The effect of a reduced first step width on starting block and first stance power and impulses during an athletic sprint start

This study investigated how manipulating first step width affects 3D external force production, centre of mass (CoM) motion and performance in athletic sprinting. Eight male and 2 female competitive sprinters (100m PB: 11.03 ± 0.36 s male and 11.6 ± 0.45 s female) performed 10 maximal effort block starts. External force and three-dimensional kinematics were recorded in both the block and first stance phases. Five trials were performed with the athletes performing their preferred technique (Skating) and five trials with the athletes running inside a 0.3 m lane (Narrow). By reducing step width from a mean of 0.31 ± 0.06 m (Skating) to 0.19 ± 0.03 m (Narrow), reductions were found between the two styles in medial block and medial 1st stance impulses, 1st stance anterior toe-off velocity and mediolateral motion of the CoM. No differences were found in block time, step length, stance time, average net resultant force vector, net anteroposterior impulse nor normalised external power. Step width correlated positively with medial impulse but not with braking nor net anteroposterior impulse. Despite less medially directed forces and less mediolateral motion of the CoM in the Narrow trials, no immediate improvement to performance was found by restricting step width.     

Three-dimensional CoM energetics,pelvis and lower limbs joint kinematics of uphill treadmill running at high speed

ABSTRACT

The purpose of this study was to investigate the effects of slope on three-dimensional running kinematics at high speed. Thirteen male sprinters ran at high speed (7.5 m/s) on a motorised treadmill in each a level and a 5.0% slope condition. Three-dimensional motion analysis was conducted to compare centre of mass (CoM) energetics, pelvis segment and lower limb joints kinematics. We found that contact time was not affected by the slope, whereas flight time and step length were significantly shorter in uphill compared to level running. Uphill running reduced negative CoM work and increased positive CoM work compared to level running. Ankle, knee and hip joints were more flexed at initial ground contact, but only the knee was more extended at the end of stance in uphill compared to level running. Additionally, the hip joint was more abducted, and the free leg side of the pelvis was more elevated at the end of stance in uphill running. Our results demonstrate that joint motion must be developed from a more flexed/adducted position at initial contact through a greater range of motion compared to level running in order to meet the greater positive CoM work requirements in uphill running at high speed.     

Primary mechanical factors contributing to foot eversion moment during the stance phase of running

Rearfoot external eversion moments due to ground reaction forces (GRF) during running have been suggested to contribute to overuse running injuries. This study aimed to identify primary factors inducing these rearfoot external eversion moments. Fourteen healthy men ran barefoot across a force plate embedded in the middle of 30-m runway with 3.30 ± 0.17 m · s^–1. Total rearfoot external eversion/inversion moments (Mtot) were broken down into the component Mxy due to medio-lateral GRF (Fxy) and the component Mz due to vertical GRF (Fz). Ankle joint centre height and medio-lateral distance from the centre of pressure to the ankle joint centre (a_cop) were calculated as the moment arm of these moments. Mxy dominated Mtot just after heel contact, with the magnitude strongly dependent on Fxy, which was most likely caused by the medio-lateral foot velocity before heel contact. Mz then became the main generator of Mtot throughout the first half of the stance phase, during which a_cop was the critical factor influencing the magnitude. Medio-lateral foot velocity before heel contact and medio-lateral distance from the centre of pressure to the ankle joint centre throughout the first half of the stance phase were identified as primary factors inducing the rearfoot external eversion moment.     

The effect of alterations in foot centre of pressure on lower body kinematics during the five-iron golf swing

ABSTRACT

The research aimed to evaluate the effects of an intervention aimed at altering pressure towards the medial aspect of the foot relating to stability mechanisms associated with the golf swing. We hypothesised that by altering the position of the foot pressure, the lower body stabilisation would improve which in turn would enhance weight distribution and underpinning lower body joint kinematics. Eight professional golf association (PGA) golf coaches performed five golf swings, recorded using a nine-camera motion analysis system synchronised with two force platforms. Following verbal intervention, they performed further five swings. One participant returned following a one-year intervention programme and performed five additional golf swings to provide a longitudinal case study analysis. Golf performance was unchanged evidenced by the velocity and angle of the club at ball impact (BI), although the one-year intervention significantly changed the percentage of weight experienced at each foot in the final 9% of downswing, which provided an even weight distribution at BI. This is a highly relevant finding as it indicates that the foot centre of pressure was central to the base of support and in-line with the centre of mass (CoM), indicating significantly increased stability when the CoM is near maximal acceleration.     

Anticipation by basketball defenders: An explanation based on the three-dimensional inverted pendulum model

Abstract

We previously estimated the timing when ball game defenders detect relevant information through visual input for reacting to an attacker's running direction after a cutting manoeuvre, called cue timing. The purpose of this study was to investigate what specific information is relevant for defenders, and how defenders process this information to decide on their opponents' running direction. In this study, we hypothesised that defenders extract information regarding the position and velocity of the attackers' centre of mass (CoM) and the contact foot. We used a model which simulates the future trajectory of the opponent's CoM based upon an inverted pendulum movement. The hypothesis was tested by comparing observed defender's cue timing, model-estimated cue timing using the inverted pendulum model (IPM cue timing) and cue timing using only the current CoM position (CoM cue timing). The IPM cue timing was defined as the time when the simulated pendulum falls leftward or rightward given the initial values for position and velocity of the CoM and the contact foot at the time. The model-estimated IPM cue timing and the empirically observed defender's cue timing were comparable in median value and were significantly correlated, whereas the CoM cue timing was significantly more delayed than the IPM and the defender's cue timings. Based on these results, we discuss the possibility that defenders may be able to anticipate the future direction of an attacker by forwardly simulating inverted pendulum movement.     

The effects of an unanticipated side-cut on lower extremity kinematics and ground reaction forces during a drop landing

Unanticipated direction to cut after landing may alter the lower extremity landing biomechanics when performing landing motions. These alterations may potentially increase the risk of ACL injury. The purpose of this study was to determine if an unanticipated side-cut affects lower extremity landing biomechanics in females. Eighteen recreational female athletes participated in two blocks of testing: the first block of testing consisted of three acceptable trials of anticipated dominant limb and non-dominant limb 45-degree diagonal cutting after landing, which were performed in a counterbalanced order. The second block of testing consisted of three acceptable trials of unanticipated dominant limb and non-dominant limb diagonal cutting after landing. Data analysis mainly focused on the dominant limb landing biomechanics. Unanticipated side-cut landing, compared (paired t-test, p < 0.05) to the anticipated landings, resulted in less hip abduction and tibial internal rotation angle at initial contact (IC) and a lower maximum ankle inversion angle and a greater maximum knee abduction angle, and knee and hip displacement. Also, greater posterior GRF and a longer time to peak medial GRF were exhibited. These outcomes indicate that athletes may adapt their landing mechanics to land unsafely when encountering an unanticipated event.     

Effects of stance width on performance and postural stability in national-standard pistol shooters

Abstract

The aim of the present study was to determine whether changing stance width would result in a corresponding change in postural and/or pistol stability. Twelve national-standard male air pistol shooters performed 10 shots each at five stance widths (30 cm, 45 cm, 60 cm, 75 cm, and 90 cm). Postural stability was determined by measuring centre-of-pressure changes with a dual force-platform system. Shooting mechanics measures were determined by a NOPTEL ST-2000 optoelectronic training system. Medial-lateral centre-of-pressure excursion (F _4,44 = 7.17, P < 0.001, effect size = 0.99) and speed (F _4,44 = 77.03, P < 0.001, effect size = 3.88) were reduced as stance width decreased. Centre of gravity fine (the percentage of time held within an area the size of the ten-ring) improved during narrower stance widths (F _4,32 = 12.49, P < 0.001, effect size = 0.71). Our findings suggest that stance width affects postural and pistol stability in national-standard air pistol athletes. Moreover, the current method of suggesting a wider stance to improve shooting performance should be reconsidered and perhaps air-pistol shooters should use a 30-cm stance width to improve postural stability and shooting performance.     

Effect of custom-made and prefabricated insoles on plantar loading parameters during running with and without fatigue

Abstract

Controversy exists whether custom-made insoles are more effective in reducing plantar loading compared to prefabricated insoles. Forty recreational athletes ran using custom-made, prefabricated, and the original insoles of their running shoes, at rest and after a fatigue run. Contact time, stride rate, and plantar loading parameters were measured. Neither the insole conditions nor the fatigue state modified contact time and stride rate. Addressing prevention of running injuries, post-fatigue loading values are of great interest. Custom-made insoles reduced the post-fatigue loading under the hallux (92 vs. 130 kPa, P < 0.05), medial midfoot (70 vs. 105 kPa, P < 0.01), and lateral midfoot (62 vs 96 kPa, P < 0.01). Prefabricated insoles provoked reductions in post-fatigue loading under the toes (120 vs. 175 kPa, P < 0.05), medial midfoot (71 vs. 105 kPa, P < 0.01), and lateral midfoot (68 vs. 96 kPa, P < 0.01). Regarding both study insoles, custom-made insoles reduced by 31% and 54% plantar loading under the medial and lateral heel compared to the prefabricated insoles. Finally, fatigue state did not influence plantar loading regardless the insole condition. In long-distance races, even a slight reduction in plantar loading at each foot strike may suppose a significant decrease in the overall stress experienced by the foot, and therefore the use of insoles may be an important protective mechanism for plantar overloading.     

Understanding the effect of touchdown distance and ankle joint kinematics on sprint acceleration performance through computer simulation

This study determined the effects of simulated technique manipulations on early acceleration performance. A planar seven-segment angle-driven model was developed and quantitatively evaluated based on the agreement of its output to empirical data from an international-level male sprinter (100 m personal best = 10.28 s). The model was then applied to independently assess the effects of manipulating touchdown distance (horizontal distance between the foot and centre of mass) and range of ankle joint dorsiflexion during early stance on horizontal external power production during stance. The model matched the empirical data with a mean difference of 5.2%. When the foot was placed progressively further forward at touchdown, horizontal power production continually reduced. When the foot was placed further back, power production initially increased (a peak increase of 0.7% occurred at 0.02 m further back) but decreased as the foot continued to touchdown further back. When the range of dorsiflexion during early stance was reduced, exponential increases in performance were observed. Increasing negative touchdown distance directs the ground reaction force more horizontally; however, a limit to the associated performance benefit exists. Reducing dorsiflexion, which required achievable increases in the peak ankle plantar flexor moment, appears potentially beneficial for improving early acceleration performance.     

Stance limb kinetics of older male athletes endurance running performance

The aim of this study was to examine the age-based, lower limb kinetics of running performances of endurance athletes. Six running trials were performed by 24 male athletes, who were distinguished by three age groupings (S35: 26–32 years, M50: 50–54 years, M60+: 60–68 years). Lower limb coordinate and ground reaction force data were collected using a nine camera infra-red system synchronised with a force plate. A slower anteroposterior (M ± SD S35 = 4.13 ± 0.54 m/s: M60+ = 3.34 ± 0.40 m/s, p < 0.05) running velocity was associated with significant (p < 0.05) decreases in step length and discrete vertical ground contact force between M60+and S35 athletes. The M60+athletes simultaneously generated a 32% and 42% reduction (p < 0.05) in ankle joint moment when compared to the M50 and S35 athletes and 72% (p < 0.05) reduction in knee joint stiffness when compared to S35 athletes. Age-based declines in running performance were associated with reduced stance phase force tolerance and generation that may be accounted for due to an inhibited force–velocity muscular function of the lower limb. Joint-specific coaching strategies customised to athlete age are warranted to maintain/enhance athletes' dynamic performance.     

Ankle taping can reduce external ankle joint moments during drop landings on a tilted surface

Ankle taping is commonly used to prevent ankle sprains. However, kinematic assessments investigating the biomechanical effects of ankle taping have provided inconclusive results. This study aimed to determine the effect of ankle taping on the external ankle joint moments during a drop landing on a tilted surface at 25°. Twenty-five participants performed landings on a tilted force platform that caused ankle inversion with and without ankle taping. Landing kinematics were captured using a motion capture system. External ankle inversion moment, the angular impulse due to the medio-lateral and vertical components of ground reaction force (GRF) and their moment arm lengths about the ankle joint were analysed. The foot plantar inclination relative to the ground was assessed. In the taping condition, the foot plantar inclination and ankle inversion angular impulse were reduced significantly compared to that of the control. The only component of the external inversion moment to change significantly in the taped condition was a shortened medio-lateral GRF moment arm length. It can be assumed that the ankle taping altered the foot plantar inclination relative to the ground, thereby shortening the moment arm of medio-lateral GRF that resulted in the reduced ankle inversion angular impulse.     

Assessment of balance among adolescent track and field athletes

Track and field events place different demands on athletes and may have an effect on balance. This study investigated the effects of event specialty, gender, and leg dominance on balance among adolescent track and field athletes. Forty healthy adolescent track and field athletes (male = 23, female = 17) categorised into three different groups (sprinter = 20, distance runners = 13, throwers = 7) had their single leg static balance measured with the eyes open and the eyes closed using an AMTI force platform. Dependent variables included average displacement (cm) of the centre of pressure (COP) in the anterior/posterior direction and medial/lateral directions, the average velocity of the COP (cm/s) and the 95% ellipse area (cm²). Variables were analysed using a 3 (event specialty) × 2 (gender) × 2 (leg) ANOVA with repeated measures on the leg variable (p < 0.05). There was a significant difference (p < 0.05) in the average displacement of the COP in the medial/lateral direction for both the eyes open and closed condition, with the non-dominant leg demonstrating greater displacement than the dominant leg. This might increase the risk of injury for the non-dominant leg, but additional data should be collected and analysed on both dynamic balance and performance.     

Segment coupling and coordination variability analyses of the roundhouse kick in taekwondo relative to the initial stance position

The initial stance position (ISP) has been observed as a factor affecting the execution technique during taekwondo kicks. In the present study, authors aimed to analyse a roundhouse kick to the chest by measuring movement coordination and the variability of coordination and comparing this across the different ISP (0°, 45° and 90°). Eight experienced taekwondo athletes performed consecutive kicking trials in random order from every of the three relative positions. The execution was divided into three phases (stance, first swing and second swing phase). A motion capture system was used to measure athletes’ angular displacement of pelvis and thigh. A modified vector coding technique was used to quantify the coordination of the segments which contributed to the overall movement. The variability of this coordination (CV) for each ISP was also calculated. Comparative analysis showed that during the stance phase in the transverse plane, athletes coordinated movement of the trunk and thigh with a higher frequency of in-phase and lower frequency of exclusive thigh rotation in the 0° stance than the 90° stance position (P < 0.05). CV was also influenced by the different ISP. During the first swing and the majority of the second swing phase, predominant in-phase coordination of the pelvis and thigh was observed. Including exercises that require in-phase movement could not only help athletes to acquire coordination stability but also efficiency. The existence of a constraint such as ISP implies an increase of the variability when the athletes have to kick from ISP they are not used to adopt (i.e., 0° and 90° ISP) as an evidence of adaptability in the athletes’ execution technique.     

Lower limb joint kinetics in the starting blocks and first stance in athletic sprinting

The aim of this study was to examine lower limb joint kinetics during the block and first stance phases in athletic sprinting. Ten male sprinters (100 m PB, 10.50 ± 0.27 s) performed maximal sprint starts from blocks. External force (1000 Hz) and three-dimensional kinematics (250 Hz) were recorded in both the block (utilising instrumented starting blocks) and subsequent first stance phases. Ankle, knee and hip resultant joint moment, power and work were calculated at the rear and front leg during the block phase and during first stance using inverse dynamics. Significantly (P < 0.05) greater peak moment, power and work were evident at the knee joint in the front block and during stance compared with the rear block. Ankle joint kinetic data significantly increased during stance compared with the front and rear block. The hip joint dominated leg extensor energy generation in the block phase (rear leg, 61 ± 10%; front leg, 64 ± 8%) but significantly reduced during stance (32 ± 9%), where the ankle contributed most (42 ± 6%). The current study provides novel insight into sprint start biomechanics and the contribution of the lower limb joints towards leg extensor energy generation.     

Effects of stance width on performance and postural stability in national-standard pistol shooters

The aim of the present study was to determine whether changing stance width would result in a corresponding change in postural and/or pistol stability. Twelve national-standard male air pistol shooters performed 10 shots each at five stance widths (30 cm, 45 cm, 60 cm, 75 cm, and 90 cm). Postural stability was determined by measuring centre-of-pressure changes with a dual force-platform system. Shooting mechanics measures were determined by a NOPTEL ST-2000 optoelectronic training system. Medial-lateral centre-of-pressure excursion (F?,?? = 7.17, P < 0.001, effect size = 0.99) and speed (F?,?? = 77.03, P < 0.001, effect size = 3.88) were reduced as stance width decreased. Centre of gravity fine (the percentage of time held within an area the size of the ten-ring) improved during narrower stance widths (F?,?? = 12.49, P < 0.001, effect size = 0.71). Our findings suggest that stance width affects postural and pistol stability in national-standard air pistol athletes. Moreover, the current method of suggesting a wider stance to improve shooting performance should be reconsidered and perhaps air-pistol shooters should use a 30-cm stance width to improve postural stability and shooting performance.     

Athletics

The purpose of this study was to determine primary factors that contribute to the magnitude of the maximum torsional moment on the tibia during running based on information from three‐dimensional shank kinematics and ground reaction forces. Eight male subjects were asked to run along a straight track at 5.0 m s^‐1. Data were collected using two high‐speed cameras and a force platform. Each subject's left foot and tibia were modelled as a system of coupled rigid bodies. First, net axial moments acting at both ends of the tibia were calculated using inverse dynamics. Then the tibial torsional moment was determined from the quasi‐equilibrium balance of the net tibial axial moments. Our results showed considerable inter‐individual variations for the tibial torsional moment during the stance phase of running. The maximum torsional moment reflecting external rotational loading of the proximal tibia was significantly correlated with the outward tilt angle of the shank in the frontal plane (r = 0.78, p <0.05) and with the vertical force of ground reaction (r = 0.70, p <0.05). In conclusion, lowering tibial torsional loading by interventions based on the present findings may lead to the reduction of running injuries that occur in athletes’ tibiae.     

The role of the athletes’ entourage on attitudes to doping

ABSTRACT

The present study investigated athletes’ and coaches’ beliefs about the role of athletes’ entourage in deterring or promoting doping. Competitive athletes and coaches in Greece and Australia took part in semi-structured interviews. Our analysis of the interviews produced five main themes: coach influence, peer influence, doping stance, doping stigma, and entourage’s culture. Overall, coaches and peers having a close and trusty relationship with the athletes were considered most influential with respect to doping-related decisions. The majority of the athletes held a strong anti-doping stance but could not articulate why they held this position. This inability could be ascribed to the stigmatization of doping which led to lack of knowledge and anti-doping education. Finally, an anti-doping culture in the athletes’ environment was considered central to an anti-doping stance. The study findings provide valuable information towards a comprehensive understanding of the role athletes’ entourage can play in shaping athletes’ attitudes and decision for doping.     

Blocking landing techniques in volleyball and the possible association with anterior cruciate ligament injury

The number and type of landings performed after blocking during volleyball matches has been related to the potential risk of ACL injury. The aim of the present study was to determine whether gender affects the frequency of specific blocking landing techniques with potential risk of ACL injury from the perspective of foot contact and subsequent movement after the block used by volleyball players during competitive matches. Three matches involving four female volleyball teams (fourteen sets) and three matches involving four male volleyball teams (thirteen sets) in the Czech Republic were analyzed for this study. A Pearson chi-square test of independence was used to detect the relationship between gender and different blocking techniques. The results of the present study showed that gender affected single-leg landings with subsequent movement in lateral direction and double-leg landings. Although the total number of landings was lower for male athletes than for female athletes, a larger portion of male athletes demonstrated single leg landings with a subsequent movement than female athletes. Single leg landings with a subsequent movement have a higher potential risk of ACL injury.     

Different visual stimuli affect muscle activation at the knee during sidestepping

Increasing knee stability via appropriate muscle activation could reduce anterior cruciate ligament (ACL) injury risk during unplanned sidestepping. High-level athletes may activate their knee muscles differently from low-level athletes when responding to quasi-game realistic versus non game-realistic stimuli. Eleven high-level and 10 low-level soccer players responded to a non game-realistic arrow-planned condition (AP), a quasi game-realistic one-defender scenario (1DS) and two-defender scenario (2DS), and an arrow-unplanned condition (AUNP), that imposed increasing time constraints to sidestep. Activation from eight knee muscles during sidestepping was measured during pre-contact and weight-acceptance. Knee flexor-extensor co-activation ratios were established. Muscle activation levels increased by approximately 27% solely in the 1DS in both sidestepping phases. In the 2DS, the shift from a flexor dominant co-activation strategy in pre-contact toward extensor dominance in weight-acceptance commenced earlier for the high-level players. Quasi game-realistic information allowed for anticipatory increases in knee muscle activation regardless of expertise levels but only when the time demands to respond were low (1DS). High-level players were better at interpreting complex game-realistic information (2DS) to activate their knee extensors earlier in preparation for single-leg landing during weight-acceptance.     

游泳运动员手、足面积表型与运动等级的相关性研究

探讨手足相关派生指数与运动等级的相关度,为游泳运动员选材形态指标的精选提供理论依据。方法：对334名上海区级游泳学校、上海高校、上海市队、浙江省队游泳运动员手足表型进行测量统计并计算相应派生指数,对不同等级运动员手足面积表型与运动等级进行相关性分析。结果：男子游泳运动员手足面积表型与运动等级均无直线相关关系（相关系数小于0.3）,女子足部派生指标与运动等级亦均无直线相关关系,仅手部面积Ⅰ表型与运动等级存在极显著性低度直线相关（P＜0.01）。结论：手面积Ⅰ表型可入选女子游泳运动员二类选材指标。女子游泳运动员足面积表型和男子游泳员手足面积表型均不具备选材评价指标依据。