Use of Statistical Parametric Mapping to Reveal Novel Athlete-Specific Kinetic Determinants of Sprint Start Performance

The powerful development of force largely determines sprint start performance. However, to date, block phase kinetics have only been examined using discrete (0D) variables. One male sprinter completed 16 sprint starts whilst the ground reaction forces applied by each limb were measured. Kinetic predictors of horizontal external power were identified using Pearson r for 0D variables and statistical parametric mapping (SPM) to assess entire force curves. Pearson’s correlations revealed fast horizontal force production to result in better performance, but maximum forces appeared important only for the rear leg. Conversely, SPM results suggested that horizontal forces in the early push phase (initial 15-30%) were important for both legs. Testing entire force curves using SPM can supplement 0D analysis to identify kinetic factors which would otherwise be undetected

KINETIC FACTORS DIFFERENTIATING MID-TO-LATE SPRINT ACCELERATION PERFORMANCE IN SPRINTERS AND SOCCER PLAYERS

High-speed running in soccer is an important skill, however, the underlying kinetic factors are not fully understood. Ground reaction forces from steps 8 to 24 of maximal-effort sprints were captured for 24 soccer players and 28 track and field athletes using 54 force plates. Correlations between discrete force variables and horizontal acceleration were assessed, and statistical parametric mapping revealed performance associations across entire waveforms. Track and field athletes produced higher forces (mean anteroposterior: 1.56 N·kg-1) across shorter contacts (0.101 s) than soccer players (1.27 N·kg-1, 0.110 s). Interestingly, the technical ability to apply force and the performance-differentiating parts of stance were similar across groups. Thus, practitioners should perhaps target physical (force production) rather than technical factors to improve soccer players’ sprint abilities

USING COMPUTER VISION AND DEEP LEARNING METHODS TO CAPTURE SKELETON PUSH START PERFORMANCE CHARACTERISTICS

This study aimed to employ computer vision and deep learning methods in order to capture skeleton push start kinematics. Push start data were captured concurrently by a marker-based motion capture system and a custom markerless system. Very good levels of agreement were found between systems, particularly for spatial based variables (step length error 0.001 ± 0.012 m) while errors for temporal variables (ground contact time and flight time) were within 1.5 frames of the criterion measures. The computer vision based methods tested in this research provide a viable alternative to marker-based motion capture systems. Furthermore they can be deployed into challenging, real world environments to non-invasively capture data where traditional approaches would fail

THE INFLUENCE OF CHANGES IN SPRINT ABlLlN ON THE SLED VELOCIN PROFILE DURING THE SKELETON START

Sprint times are key predictors of skeleton start petformance, but the effect of enhancing sprint ability on the development of sled velocity is unknown. Twelve well-trained skeleton athletes performed three dry-land push-starts and three 30-m sprints before and after 16 training weeks. Sled velocity profiles were characterised using three descriptors (pre-load velocity, pre-load distance and load effectiveness) and a sled acceleration index was used to evaluate performance. Increases in pre-load velocity and distance were related to improved sprint times. However, enhanced sprint ability did not guarantee a faster start as reductions in load effectiveness were also observed when higher velocities were attained. Coaches could supplement physical conditioning with load technique training to potentially improve the transfer of training-induced sled velocity increases across the loading phase

Kinetic demands of sprinting shift across the acceleration phase: novel analysis of entire force waveforms

A novel approach of analyzing complete ground reaction force waveforms rather than discrete kinetic variables can provide new insight to sprint biomechanics. This study aimed to understand how these waveforms are associated with better performance across entire sprint accelerations. Twenty-eight male track and field athletes (100-m personal best times: 10.88 to 11.96 seconds) volunteered to participate. Ground reaction forces produced across 24 steps were captured during repeated (two to five) maximal-effort sprints utilizing a 54-force-plate system. Force data (antero-posterior, vertical, resultant, and ratio of forces) across each contact were registered to 100% of stance and averaged for each athlete. Statistical parametric mapping (linear regression) revealed specific phases of stance where force was associated with average horizontal external power produced during that contact. Initially, antero-posterior force production during mid-late propulsion (eg, 58%-92% of stance for the second ground contact) was positively associated with average horizontal external power. As athletes progressed through acceleration, this positive association with performance shifted toward the earlier phases of contact (eg, 55%-80% of stance for the eighth and 19%-64% for the 19th ground contact). Consequently, as athletes approached maximum velocity, better athletes were more capable of attenuating the braking forces, especially in the latter parts of the eccentric phase. These unique findings demonstrate a shift in the performance determinants of acceleration from higher concentric propulsion to lower eccentric braking forces as velocity increases. This highlights the broad kinetic requirements of sprinting and the conceivable need for athletes to target improvements in different phases separately with demand-specific exercises.</p

The effect of altering loading distance on skeleton start performance: Is higher pre-load velocity always beneficial?

Athletes initiating skeleton runs differ in the number of steps taken before loading the sled. We aimed to understand how experimentally modifying loading distance influenced sled velocity and overall start performance. Ten athletes (five elite, five talent; 67% of all national athletes) underwent two to four sessions, consisting of two dry-land push starts in each of three conditions (preferred, long and short loading distances). A magnet encoder on the sled wheel provided velocity profiles and the overall performance measure (sled acceleration index). Longer pre load distances (12% average increase from preferred to long distances) were related to higher pre-load velocity (r = 0.94), but lower load effectiveness (r = 0.75; average reduction 29%). Performance evaluations across conditions revealed that elite athletes’ preferred distance push starts were typically superior to the other conditions. Short loading distances were generally detrimental, whereas pushing the sled further improved some talent-squad athletes’ performance. Thus, an important trade-off between generating high pre load velocity and loading effectively was revealed, which coaches should consider when encouraging athletes to load later. This novel intervention study conducted within a real-world training setting has demonstrated the scope to enhance push-start performance by altering loading distance, particularly in developing athletes with less extensive training experience

Skeleton sled velocity profiles:a novel approach to understand critical aspects of the elite athletes’ start phases

The development of velocity across the skeleton start is critical to performance, yet poorly understood. We aimed to understand which components of the sled velocity profile determine performance and how physical abilities influence these components. Thirteen well-trained skeleton athletes (&gt;85% of athletes in the country) performed dry-land push-starts alongside countermovement jump and sprint tests at multiple time-points. A magnet encoder attached to the sled wheel provided velocity profiles, which were characterised using novel performance descriptors. Stepwise regression revealed four variables (pre-load velocity, pre-load distance, load effectiveness, velocity drop) to explain 99% variance in performance (β weights: 1.70, –0.81, 0.25, –0.07, respectively). Sprint times and jump ability were associated (r ± 90% CI) with pre-load velocity (–0.70 ± 0.27 and 0.88 ± 0.14, respectively) and distance (–0.48 ± 0.39 and 0.67 ± 0.29, respectively), however, unclear relationships between both physical measures and load effectiveness (0.33 ± 0.44 and –0.35 ± 0.48, respectively) were observed. Athletes should develop accelerative ability to attain higher velocity earlier on the track. Additionally, the loading phase should not be overlooked and may be more influenced by technique than physical factors. Future studies should utilise this novel approach when evaluating skeleton starts or interventions to enhance performance

Training-related changes in force-power profiles:Implications for the skeleton start

Purpose: Athletes' force-power characteristics influence sled velocity during the skeleton start, which is a crucial determinant of performance. This study characterized force-power profile changes across an 18-month period and investigated the associations between these changes and start performance. Methods: Seven elite- and 5 talent-squad skeleton athletes' (representing 80% of registered athletes in the country) force-power profiles and dry-land push-track performances were assessed at multiple time points over two 6-month training periods and one 5-month competition season. Force-power profiles were evaluated using an incremental leg-press test (Keiser A420), and 15-m sled velocity was recorded using photocells. Results: Across the initial maximum strength development phases, increases in maximum force (Fmax) and decreases in maximum velocity (Vmax) were typically observed. These changes were greater for talent (23.6% and-12.5%, respectively) compared with elite (6.1% and-7.6%, respectively) athletes. Conversely, decreases in Fmax (elite-6.7% and talent-10.3%) and increases in Vmax (elite 8.1% and talent 7.7%) were observed across the winter period, regardless of whether athletes were competing (elite) or accumulating sliding experience (talent).When the training emphasis shifted toward higher-velocity, sprint-based exercises in the second training season, force-power profiles seemed to becomemore velocity oriented (higher Vmax andmore negative force-velocity gradient), which was associated with greater improvements in sled velocity (r = .42 and-.45, respectively). Conclusions: These unique findings demonstrate the scope to influence force-power-generating capabilities in well-trained skeleton athletes across different training phases. To enhance start performance, it seems important to place particular emphasis on increasing maximum muscle-contraction velocity.</p

The effect of altering loading distance on skeleton start performance: Is higher pre-load velocity always beneficial?

Athletes initiating skeleton runs differ in the number of steps taken before loading the sled. We aimed to understand how experimentally modifying loading distance influenced sled velocity and overall start performance. Ten athletes (five elite, five talent; 67% of all national athletes) underwent two to four sessions, consisting of two dry-land push starts in each of three conditions (preferred, long and short loading distances). A magnet encoder on the sled wheel provided velocity profiles and the overall performance measure (sled acceleration index). Longer pre load distances (12% average increase from preferred to long distances) were related to higher pre-load velocity (r = 0.94), but lower load effectiveness (r = 0.75; average reduction 29%). Performance evaluations across conditions revealed that elite athletes’ preferred distance push starts were typically superior to the other conditions. Short loading distances were generally detrimental, whereas pushing the sled further improved some talent-squad athletes’ performance. Thus, an important trade-off between generating high pre load velocity and loading effectively was revealed, which coaches should consider when encouraging athletes to load later. This novel intervention study conducted within a real-world training setting has demonstrated the scope to enhance push-start performance by altering loading distance, particularly in developing athletes with less extensive training experience

Kinetic determinants of athletics sprint start performance

The sprint start lays a foundation to a good performance of track athletes. Thus, the aim was to understand the key force production determinants of the athletics sprint start. Eleven male athletes performed normal sprint starts with ground reaction forces collected at 1000 Hz from under each extremity separately. Key kinetic variables were analysed from six starts from each athlete and correlated with the horizontal external power. Several force and timing variables provided statistically significant correlations, but especially the high ratio of forces at 58.9 ± 3.5% with r = .941 (p = .000) demonstrated the importance of horizontal force production during the start. Better performers reached large forces on the blocks quicker, although it was interesting that the actual rate of force production did not statistically significantly correlate with the horizontal external power