The effect of the bend on technique and performance during maximal effort sprinting

Are the ground reaction forces altered by the curve and with the increasing sprinting velocity?

In 200- and 400-m races, 58% of the total distance to cover is in the curve. In the curve, the sprinting performance is decreased in comparison to the straight. However, the reasons for this decreased performance is not well understood. Thus, the aim of this study was to identify the kinetic parameters underpinning the sprinting performance in the curve in comparison to the straight. Nineteen experienced-to-elite curve specialists performed five sprints in the straight and in the curve (radius 41.58 m): 10, 15, 20, 30, and 40 m. The left and the right vertical, anterior-posterior, medial-lateral, and resultant ground reaction forces (respectivelyF V $$ {F}_{\mathrm{V}} $$ ,F A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ ,F M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ , andF TOT $$ {F}_{\mathrm{TOT}} $$ ), the associated impulses (respectivelyIMP V $$ {IMP}_{\mathrm{V}} $$ ,IMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ ,IMP M - L $$ {IMP}_{\mathrm{M}-\mathrm{L}} $$ , andIMP TOT $$ {IMP}_{\mathrm{TOT}} $$ ) and the stance times of each side were averaged over each distance. In the curve, the time to cover the 40-m sprint was longer than in the straight (5.52 ± 0.25 vs. 5.47 ± 0.23 s, respectively). Additionally, the left and the rightF A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ andIMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ were lower than in the straight while the left and the rightF M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ increased, meaning that theF M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ was more medial. The leftF V $$ {F}_{\mathrm{V}} $$ was also lower than in the straight while the left stance times increased to keep the leftIMP V $$ {IMP}_{\mathrm{V}} $$ similar to the straight to maintain the subsequent swing time. Overall, the sprinting performance was reduced in the curve due to a reduction in the left and the rightF A - P $$ {F}_{\mathrm{A}-\mathrm{P}} $$ andIMP A - P $$ {IMP}_{\mathrm{A}-\mathrm{P}} $$ , that were likely attributed to the concomitant increasedF M - L $$ {F}_{\mathrm{M}-\mathrm{L}} $$ to adopt a curvilinear motion.

Maximum velocity and leg-specific ground reaction force production change with radius during flat curve sprinting

Humans attain slower maximum velocity (vmax) on curves versus straight paths, potentially due to centripetal ground reaction force (GRF) production, and this depends on curve radius. Previous studies found GRF production differences between an athlete's inside versus outside leg relative to the center of the curve. Further, sprinting clockwise (CW) versus counterclockwise (CCW) slows vmax. We determined vmax, step kinematics and individual leg GRF on a straight path and on curves with 17.2 and 36.5 m radii for nine (8 male, 1 female) competitive sprinters running CW and CCW and compared vmax with three predictive models. We combined CW and CCW directions and found that vmax slowed by 10.0±2.4% and 4.1±1.6% (P<0.001) for the 17.2 and 36.5 m radius curves versus the straight path, respectively. vmax values from the predictive models were up to 3.5% faster than the experimental data. Contact length was 0.02 m shorter and stance average resultant GRF was 0.10 body weights (BW) greater for the 36.5 versus 17.2 m radius curves (P<0.001). Stance average centripetal GRF was 0.10 BW greater for the inside versus outside leg (P<0.001) on the 36.5 m radius curve. Stance average vertical GRF was 0.21 BW (P<0.001) and 0.10 BW (P=0.001) lower for the inside versus outside leg for the 17.2 and 36.5 m radius curves, respectively. For a given curve radius, vmax was 1.6% faster in the CCW compared with CW direction (P=0.003). Overall, we found that sprinters change contact length and modulate GRFs produced by their inside and outside legs as curve radius decreases, potentially limiting vmax.

Constant low-to-moderate mechanical asymmetries during 800-m track running

Introduction

Modifications in asymmetry in response to self-paced efforts have not been thoroughly documented, particularly regarding horizontally-derived ground reaction force variables. We determined the magnitude and range of gait asymmetries during 800 m track running.

Methods

Eighteen physical education students completed an 800 m self-paced run on a 200 m indoor track. During the run, vertical and horizontal ground reaction forces were measured at a sampling frequency of 500 Hz using a 5 m-long force platform system, with data collected once per lap. The following mechanical variables were determined for two consecutive steps: contact time and duration of braking/push-off phases along with vertical/braking/push-off peak forces and impulses. The group mean asymmetry scores were evaluated using the "symmetry angle" (SA) formula, where scores of 0% and 100% correspond to perfect symmetry and perfect asymmetry, respectively.

Results

There was no influence of distance interval on SA scores for any of the nine biomechanical variables (P ≥ 0.095). The SA scores were ∼1%-2% for contact time (1.3 ± 0.5%), peak vertical forces (1.8 ± 0.9%), and vertical impulse (1.7 ± 1.0%). The SA scores were ∼3%-8% for duration of braking (3.6 ± 1.1%) and push-off (3.2 ± 1.4%) phases, peak braking (5.0 ± 2.1%) and push-off (6.9 ± 3.1%) forces as well as braking (7.6 ± 2.3%) and push-off (7.7 ± 3.3%) impulses. The running velocity progressively decreased at 300 m and 500 m compared to that at 100 m but levelled off at 700 m (P < 0.001).

Discussion

There were no modifications in gait asymmetries, as measured at 200-m distance intervals during 800-m track running in physical education students. The 800 m self-paced run did not impose greater mechanical constraints on one side of the body. Experimental procedures for characterizing the gait pattern during 800 m track running could be simplified by collecting leg mechanical data from only one side.

Does lateral banking and radius affect well-trained sprinters and team-sports players during bend sprinting?

This study investigated the short-term responses of step characteristics in sprinters and team-sports players under different bend conditions. Eight participants from each group completed 80 m sprints in four conditions: banked and flat, in lanes two and four (L2B, L4B, L2F, L4F). Groups showed similar changes in step velocity (SV) across conditions and limbs. However, sprinters produced significantly shorter ground contact times (GCT) than team sports players in L2B and L4B for both left (0.123 s vs 0.145 s and 0.123 s vs 0.140 s) and right steps (0.115 s vs 0.136 s and 0.120 s vs 0.141 s) (p > 0.001-0.029; ES = 1.15-1.37). Across both groups, SV was generally lower in flat conditions compared to banked (Left: 7.21 m/s vs 6.82 m/s and Right: 7.31 m/s vs 7.09 m/s in lane two), occurring due to reduced step length (SL) rather than step frequency (SF), suggesting that banking improves SV via increased SL. Sprinters produced significantly shorter GCT in banked conditions that led to non-significant increases in SF and SV, highlighting the importance of bend sprinting specific conditioning and training environments representative of indoor competition for sprint athletes.

Interrelationships Between Multiple Speed Tests in Youth Soccer: Are Players Equally Efficient at Performing Different Sprint and Change of Direction Tasks?

ABSTRACT

Freitas, TT, Pereira, LA, Alcaraz, PE, Cadore, EL, Grazioli, R, Azevedo, PHSM, Jeffreys, I, and Loturco, I. Interrelationships between multiple speed tests in youth soccer: Are players equally efficient at performing different sprint and COD tasks? J Strength Cond Res 37(4): 848-853, 2023-We investigated the relationships between linear and multidirectional sprint tests in elite young soccer players, using different speed measurements and their associated deficits. Twenty-three under-17 and 17 under-16 soccer players performed, on the same day, 17-m linear sprint (with 10-m split times), curve sprints for "good" and "weak" sides (CSGS and CSWS, respectively), and zigzag and 505 change of direction (COD) tests. The Pearson's product moment test was used to determine the relationships among the tested variables. Significance level was set at p < 0.05. Large and very large significant correlations were observed between CSGS and CSWS and 10-m ( r = 0.73 and r = 0.53, respectively; p < 0.0001) and 17-m sprint velocity ( r = 0.84 and r = 0.74, respectively; p < 0.0001). Moderate and significant associations were identified between zigzag and 17-m sprint performances ( r = 0.40; p = 0.02). No significant relationships were found between 505 performance and 17-m sprint velocity and between the different COD tasks ( p > 0.05). Significant correlations were observed between sprint performance at 10- and 17-m and both CS and COD deficits ( r values ranging from 0.37 to 0.54; p < 0.05). In general, higher linear sprinting velocities were associated with superior performances in smoother multidirectional tasks (i.e., CS and zigzag tests) but not in more aggressive COD maneuvers (i.e., 505). Faster athletes in linear actions presented greater CS and COD deficits. No associations were detected between the different COD measurements, supporting the notion that the technical and mechanical demands of COD actions are angle and velocity dependent. From a practical perspective, comprehensive speed testing batteries (i.e., incorporating linear sprints, CS, and different COD assessments) should be administered to young soccer players, to better understand their ability to change direction and sprint over multiple trajectories.

Center of mass velocity comparison using a whole body magnetic inertial measurement unit system and force platforms in well trained sprinters in straight-line and curve sprinting

BACKGROUND

Sprint performance can be characterized through the centre of mass (COM) velocity over time. In-field computation of the COM is key in sprint training.

RESEARCH QUESTION

To compare the stance-averaged COM velocity computation from a Magneto-Inertial Measurement Units (MIMU) to a reference system: force platforms (FP), over the early acceleration phase in both straight and curve sprinting.

METHODS

Nineteen experienced-to-elite track sprinters performed 1 maximal sprint on both the straight and the curve (radius = 41.58 m) in a randomized order. Utilizing a MIMU-based system (Xsens MVN Link) and compared to FP (Kistler), COM velocity was computed with both systems. Averaged stance-by-stance COM velocity over straight-line and curve sprinting following the vertical axis (respectively V_zMIMU and V_zFP) and the norm of the two axes lying on the horizontal plane: x and y, approximately anteroposterior and mediolateral (respectively V_xyMIMU and V_xyFP) over the starting-blocks (SB) and initial acceleration (IA - composed out of the first four stances following the SB) were compared using mean bias, 95 % limits of agreements and Pearson's correlation coefficients.

RESULTS

148 stances were analyzed. V_xyMIMU mean bias was comprised between 0.26 % and 2.03 % (expressed in % with respect to the FP) for SB, 5.63 % and 7.29 % over IA respectively on the straight and the curve. Pearson's correlation coefficients ranged between 0.943 and 0.990 for V_xy, 0.423 and 0.938 for V_z. On the other hand, V_zMIMU mean bias ranged between 2.33 % and 4.69 % for SB, between 1.44 % and 19.95 % over IA respectively on the straight and the curve SIGNIFICANCE: The present findings suggest that the MIMU-based system tested slightly underestimated V_xyMIMU, though within narrow limits which supports its utilization. On the other hand, V_zMIMU computation in sprint running is not fully mature yet. Therefore, this MIMU-based system represents an interesting device for in-fieldV_xyMIMU computation either for straight-line and curve sprinting.

Sprinting with prosthetic versus biological legs: insight from experimental data

Running-prostheses have enabled exceptional athletes with bilateral leg amputations to surpass Olympic 400 m athletics qualifying standards. Due to the world-class performances and relatively fast race finishes of these athletes, many people assume that running-prostheses provide users an unfair advantage over biologically legged competitors during long sprint races. These assumptions have led athletics governing bodies to prohibit the use of running-prostheses in sanctioned non-amputee (NA) competitions, such as at the Olympics. However, here we show that no athlete with bilateral leg amputations using running-prostheses, including the fastest such athlete, exhibits a single 400 m running performance metric that is better than those achieved by NA athletes. Specifically, the best experimentally measured maximum running velocity and sprint endurance profile of athletes with prosthetic legs are similar to, but not better than those of NA athletes. Further, the best experimentally measured initial race acceleration (from 0 to 20 m), maximum velocity around curves, and velocity at aerobic capacity of athletes with prosthetic legs were 40%, 1-3% and 19% slower compared to NA athletes, respectively. Therefore, based on these 400 m performance metrics, use of prosthetic legs during 400 m running races is not unequivocally advantageous compared to the use of biological legs.

Evaluation of Lower Limb Muscle Electromyographic Activity during 400 m Indoor Sprinting among Elite Female Athletes: A Cross-Sectional Study

The purpose of this cross-sectional study was to analyze changes in normalized surface electromyography (sEMG) signals for the gastrocnemius medialis, biceps femoris, gluteus maximus, tibialis anterior, and vastus lateralis muscles occurring during a 400 m indoor sprint between subsequent curved sections of the track. Ten well-trained female sprinters (age: 21 ± 4 years; body mass: 47 ± 5 kg; body height: 161 ± 7 cm; 400 m personal best: 52.4 ± 1.1 s) performed an all-out 400 m indoor sprint. Normalized sEMG signals were recorded bilaterally from the selected lower limb muscles. The two-way ANOVA (curve × side) revealed no statistically significant interaction. However, the main effect analysis showed that normalized sEMG signals significantly increased in subsequent curves run for all the studied muscles: gastrocnemius medialis (p = 0.003), biceps femoris (p < 0.0001), gluteus maximus (p = 0.044), tibialis anterior (p = 0.001), and vastus lateralis (p = 0.023), but differences between limbs were significant only for the gastrocnemius medialis (p = 0.012). The results suggest that the normalized sEMG signals for the lower limb muscles increased in successive curves during the 400 m indoor sprint. Moreover, the gastrocnemius medialis of the inner leg is highly activated while running curves; therefore, it should be properly prepared for high demands, and attention should be paid to the possibility of the occurrence of a negative adaptation, such as asymmetries.

Comparison of Muscle Activity During 200 m Indoor Curve and Straight Sprinting in Elite Female Sprinters

The purpose of this study was to assess whether peak surface electromyography (sEMG) amplitude of selected lower limb muscles differed during a) curve and straight sprinting, b) sprinting in inside and outside lanes between lower limbs. Eleven well-trained female sprinters (personal best: 24.1 ± 1.1 s) were included in a randomized within-subject design study, in which participants underwent two experimental conditions: all-out 200 m indoor sprints in the innermost and outermost lane. Peak sEMG amplitude was recorded bilaterally from gastrocnemius medialis, biceps femoris, gluteus maximus, tibialis anterior, and vastus lateralis muscles. Left gastrocnemius medialis peak sEMG amplitude was significantly higher than for the right leg muscle during curve (p = 0.011) and straight sprinting (p < 0.001) when sprinting in the inside lane, and also significantly higher when sprinting in the inside vs. outside lane for both curve and straight sprinting (p = 0.037 and p = 0.027, respectively). Moreover, left biceps femoris peak sEMG amplitude was significantly higher during straight sprinting in the inside vs. outside lane (p = 0.006). Furthermore, right and left vastus lateralis peak sEMG amplitude was significantly higher during curve sprinting in the inside lane (p = 0.001 and p = 0.004, respectively) and for the left leg muscle peak sEMG amplitude was significantly higher during curve compared to straight sprinting in the outside lane (p = 0.024). Results indicate that curve sprinting creates greater demands mainly for the gastrocnemius medialis of the inner than the outer leg, but the degree of these requirements seems to depend on the radius of the curve, thus significant changes were noted during sprinting in the inside lane, but not in the outside lane.

The Symmetry of Fatigue of Lower Limb Muscles in 400 m Run Based on Electromyography Signals

Background: This study assesses curved track effects on fatigue symmetry and lower limb muscle activity while taking maximum velocity running kinematics into account. Methods: Polish master class athletes were examined (age 24.6 ± 3.67 years, bm 78.9 ± 6.02 kg, and bh 186.1 ± 6.63 cm). The measurements were made on a 400 m synthetic surface athletics track. The DelSys 16 channel system was employed to measure the activity of the right and left leg muscles. The kinematic variables of the run were obtained using a 3-axis accelerometer built into the recorder. Results: The study revealed curved track effects on asymmetric muscle activity and running kinematics in the first two sections of the run. On the first curve, the symmetry index (SI) was 8.1%, while in on straight, it was 11.5%. Moreover, significantly lower values of the fatigue index b were found for the right limb (F(3.36) = 6.504; p = 0.0152). Conclusions: A reduction of asymmetric muscle activity is linked with compensatory muscle stimulation triggered by the nervous system and with adjusting running kinematics to changing external conditions. Therefore, the main focus further research should be on the optimal interaction between stride length and frequency in relation to the muscle activity corresponding to the track geometry.

Evaluation of selected indices of gait asymmetry for the assessment of running asymmetry

BACKGROUND

The methods of running asymmetry evaluation are not as highly developed as the methods of gait evaluation.

RESEARCH QUESTION

Which asymmetry indices used in the gait analysis best characterize the asymmetry of the running movement?

METHODS

The kinematics of the sprint in a straight run over a distance of 50 m was evaluated using the X-sens system. Three indices (Ia, IS, SA) were based on discrete values from the first point of contact of the foot with the ground (1% of the running cycle phase) and were called discrete coefficients. Furthermore, two indices (SI, RAI) were used to evaluate asymmetry over the entire running cycle and were termed continuous coefficients. The study examined 21 elite and non-professional middle-distance runners of both sexes. The evaluation of the usefulness of individual indices for the evaluation of gait asymmetry was performed by means of the analysis of ROC curves and evaluation of data scatter on Bland-Altman charts.

RESULTS

The values of discrete and continuous asymmetry coefficients were different to each other. In Bland-Altman plots there was a meaningful variety of discrete coefficients and a small variety of continuous coefficients. The analysis of ROC curves proves this assumption. Including the real curve course of angular placement in particular joints it is observed that continuous coefficients describe asymmetry of movement more precisely.

SIGNIFICANCE

It was found that the so-called continuous indices SI and RAI ensure the best identification of the phenomenon of movement asymmetry.

Curve Sprint in Elite Female Soccer Players: Relationship with Linear Sprint and Jump Performance

The aim of this study was to examine the associations between linear sprint, curve sprint (CS), change of direction (COD) speed, and jump performance in a sample of 17 professional female soccer players. All athletes performed squat and countermovement jumps, single leg horizontal triple jumps, 17 m linear sprints, CS tests, and a 17 m Zigzag COD test. A Pearson product–moment test was performed to determine the relationships among the assessed variables. The significance level was set at p < 0.05. Nearly perfect associations (r > 0.9) were found between linear and CS velocities. Players faster in linear sprints and CS exhibited greater COD deficits. No significant associations were found between COD deficit and either body mass or sprint momentum. Jumping ability was significantly correlated with linear sprint and CS performance, but not to COD performance. These findings may be used by coaches and practitioners to guide testing and training prescriptions in this population. The associations observed here suggest that training methods designed to improve linear sprint and CS velocities may benefit from the implementation of vertically and horizontally oriented plyometric exercises.

Multidirectional sprints in soccer: are there connections between linear, curved, and change-of-direction speed performances?

BACKGROUND

The aim of this study was to investigate the relationships between linear sprint, curve sprint (CS) and change of direction (COD) abilities and vertical jump performance in elite young soccer players.

METHODS

Twenty-nine players from the same soccer club participated in this study. On the same day, athletes performed countermovement jump (CMJ), 17-m linear sprint (with a 10-m split time), CS (for both sides) and COD tests. A Pearson product moment correlation was performed to determine the associations between the assessed variables. Significance level was set at P<0.05.

RESULTS

Linear sprint was significantly related to CS (r ranging from 0.67 and 0.76; P<0.05) but not to COD performance (r=0.23 and 0.33 for 10- and 17-m, respectively; P>0.05). CS ability (for both good and weak sides) was significantly associated with COD performance (r=0.60 and 0.54, respectively; P<0.05). CMJ height was significantly correlated with both linear and CS velocities (r varying between 0.50 and 0.68; P<0.05), but not with COD velocity (r=0.37; P>0.05).

CONCLUSIONS

Based on these findings, it is possible to suggest that training strategies designed to improve vertical jumping capacity may potentially improve both linear and curvilinear sprint abilities. Moreover, increases in COD velocity may also produce positive changes in CS performance.

Curve sprinting in soccer: relationship with linear sprints and vertical jump performance

We examined the relationships among linear speed, vertical jumping ability and curve sprint (CS) performance. Moreover, the correlations between linear and curvilinear sprint velocities and CS deficit were tested. Twenty-eight under-20 soccer players performed squat and countermovement jumps, 17-m linear sprint (with split times at 5 and 10 m), and a CS test for both sides. For the first time, the new proposed CS deficit was calculated as the difference between 17-m velocity and CS test velocity. Pearson’s product moment of correlation was performed to determine the relationships among the distinct variables tested. Significance level was set at P < 0.05. Large to very large relationships between linear sprint speed and CS performance were observed, on both the “good” and “weak” sides. In addition, moderate to large correlations between linear and curve sprint abilities and vertical jumps were found. Finally, the CS deficit was negatively associated with the CS good side performance. Linear sprint and CS velocities for both good and weak sides were closely related. The CS deficit was only related to the CS weak side performance, and the vertical jumping ability was significantly associated with both linear and curvilinear sprint velocities. The present results suggest that training methods capable of improving linear sprint and vertical jumping abilities may also improve CS performance.

Influence of playing position and laterality in centripetal force and changes of direction in elite soccer players

The purpose of the present study was to: (a) assess centripetal force (CentF) and changes of direction (COD) in elite soccer players according to playing position (central defender, CD; lateral defender, LD; central midfielder, CM; lateral midfielder, LM; forward, FW), laterality (right-footed vs. left-footed) and field zone (central vs. lateral), and (b) analyze the relationship between anthropometric characteristics (age, weight, height, body mass and fat mass) and non-linear locomotion workload. Thirty professional soccer players (age: 26.57±5.56 years) were tracked during the 2017–2018 season during friendly, national and international matches (38 total games) using inertial measurement devices. CentF and COD were the variables extracted for analysis. A one-way ANOVA was used for playing position comparison, a t-test for laterality and field zone, and Pearson’s correlation coefficient to analyze relationships between anthropometric characteristics and dependent variables. There were differences by playing position in COD (556.33-to-412.18), R₂₀COD (484.36-to-354.81) and R₆₀COD (48.38-to-38.61) (p < .01; ω_p² = 0.03-to-0.05; CD>CM>LD>LM = FW); in COD_HIA (49.75-to-37.11), R₂₀COD_HIA (16.04-to-9.11) and R₆₀COD_HIA (10.64-to-9.11) (p < .01; ω_p² = 0.03-to-0.07; CM>FW>LM>CD = LD); in COD_SPRINT (14.56-to-8.40) and R₂₀COD_SPRINT (3.29-to-1.40) (p < .01; ω_p² = 0.03-to-0.04; FW = LM = CM>CD = LD); and in CentF_MAX both in clockwise (992.04-to-902.09N) and counterclockwise (999.24-to-872.61N) directions (p < .02; ω_p² = 0.02-to-0.07; FW = CD>CM = LM = LD). The highest values of counterclockwise CentF were performed by left-footed players in the central zone (p < .001; d = 0.71-to-1.44) and clockwise CentF by right-footed players (p < .001; d = 0.04-to-0.55) in the lateral field zone. Moderate correlations were found between age, body mass and high intensity/sprints COD and repeated COD ability (p < .05; r = 0.235-to-0.383). Therefore, team staff should consider anthropometric characteristics, playing position, laterality and field zone to individualize training workload related to non-linear locomotion in soccer.

Joint moments and power in the acceleration phase of bend sprinting

Joint kinetics of the lower limb (hip, knee, ankle, midfoot and metatarsophalangeal joints) were investigated during the acceleration phase of bend sprinting and straight-line sprinting. Within the bend sprinting literature, it is generally accepted that sprint performance on the bend is restricted by moments in the non-sagittal plane preventing the production of force in the sagittal plane. However, there is limited evidence in conditions representative of elite athletics performance that supports this hypothesis. Three-dimensional kinematic and ground reaction force data were collected from seven participants during sprinting on the bend (36.5 m radius) and straight, allowing calculation of joint moment, power and energy. No changes in extensor moment were observed at the hip and knee joints. Large effect sizes (g = 1.07) suggest a trend towards an increase in left step peak ankle plantarflexion moment. This could be due to a greater need for stabilisation of the ankle joint as a consequence of non-sagittal plane adaptations of the lower limb. In addition, the observed increase in peak MTP joint plantar-flexor moment might have implications for injury risk of the fifth metatarsal. Energy generation, indicated by positive power, in the sagittal plane at the MTP and ankle joints was moderately lower on the bend than straight, whilst increases in non-sagittal plane energy absorption were observed at the ankle joint. Therefore, energy absorption at the foot and ankle may be a key consideration in improving bend sprinting performance.

Influence of Contextual Variables in the Changes of Direction and Centripetal Force Generated during an Elite-Level Soccer Team Season

The study of the contextual variables that affect soccer performance is important to be able to reproduce the competition context during the training sessions. Therefore, the aim of the present study was to evaluate the effect of match outcome as related to goal difference (large win, >2 goals, LW; narrow win, 1–2 goals, NW; drawing, D; narrow loss, 1–2 goals, NL; or large loss, >2 goals, LL), match location (home, H; away, A; neutral, N), type of competition (international, INT; national, NAT; friendly, F), phase of the season (summer preseason, SPS; in-season 1, IS1; winter preseason, WPS; in-season 2), and the field surface (natural grass, NG; artificial turf, TF) on the change of direction (COD) and centripetal force (CentF) generated during official games. Thirty male elite-level soccer players (age: 26.57 ± 5.56 years) were assessed while using WIMU PRO^TM inertial devices (RealTrack Systems, Almeria, Spain) in 38 matches during the 2017–2018 season, selecting for analysis the number of COD at different intensities and the CentF, depending on the turn direction. Statistical analyses comprised a one-way ANOVA with the Bonferroni post-hoc and t-test for independent samples. The main results showed that the match outcome (ω_p² = 0.01–0.04; NW = D = NL > LL), match location (ω_p² = 0.01–0.06; A = N > H), type of competition (ω_p² = 0.01–0.02; INT > NAT > F), and period of the season (ω_p² = 0.01–0.02; SPS = IS1 = WPS > IS2) all exert some influence. No effect was found for the playing surface. Therefore, match outcome, match location, type of competition, and period of the season influence the demands of centripetal force and changes of direction. These aspects should be considered in the design of training sessions and microcycle workload planning during the season to improve competitive success.

Kinematic modifications of the lower limb during the acceleration phase of bend sprinting

A decrease in speed when sprinting on the bend compared with the straight has been attributed to kinetic, kinematic and spatiotemporal modifications. Although maximal speed is dependent on an athlete's ability to accelerate, there is limited research investigating the acceleration phase of bend sprinting. This study used a lower limb and trunk marker set with 15 optoelectronic cameras to examine kinematic and spatiotemporal variables of the lower limb during sprinting on the bend and straight. Nine sprinters completed up to six 30 m maximal effort trials in bend (radius 36.5 m, lane one) and straight conditions. An increase in body lateral lean at touchdown resulted in a number of asymmetric kinematic modifications. Whilst the left limb demonstrated a greater peak hip adduction, peak hip internal rotation and peak ankle eversion on the bend compared with the straight, the right limb was characterised by an increase in peak hip abduction. These results demonstrate that kinematic modifications start early in the race and likely accumulate, resulting in greater modifications at maximal speed. It is recommended that strength and conditioning programmes target the hip, ankle and foot in the non-sagittal planes. In addition, sprint training should prioritise specificity by occurring on the bend.

Hamstring rehabilitation in elite track and field athletes: applying the British Athletics Muscle Injury Classification in clinical practice

Rationale

Hamstring injuries are common in elite sports. Muscle injury classification systems aim to provide a framework for diagnosis. The British Athletics Muscle Injury Classification (BAMIC) describes an MRI classification system with clearly defined, anatomically focused classes based on the site of injury: (a) myofascial, (b) muscle–tendon junction or (c) intratendinous; and the extent of the injury, graded from 0 to 4. However, there are no clinical guidelines that link the specific diagnosis (as above) with a focused rehabilitation plan.

Objective

We present an overview of the general principles of, and rationale for, exercise-based hamstring injury rehabilitation in British Athletics. We describe how British Athletics clinicians use the BAMIC to help manage elite track and field athletes with hamstring injury. Within each class of injury, we discuss four topics: clinical presentation, healing physiology, how we prescribe and progress rehabilitation and how we make the shared decision to return to full training. We recommend a structured and targeted diagnostic and rehabilitation approach to improve outcomes after hamstring injury.

Measurement of bend sprinting kinematics with three-dimensional motion capture: a test-retest reliability study

Sprint velocity decreases on the bend when compared with the straight, therefore understanding technique during bend sprinting could have important implications for aiding race performance. Few bend sprinting studies have used optoelectronic cameras to investigate kinematic variables. Limited published evidence regarding the reliability of marker sets in conditions representative of elite bend sprinting makes model selection difficult. Therefore, a test-retest protocol was conducted to establish the reliability and minimum detectable difference of a lower limb and trunk marker set during bend sprinting (radius: 36.5 m). Six participants completed five, 60 m trials at maximum effort, with data collected at 38-45 m. This was repeated 2-7 days later. Spatio-temporal (e.g., contact time) and kinematic variables (e.g., peak joint angles) were evaluated. Intra-class correlation coefficients (ICC) were used to determine the between- and within-day reliability. Between-day reliability (ICC 3, k) was fair to excellent for all variables. Compared to between-day, within-day reliability demonstrated stronger agreement for the majority of variables. Thus, same-day data collection is preferable. It has been established that the marker set is reliable for future use. In addition, the minimal detectable difference was calculated which serves as useful reference for future research in bend sprinting.

How to Maintain Maximal Straight Path Running Speed on a Curved Path in Sprint Events

This study aims to clarify the ideal technique for running on a curved path during sprinting events. Participants were twelve male track and field athletes including long jumpers and sprinters. The participants performed a 60-m sprint with maximal effort on straight and curved paths. Participants were divided into "good curve runners" and "poor curve runners" according to the curved path running speed relative to that of the straight path. Kinematic variables and ground reaction forces (GRFs) were registered and compared between the groups and paths. The running speed, step length, and flight distance of the outside leg on the curved path were lower than on the straight path only in poor curve runners. The medial-lateral GRF and impulse showed an increase during curved path running for both groups. However, the maximum posterior GRF and impulse decreased only in poor curve runners. The ideal technique for running on a curved path is to maintain the same kinematics and kinetics in the sagittal plane as on a straight path.

A Review of the Evolution of Vision-Based Motion Analysis and the Integration of Advanced Computer Vision Methods Towards Developing a Markerless System

BACKGROUND

The study of human movement within sports biomechanics and rehabilitation settings has made considerable progress over recent decades. However, developing a motion analysis system that collects accurate kinematic data in a timely, unobtrusive and externally valid manner remains an open challenge.

MAIN BODY

This narrative review considers the evolution of methods for extracting kinematic information from images, observing how technology has progressed from laborious manual approaches to optoelectronic marker-based systems. The motion analysis systems which are currently most widely used in sports biomechanics and rehabilitation do not allow kinematic data to be collected automatically without the attachment of markers, controlled conditions and/or extensive processing times. These limitations can obstruct the routine use of motion capture in normal training or rehabilitation environments, and there is a clear desire for the development of automatic markerless systems. Such technology is emerging, often driven by the needs of the entertainment industry, and utilising many of the latest trends in computer vision and machine learning. However, the accuracy and practicality of these systems has yet to be fully scrutinised, meaning such markerless systems are not currently in widespread use within biomechanics.

CONCLUSIONS

This review aims to introduce the key state-of-the-art in markerless motion capture research from computer vision that is likely to have a future impact in biomechanics, while considering the challenges with accuracy and robustness that are yet to be addressed.

Bend sprinting performance: new insights into the effect of running lane

Athletes in inner lanes may be disadvantaged during athletic sprint races containing a bend portion because of the tightness of the bend. We empirically investigated the veracity of modelled estimates of this disadvantage and the effect of running lane on selected kinematic variables. Three-dimensional video analysis was conducted on nine male athletes in lanes 8, 5 and 2 of the bend of an outdoor track (radii: 45.10, 41.41 and 37.72 m, respectively). There was over 2% (p < 0.05) reduction in mean race velocity from lane 8 (left step 9.56 ± 0.43 m/s, right step: 9.49 ± 0.41 m/s) to lane 5 (left step: 9.36 ± 0.51 m/s, right step: 9.30 ± 0.51 m/s), with only slight further reductions from lane 5 to lane 2 (left step: 9.34 ± 0.61 m/s, right step: 9.30 ± 0.63 m/s). Race velocity decreased mainly because of reductions in step frequency as radius decreased. These unique data demonstrate the extent of the disadvantage of inner lane allocation during competition may be greater than previously suspected. Variations in race velocity changes might indicate some athletes are better able to accommodate running at tighter radii than others, which should have implications for athletes' training.

Leg amputation side determines performance in curve sprinting: a case study on a Paralympic medalist

The lower limb kinetics of curve sprinting in amputees are not well described in the literature, particularly with respect to the effect of the side of amputation. This is an issue due to the importance of the knowledge for prosthetic design and classification of athletes. Thus, the aim of this study was to investigate the influence of side of amputation on curve sprinting performance in athletes with a unilateral leg amputation. A three-dimensional motion analysis system (Vicon), four force plates (Kistler) and a modified mathematical human model (ALASKA) were used to compare clockwise and counter clockwise curve sprinting lower limb kinematics and kinetics of a Paralympic medalist with a left-sided knee exarticular amputation. Results reveal that vertical ground reaction force application and total vertical impulse were lower when the affected limb was at the inside of the curve. The unaffected limb showed joint mechanics different to those established for non-amputee athletes and might contribute better to propulsion when being the inside limb. Curve sprinting biomechanics and the ability to attain high radial velocities are directly dependent on the side of amputation relative to the curve direction in a unilateral amputee athlete of highest performance level.

Relationship between lateral differences in the cross-sectional area of the psoas muscle and curve running time

BACKGROUND

The aim of this study was to investigate whether lateral differences in the cross-sectional areas of the hip and thigh muscles were related to curve sprinting time.

METHODS

Thirteen college students (10 men and 3 women; mean ± SD: age, 20.4 ± 1.7 years; height, 167.6 ± 8.9 cm; mass, 57.4 ± 5.4 kg) participated in this study. The participants were instructed to sprint along a circular track (23 m radius) in the counterclockwise and clockwise directions. Magnetic resonance imaging was used to measure the cross-sectional area of the psoas major, quadriceps femoris, and hamstring muscles. The symmetry index was used to evaluate the lateral differences in the cross-sectional area.

RESULTS

The lateral difference was observed in the cross-sectional area (CSA) of the thigh muscles, not in the psoas major muscle. The sprint time was not significantly different between the counterclockwise (22.15 ± 2.27 s) and clockwise (22.13 ± 2.32 s) directions. No significant correlations were found between the symmetry index of the thigh muscles and the cross-directional differences in sprint time. However, the symmetry index of the psoas major muscle correlated significantly with the cross-directional difference in sprint time (r = -0.614, P = 0.026).

CONCLUSIONS

These findings suggest that the participants in whom the cross-sectional area of the psoas major muscle of the outer leg was larger than that of the inner leg were faster in curve sprinting.

Force production during maximal effort bend sprinting: Theory vs reality

This study investigated whether the "constant limb force" hypothesis can be applied to bend sprinting on an athletics track and to understand how force production influences performance on the bend compared with the straight. Force and three-dimensional video analyses were conducted on seven competitive athletes during maximal effort sprinting on the bend (radius 37.72 m) and straight. Left step mean peak vertical and resultant force decreased significantly by 0.37 body weight (BW) and 0.21 BW, respectively, on the bend compared with the straight. Right step force production was not compromised in the same way, and some athletes demonstrated substantial increases in these variables on the bend. More inward impulse during left (39.9 ± 6.5 Ns) than right foot contact (24.7 ± 5.8 Ns) resulted in 1.6° more turning during the left step on the bend. There was a 2.3% decrease in velocity from straight to bend for both steps. The constant limb force hypothesis is not entirely valid for maximal effort sprinting on the bend. Also, the force requirements of bend sprinting are considerably different to straight-line sprinting and are asymmetrical in nature. Overall, bend-specific strength and technique training may improve performance during this portion of 200- and 400-m races.