Nt kinetics during the support phase of a maximum-velocity sprint. Methods: Four well-trained sprinters performed maximum-effort 60-m sprints. Two-dimensional high-speed video (200 Hz) and ground-reaction force (1000 Hz) data were collected at the 45-m mark. Horizontal velocity, step length, step frequency, and normalized moment, power, and work, via inverse dynamics, were calculated for two trials in each athlete. Results: The hip extensors performed positive work in early stance (normalized value = 0.063 ± 0.017), and the plantar flexors performed positive work in late stance (normalized value = 0.053 ± 0.010). The knee extensors played a negligible role in positive work generation throughout stance. Conclusions: In contrast to previous findings, the knee moment did not contribute substantially to power generation during the latter part of the support phase. This may be explained in part by the specific technical requirements of the maximum-velocity phase of the sprint. However, major periods of power generation of the hip extensors in early stance and of the plantar flexors in late stance were observed. The action of the knee joint during the support phase may therefore have been more of a facilitator for the radial transfer of power from the hip through the ankle on to the track....

S were recorded from publicly available television broadcasts, with 11 analyzed athletes performing in 10 or more races. For each run of each athlete, the average SF and SL over the whole 100-m distance was analyzed. To determine any SF or SL reliance for an individual athlete, the 90% confidence interval (CI) for the difference between the SF-time versus SL-time relationships was derived using a criterion nonparametric bootstrapping technique. Results: Athletes performed these races with various combinations of SF and SL reliance. Athlete A10 yielded the highest positive CI difference (SL reliance), with a value of 1.05 (CI = 0.50-1.53). The largest negative difference (SF reliance) occurred for athlete A11 as −0.60, with the CI range of −1.20 to 0.03. Conclusions: Previous studies have generally identified only one of these variables to be the main reason for faster running velocities. However, this study showed that there is a large variation of performance patterns among the elite athletes and, overall, SF or SL reliance is a highly individual occurrence. It is proposed that athletes should take this reliance into account in their training, with SF-reliant athletes needing to keep their neural system ready for fast leg turnover and SL-reliant athletes requiring more concentration on maintaining strength levels....

Sprint push-off technique is fundamental to sprint performance and joint stiffness has been identified as a performance-related variable during dynamic movements. However, joint stiffness for the push-off and its relationship with performance (times and velocities) has not been reported. The aim of this study was to quantify and explain lower limb net joint moments and mechanical powers, and ankle stiffness during the first stance phase of the push-off. One elite sprinter performed 10 maximal sprint starts. An automatic motion analysis system (CODA, 200 Hz) with synchronized force plates (Kistler, 1000 Hz) collected kinematic profiles at the hip, knee, and ankle and ground reaction forces, providing input for inverse dynamics analyses. The lower-limb joints predominately extended and revealed a proximal-to-distal sequential pattern of maximal extensor angular velocity and positive power production. Pearson correlations revealed relationships (P < 0.05) between ankle stiffness (5.93 ± 0.75 N · m · deg⁻¹) and selected performance variables. Relationships between negative power phase ankle stiffness and horizontal (r = −0.79) and vertical (r = 0.74) centre of mass velocities were opposite in direction to the positive power phase ankle stiffness (horizontal: r = 0.85; vertical: r = −0.54). Thus ankle stiffness may affect the goals of the sprint push-off in different ways, depending on the phase of stance considered.

The aim of this study was to investigate spatiotemporal and kinematic changes between the initial acceleration, transition and maximum velocity phases of a sprint. Sagittal plane kinematics from five experienced sprinters performing 50-m maximal sprints were collected using six HD-video cameras. Following manual digitising, spatiotemporal and kinematic variables at touchdown and toe-off were calculated. The start and end of the transition phase were identified using the step-to-step changes in centre of mass height and segment angles. Mean step-to-step changes of spatiotemporal and kinematic variables during each phase were calculated. Firstly, the study showed that if sufficient trials are available, step-to-step changes in shank and trunk angles might provide an appropriate measure to detect sprint phases in applied settings. However, given that changes in centre of mass height represent a more holistic measure, this was used to sub-divide the sprints into separate phases. Secondly, during the initial acceleration phase large step-to-step changes in touchdown kinematics were observed compared to the transition phase. At toe-off, step-to-step kinematic changes were consistent across the initial acceleration and transition phases before plateauing during the maximal velocity phase. These results provide coaches and practitioners with valuable insights into key differences between phases in maximal sprinting.

The initial steps of a sprint are important in team sports, such as rugby, where there is an inherent requirement to maximally accelerate over short distances. Current understanding of sprint acceleration technique is primarily based on data from track and field sprinters, although whether this information is transferable to athletes such as rugby players is unclear, due to differing ecological constraints. Sagittal plane video data were collected (240 Hz) and manually digitised to calculate the kinematics of professional rugby forwards (n = 15) and backs (n = 15), and sprinters (n = 18; 100 m personal best range = 9.96–11.33 s) during the first three steps of three maximal sprint accelerations. Using a between‐group research design, differences between groups were determined using magnitude‐based inferences, and within‐group relationships between technique variables and initial sprint acceleration performance were established using correlation. Substantial between‐group differences were observed in multiple variables. Only one variable, toe‐off distance, differed between groups (d = −0.42 to −2.62) and also demonstrated meaningful relationships with sprint performance within all three groups (r = −0.44 to −0.58), whereby a stance foot position more posterior relative to the centre of mass at toe‐off was associated with better sprint performance. While toe‐off distance appears to be an important technical feature for sprint acceleration performance in both sprinters and rugby players, caution should be applied to the direct transfer of other kinematic information from sprinters to inform the technical development of acceleration in team sports athletes.