Background: Children with motor delays often experience challenges in health-related fitness, but the impact on running skills remains unclear. Previous research has shown that children with motor coordination problems have lower cardiorespiratory fitness, muscle strength, endurance, and higher body weight compared to peers. Few studies have examined anaerobic capacity, muscular power, endurance, running performance, and fatigue in children with developmental coordination disorder (DCD). This study aims to compare repetitive running and running-induced fatigue in typically developing children and those with varying degrees of motor coordination problems. Methods: Groups were classified using the Movement Assessment Battery for Children, second edition (MABC-2), as probably having DCD (p-DCD, ≤5th percentile, age 9.7 (SD 1.6), n = 141), at risk for DCD (r-DCD, 6th-16th percentile, age 9.9 (SD1.6), n = 160), and typically developing (TD, >16th percentile, age 9.6 (SD 1.6), n = 191). Anaerobic fitness and fatigue were assessed using the Children's Repetitive and Intermittent Sprinting Performance test (CRISP), while lower and upper body muscular strength, running, and agility were measured with the performance and fitness (PERF-FIT) test battery Power and Agility subscale. Age groups (6-9 and 10-12 years) were analyzed to determine when performance deficits emerged. Results: The p-DCD group was significantly slower, had less power, and fatigued more than the r-DCD and TD children (p < 0.01). This was already clearly the case in the 6-9-year-olds, who slowed down already after the first runs, while the older poorly coordinated children started slower than their peers and showed a more gradual decrease in performance over the runs. Conclusions: Moderate coordination differences between r-DCD and TD children did not significantly impact fatigue, but p-DCD children exhibited greater fatigue due to overestimating their start speed, higher body weight, lower power, and reduced agility, especially in younger age groups. (Too) High starting speed, especially in the younger less coordinated children (p-DCD), is likely to lead to more fatigue.

Are sprint accelerations related to groin injuries? A biomechanical analysis of adolescent soccer players

Groin injuries have one of the highest incidences in soccer and can be career threatening, especially for adolescents, due to their high recurrence rate. Quick accelerations have been connected to groin injuries along with kicking and change of directions. Purpose of this study was to examine the hip joint kinematics, kinetics and the muscle forces of adductor longus and gracilis during first ground contact of a linear sprint acceleration performed by adolescent soccer players. Twenty-two male participants were investigated with 3D motion capture and two force plates. Inverse dynamics were used to calculate the kinematics, kinetics and muscle forces. The kinematics show a constant extension during the stance phase and a quick transition from an abduction to an adduction movement at 90% stance, which coincides with the highest forces in adductor longus and gracilis. This indicates a high load on the adductor muscles due to eccentric contractions combined with high muscle forces in the adductors. Compared to previously investigated inside passing and change of direction movements, adductor muscle forces and angular velocities are higher in this study. Therefore, it is suggested that sprint accelerations are likely to be connected to the development of groin injuries in adolescent soccer players.

Normative Reference Centiles for Sprint Performance in High-Level Youth Soccer Players: The Need to Consider Biological Maturity

PURPOSE

To compute reference centiles for 5- and 30-m sprint times relative to chronological and skeletal age in youth soccer players. Subsequently, to compare individual's sprint performance scores derived from the chronological and skeletal age reference centiles.

METHODS

Sprint times were collected for a sample of male U11 to U19 soccer players (n = 1745 data points). Skeletal age data were available for a subsample (n = 776 data points). Reference centiles were fitted using generalized additive models for location, scale, and shape. Individual z scores relative to chronological and skeletal age reference centiles were computed and compared for each maturity group (late, on-time, early, and very early) using standardized mean differences (SMD).

RESULTS

Reference centiles for chronological age increased more rapidly between 10.5 and 15.5 years, while reference centiles for skeletal age increased more rapidly between 13.0 and 16.5 years. Differences in chronological and skeletal z scores for very early (SMD: -0.73 to -0.43) and late (SMD: 0.58 to 1.29) maturing players were small to large, while differences for early (SMD: -0.30 to -0.19) and on-time (SMD: 0.16 to 0.28) were trivial to small.

CONCLUSION

Reference centiles provide a valuable tool to assist the evaluation of sprint performance in relation to chronological and skeletal age for talent identification purposes in youth soccer players.

Influence of Growth, Maturation, and Sex on Maximal Power, Force, and Velocity During Overground Sprinting

ABSTRACT

Sudlow, A, Galantine, P, Del Sordo, G, Raymond, J-J, Dalleau, G, Peyrot, N, and Duché, P. Influence of growth, maturation, and sex on maximal power, force, and velocity during overground sprinting. J Strength Cond Res 38(3): 491-500, 2024-In pediatric populations maximal anaerobic power, force, and velocity capabilities are influenced by changes in body dimensions and muscle function. The aim of this study was to investigate the influences of growth, maturation, and sex on short-term anaerobic performance. One hundred forty children pre-, mid-, and postpeak height velocity performed two 30-m sprints concurrently measured using a radar device. Maximal power (Pmax), force (F0), and velocity (v0) were calculated from sprint velocity-time data and normalized using sex-specific, multiplicative, allometric models containing body mass, fat-free mass (FFM), or height, and chronological age. Absolute values for Pmax, F0, and v0 were higher with increasing maturity (p < 0.01; d ≥ 0.96), and boys had greater outputs than girls (p < 0.01; d ≥ 1.19). When Pmax and v0 were scaled all maturity-related and sex-related differences were removed. When F0 was scaled using models excluding age, all maturity-related differences were removed except for the least mature group (p < 0.05; d ≥ 0.88) and boys maintained higher values than girls (p < 0.05; d ≥ 0.92). All maturity-related and sex-related differences were removed when F0 was scaled using models including age. Maturity-related and sex-related variance in Pmax and v0 can be entirely explained when FFM, height, and chronological age are accounted for. Regarding F0, there seems to be a threshold after which the inclusion of age is no longer necessary to account for maturity-related differences. In young prepubertal children, the inclusion of age likely accounts for deficits in neuromuscular capacities and motor skills, which body dimensions cannot account for. Practitioners should focus on eliciting neural adaptations and enhancing motor coordination in prepubertal children to improve anaerobic performance during overground sprinting.

In-situ acceleration-speed profile of an elite soccer academy: A cross-sectional study

Speed is an essential skill in sports performance and an important performance metric in talent identification. This study aims to evaluate and compare the sprint acceleration characteristics across different age groups in an elite soccer academy. A total of 141 elite academy soccer players were recruited to participate in the study, and they were assigned to their respective competitive age groups, ranging from under-14 to the B-team. An individual in-situ acceleration-speed (A-S) profile was assessed and derived from Global Position System (GPS) speed-acceleration raw data, from 10 consecutive football sessions, in the beginning of the season. The results showed that under-14 players exhibited significantly lower theoretical maximum speed (S0) (η p 2  = 0.215, p < 0.01) when compared with all other age groups. However, no differences were found between maximum theoretical acceleration (A0) and A-S slope between age groups. The results suggest that sprint mechanical profiles of young soccer athletes remain stable throughout their athletic development. Nevertheless, younger athletes have less capacity to apply horizontal force at higher speeds (S0).

Which Factors Influence Running Gait in Children and Adolescents? A Narrative Review

In recent years, running has dramatically increased in children and adolescents, creating a need for a better understanding of running gait in this population; however, research on this topic is still limited. During childhood and adolescence multiple factors exist that likely influence and shape a child's running mechanics and contribute to the high variability in running patterns. The aim of this narrative review was to gather together and assess the current evidence on the different factors that influence running gait throughout youth development. Factors were classified as organismic, environmental, or task-related. Age, body mass and composition, and leg length were the most researched factors, and all evidence was in favour of an impact on running gait. Sex, training, and footwear were also extensively researched; however, whereas the findings concerning footwear were all in support of an impact on running gait, those concerning sex and training were inconsistent. The remaining factors were moderately researched with the exception of strength, perceived exertion, and running history for which evidence was particularly limited. Nevertheless, all were in support of an impact on running gait. Running gait is multifactorial and many of the factors discussed are likely interdependent. Caution should therefore be taken when interpreting the effects of different factors in isolation.

Influence of age and maturation status on sprint acceleration characteristics in junior Australian football

This study aimed to investigate the influence of chronological age and maturation status on sprint acceleration characteristics in junior Australian football (AF) players. Biological maturity of 109 subjects was assessed and subjects were grouped according to predicted years from peak height velocity (PHV) (pre-, mid-, and post-PHV) and chronological age (13 years, 14 years, and 15 years). A one-way multivariate analysis of variance and magnitude-based decisions were used to determine between-group differences. Instantaneous velocity was measured during two maximal 30m sprints via radar gun with the velocity-time data used to derive the force, velocity, and power characteristics. Chronologically, the greatest differences were observed between the 13 and 14 year old groups with the latter group producing likely greater relative maximum power (Pmax) (ES[effect size]=0.44) and theoretical maximal velocity (V0) (ES=0.49). The post-PHV group likely demonstrated a greater ability to apply force at faster velocity (V0; ES=0.59) and orient the force in a horizontal direction (Drf%; ES=-0.49) than the mid-PHV group. No differences in relative theoretical maximal force (F0) were observed between groups. Considering the findings, practitioners should aim to improve relative lower limb strength through heavy sled push or sled pulls and traditional strength training exercises to improve relative F0.

Acceleration mechanics during forward and backward running: A comparison of step kinematics and kinetics over the first 20 m

Backward running (BR) and forward running (FR) are unique movements utilized by athletes in many sports. Importantly, this investigation provides further insights on BR and benchmarking against more commonly researched FR capacity. Twenty-one collegiate soccer players (age 20.0 ± 0.8 years, body mass 65.6 ± 7.7 kg, body height 1.70 ± 0.07 m) performed maximal effort BR and FR along 20 m of in-ground force platforms. Step kinematics and kinetics were compared between BR and FR over four relative acceleration phases (BR = steps 1-6, 7-12, 13-18 and 19-23; FR = steps 1-4, 5-8, 9-12, 13-15). The primary findings of this study were that BR speeds were 29% slower than FR (p < 0.001), all step kinematics differed between BR and FR (p < 0.01), except contact time from the second to fourth step phases (p > 0.05), and most step kinetics were lower during BR (p < 0.05), with the exceptions of peak vertical force (p > 0.05). These findings indicate that lower running speeds over the acceleration phases of BR appear to be primarily due to lower horizontal ground reaction force application, resulting in shorter stride lengths and decreased flight times compared to FR.

The Kinematic and Kinetic Development of Sprinting and Countermovement Jump Performance in Boys

Background

The aim of the study was to examine the kinematics and kinetics of sprint running and countermovement jump performance between the ages of 8–9, and 11–12 years old boys in order to understand the developmental plateau in performance.

Methods

18 physically active boys (Age: 10.1 ± 1.6), in an under 9 years old (U9) and an under 12 years old (U12) group performed 15 m sprints and countermovement jumps. A 3D motion analysis system (200 Hz), synchronized with four force platforms (1,000 Hz), was used to collect kinematic and kinetic data during the first stance phase of the sprint run and the countermovement jump.

Results

The U12 group had a significantly greater height (U9: 1.364 ± 0.064 m; U12: 1.548 ± 0.046 mm), larger mass (U9: 30.9 ± 3.5 kg; U12: 43.9 ± 5.0 kg), superior sprint performance over 0–5 m (U9: 1.31 ± 0.007 s; U12: 1.23 ± 0.009 s) and 0–15 m (U9: 3.20 ± 0.17 s; U12: 3.01 ± 0.20 s), and increased jump height (U9: 0.17 ± 0.06 m; U12: 0.24 ± 0.10 m) than the under nine group. During the first stance phase of the sprint the U12 group had a significantly greater vertical (U9: 0.22 ± 0.02 BW/s; U12: 0.25 ± 0.03 BW.s) and horizontal impulse (U9: 0.07 ± 0.02 BW/s; U12: 0.09 ± 0.03 BW.s) than the U9 group. When performing a countermovement jump the U12 group had a significantly greater mean average eccentric force (U9: 407.3 ± 55.0 N; U12: 542.2 ± 65.1 N) and mean average concentric force (U9: 495.8 ± 41.3 N; U12: 684.0 ± 62.1 N). Joint kinematics for the countermovement jump were significantly different between age groups for the ankle range of motion (U9: 80.6 ± 17.4°; U12: 64.1 ± 9°) and knee minimum joint angle (U9: −5.7 ± 3.9°; U12: 0.0 ± 4.4°). Conclusion: The study demonstrates for the first time that the development of physically active boys between the ages of 8–9 to 11–12 years increased the ground reaction forces and impulses during sprint running and countermovement jumps, but that sprint running technique had not developed during this period. Furthermore, countermovement jump technique was still emerging at the age of 8–9 years old. Practitioners need to implement on-going fine-grained sprint running and CMJ technique sessions to ensure that the increased force producing capabilities that come with age are appropriately utilized.

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

Cahill, MJ, Oliver, JL, Cronin, JB, Clark, K, Cross, MR, Lloyd, RS, and Lee, JE. Influence of resisted sled-pull training on the sprint force-velocity profile of male high-school athletes. J Strength Cond Res 34(10): 2751-2759, 2020-Although resisted sled towing is a commonly used method of sprint-specific training, little uniformity exists around training guidelines for practitioners. The aim of this study was to assess the effectiveness of unresisted and resisted sled-pull training across multiple loads. Fifty-three male high-school athletes were assigned to an unresisted (n = 12) or 1 of 3 resisted groups: light (n = 15), moderate (n = 14), and heavy (n = 12) corresponding to loads of 44 ± 4 %BM, 89 ± 8 %BM, and 133 ± 12 %BM that caused a 25, 50, and 75% velocity decrement in maximum sprint speed, respectively. All subjects performed 2 sled-pull training sessions twice weekly for 8 weeks. Split times of 5, 10, and 20 m improved across all resisted groups (d = 0.40-1.04, p < 0.01) but did not improve with unresisted sprinting. However, the magnitude of the gains increased most within the heavy group, with the greatest improvement observed over the first 10 m (d ≥ 1.04). Changes in preintervention to postintervention force-velocity profiles were specific to the loading prescribed during training. Specifically, F0 increased most in moderate to heavy groups (d = 1.08-1.19); Vmax significantly decreased in the heavy group but increased in the unresisted group (d = 012-0.44); whereas, Pmax increased across all resisted groups (d = 0.39-1.03). The results of this study suggest that the greatest gains in short distance sprint performance, especially initial acceleration, are achieved using much heavier sled loads than previously studied in young athletes.

Effects of Supplementary Strength-Power Training on Neuromuscular Performance in Young Female Athletes

This study examined the effects of a short-duration supplementary strength–power training program on neuromuscular performance and sport-specific skills in adolescent athletes. Twenty-three female “Gymnastics for All” athletes, aged 13 ± 2 years, were divided into a training group (TG, n = 12) and a control group (CG, n = 11). Both groups underwent a test battery before and after 10 weeks of intervention. TG completed, in addition to gymnastics training, a supplementary 7–9 min program that included two rounds of strength and power exercises for arms, torso, and legs, executed in a circuit fashion with 1 min rest between rounds, three times per week. Initially, six exercises were performed (15 s work–15 s rest), while the number of exercises was decreased to four and the duration of each exercise was increased to 30 s (30 s rest) after the fifth week. TG improved countermovement jump performance with one leg (11.5% ± 10.4%, p = 0.002) and two legs (8.2% ± 8.8%, p = 0.004), drop jump performance (14.4% ± 12.6%, p = 0.038), single-leg jumping agility (13.6% ± 5.2%, p = 0.001), and sport-specific performance (8.8% ± 7.4%, p = 0.004), but not 10 m sprint performance (2.4% ± 6.6%, p = 0.709). No change was observed in the CG (p = 0.41 to 0.97). The results of this study indicated that this supplementary strength–power program performed for 7–9 min improves neuromuscular and sport-specific performance after 10 weeks of training.

The effect of biological maturity status on ground reaction force production during sprinting

Sprint ability develops nonlinearly across childhood and adolescence. However, the underpinning ground reaction force (GRF) production is not fully understood. This study aimed to uncover the kinetic factors that explain these maturation-related sprint performance differences in Japanese boys and girls. A total of 153 untrained schoolchildren (80 boys, 73 girls) performed two 50-m maximal effort sprints over a 52-force-platform system embedded in an indoor track. Maturity offset (years from peak height velocity; PHV) was estimated using anthropometric data and used to categorise the children into six-year-long maturation groups (from group 1 [5.5-4.5 years before PHV] to group 6 [0.5 years before to 0.5 years after PHV). Maximum and mean step-averaged velocities across 26 steps were compared across consecutive maturation groups, with further GRF analysis (means and waveforms [statistical parametric mapping]) performed when velocity differences were observed. For boys, higher maximum velocities (effect size ± 90% CI = 1.63 ± 0.69) were observed in maturation group 2 (4.5-3.5 years before PHV) compared to group 1 (5.5-4.5 years before PHV), primarily attributable to higher antero-posterior GRFs across shorter ground contacts. Maximum velocities increased from maturation group 4 (2.5-1.5 years before PHV) to group 5 (1.5-0.5 years before PHV) in the girls (effect size ± 90% CI = 1.00 ± 0.78), due to longer ground contacts rather than higher GRFs per se. Waveform analyses revealed more effective reversal of braking forces and higher propulsive forces (e.g. 14%-77% of stance 4), particularly for comparisons involving boys, which suggested potentially enhanced stretch-shortening ability. Youth sport practitioners should consider these maturation-specific alterations when evaluating young athletes' sprint abilities.

Effects of Plyometric Training on Sprint Running Performance in Boys Aged 9-12 Years

Skilled sprinting is fundamental in many sports, especially to improve athletic performance in youth. This study therefore aimed to investigate the effect of plyometric training on sprint performance in boys aged 9-12 years. Twenty boys were divided into a plyometric training group (n = 9) and a control training group (n = 11). In both groups, participants performed respective training programs once per week for 8 weeks with measurements at baseline and post-intervention. Sprint performance was assessed by 50-m sprint time, sprint velocity, step frequency and step length at 10-m intervals. Jumping performance was assessed using horizontal, vertical and rebound jumps. The plyometric training group showed an improved sprint velocity at 20-30 m, 30-40 m and 40-50 m, and step length at 0-10 m, 20-30 m and 30-40 m (p < 0.05). Furthermore, only the plyometric group showed an increased standing long jump distance and rebound jump performance (p < 0.05). The control group did not show any significant changes in any variable. Our findings suggest that plyometric training in pre-adolescent boys improves sprint velocity and step length at the maximum velocity phase concomitant with increased horizontal and rebound jump performance.

Age-related differences in kinematics and kinetics of sprinting in young female

This study aimed to investigate the age-related differences in sprinting performance, kinematic and kinetic variables in girls aged between 7.0 and 15.3 years. Step-to-step spatiotemporal variables and ground reaction impulses during sprinting were collected in 94 Japanese girls across a 50 m inground force plate system. From the results, a difference in rate of development in sprinting performance in girls over 12.7 years compared with younger girls (YG) was observed. The older girls (OG) became slightly slower each year (-0.09 m/s/y) compared to the YG (0.24 m/s/y) who increased their running speed. Moreover, height increased by 6.3 cm/y in YG and only 3.6 cm/y in OG, while step length during the maximal speed phase increased by 0.08 m/y in YG and plateaued in OG (0.01 m/y). Propulsive impulse during the initial acceleration phase was the kinetic variable to differ in rate of development between the age groups with an increase of 0.024 Ns/y in the YG compared to -0.010 Ns/y in OG. The development of sprinting ability in Japanese girls was more rapid before age 12.7 years. The difference in rate of development in sprinting ability can be primarily attributed to greater growth rates in YG, contributing to increases in the propulsive impulse during the initial acceleration phase and step length during the maximal speed phase. The limited gains in step length and the propulsive impulse in OG may reflect their reduced growth rate in height and the fact that increases in fat mass with maturation impaired relative force production.

Kinematic characteristics of barefoot sprinting in habitually shod children

BACKGROUND

Anecdotally, a wide variety of benefits of barefoot running have been advocated by numerous individuals. The influence of the alterations in the properties of the shoe on the running movement has been demonstrated in adults at submaximal jogging speeds. However, the biomechanical differences between shod and barefoot running in children at sprinting speeds and the potential developmental implications of these differences are still less examined. The purpose was to determine the potential differences in habitually shod children's sprint kinematics between shod and barefoot conditions.

METHODS

Ninety-four children (51 boys and 43 girls; 6-12 years-old; height, 135.0 ± 0.12 m; body mass, 29.0 ± 6.9 kg) performed 30 m maximal sprints from standing position for each of two conditions (shod and barefoot). To analyze sprint kinematics within sagittal plane sprint kinematics, a high-speed camera (300 fps) was set perpendicular to the runway. In addition, sagittal foot landing and take-off images were recorded for multiple angles by using five high-speed cameras (300 fps). Spatio-temporal variables, the kinematics of the right leg (support leg) and the left leg (recovery leg), and foot strike patterns: rear-foot strike (RFS), mid-foot strike (MFS), and fore-foot strike (FFS) were investigated. The paired t-test was used to test difference between shod and barefoot condition.

RESULTS

Barefoot sprinting in habitually shod children was mainly characterized by significantly lower sprint speed, higher step frequency, shorter step length and stance time. In shod running, 82% of children showed RFS, whereas it decreased to 29% in barefoot condition. The touch down state and the subsequent joint movements of both support and recovery legs during stance phase were significantly altered when running in condition with barefoot.

DISCUSSION

The acute effects of barefoot sprinting was demonstrated by significantly slower sprinting speeds that appear to reflect changes in a variety of spatiotemporal parameters as well as lower limb kinematics. It is currently unknown whether such differences would be observed in children who typically run in bare feet and what developmental benefits and risks may emerge from increasing the proportion of barefoot running and sprinting in children. Future research should therefore investigate potential benefits that barefoot sprinting may have on the development of key physical fitness such as nerve conduction velocity, muscular speed, power, and sprinting technique and on ways to minimize the risk of any acute or chronic injuries associated with this activity.