ECSS Paris 2023: CP-BM10
INTRODUCTION: Repeated sprint exercise (RSE), involving maximal-intensity efforts with short recovery intervals until exhaustion, is a widely used and effective training method among athletes. However, the characteristics of neuromuscular behavior involvement during RSE remain unclear. Purpose of this study was to investigate neuromuscular fatigue during RSE from the perspective of neuromuscular responses in track and field sprinters. METHODS: The task was repeated 30-m maximal sprint running. Nine male track and field athletes participated in this study. Each continued until their sprint time declined by 10% compared with the first trial, with 20 s of rest between runs. Surface electromyography (EMG) was recorded from eight muscles of one lower limb (gluteus maximus, rectus femoris, biceps femoris, semitendinosus, vastus lateralis, tibialis anterior, soleus, gastrocnemius lateralis). Spatiotemporal variables were measured using a high-speed camera and timing gates. The running cycle was divided into four phases (contact, early-swing, mid-swing, and late-swing), and integrated EMG (iEMG) was calculated for each four phases. Three sprints were analyzed: the first trial, the trial at 5% speed reduction, and the trial at 10% reduction. RESULTS: As fatigue progressed, running speed and step frequency significantly decreased. Significant interactions were observed for iEMG in the rectus femoris and gluteus maximus. In particular, rectus femoris activity decreased during early and mid-swing, while gluteus maximus activity decreased during stance, mid-swing, and late-swing phases. CONCLUSION: An important finding of this study was that neuromuscular activity of the hip muscles was selectively attenuated as fatigue progressed during repeated sprint exercise. These muscles play a key role in sprint acceleration by generating ground reaction force through hip extension and facilitating swing-leg recovery, and are therefore essential for achieving high running speed. The present results indicate that neuromuscular fatigue during repeated sprint exercise does not occur uniformly across all muscles, but rather selectively, reflecting muscle-specific characteristics. Despite the decline in sprint performance, several muscles maintained relatively stable activation, suggesting compensatory motor control strategies to preserve overall movement patterns under fatigued conditions. This selective fatigue behavior may be related to differences in functional roles, mechanical loading, and fatigue resistance among muscles. From a practical perspective, these findings highlight the importance of training interventions aimed at improving fatigue resistance of the hip extensors and flexors to maintain sprint performance during repeated high-intensity efforts. In conclusion, neuromuscular fatigue during repeated sprint exercise is characterized by muscle- and phase-specific alterations in activation, highlighting the importance of hip musculature in repeated sprint performance.
Read CV GAKU KAKEHATAECSS Paris 2023: CP-BM10
INTRODUCTION: In the 4×100 m relay, outcome depends not only on sprint capacity but also on baton-exchange efficacy. Yet quantitative evidence on how exchange kinematics affect performance in elite teams remains limited. We aimed to identify the main determinants of exchange efficacy, and to quantify exchange-related time loss by comparing observed data with best-possible performance estimated via simulation. METHODS: Eight teams per men’s and women’s final were recorded by seven high-speed cameras (239.76 fps). Multi-view 3-D reconstruction yielded runners’ velocity profiles, and exchange onset and completion were identified from video. We measured takeover-zone time, bottom velocity of baton (minimum of incoming and outgoing runner velocities), exchange position, free distance (distance between runners at exchange completion), and exchange duration. Best-possible baton velocity was then simulated by modeling minimal incoming deceleration (linear) and near-maximal outgoing acceleration (exponential) and by placing the exchange at the velocity crossover point. Achievement ratios for takeover-zone time and bottom velocity of baton were computed by comparing observed with simulated values. RESULTS: Simulated finish times were 0.22 to 0.54 s faster than observed in men and 0.12 to 0.80 s faster in women. Exchange-related time loss varied widely from one team to another and was not necessarily smaller in higher-ranked teams. Takeover-zone time achievement ratio ranged from 90.5 to 99.4% in men and 89.9 to 100.0% in women, differing by up to 10 percentage points. Bottom velocity of baton correlated strongly with takeover-zone time in both sexes and in both observed and simulated datasets (r = −0.711 to −0.962). Their achievement ratios were also correlated (r = 0.828 to 0.935). Observed exchange position was consistently earlier than simulated optimal and was associated with both achievement ratios (r = 0.532 to 0.754). Free distance also correlated with both achievement ratios (r = 0.444 to 0.666), whereas exchange duration showed no association with either. CONCLUSION: Exchange-related time loss is substantial and varies widely across teams, confirming room for improvement even for the highest-ranked teams. Efficacious exchanges are governed primarily by preserving baton velocity. When the incoming runner covers most of the takeover zone at high velocity and the outgoing runner accelerates maximally, a short takeover-zone time is achieved with a later exchange position. Conversely, when the incoming runner approaches too early, spacing collapses and free distance shortens; the incoming runner decelerates, the outgoing runner has not fully accelerated, and baton velocity drops—lengthening takeover-zone time. Exchange position and free distance likely reflect these velocity conditions rather than acting as independent causal factors. Teams should prioritize protecting baton velocity by minimizing velocity loss, then fine-tune exchange position while balancing gains against disqualification risk.
Read CV Takeo MatsubayashiECSS Paris 2023: CP-BM10
INTRODUCTION: Temporal gait outcomes such as contact time (CT), flight time (FT) and temporal asymmetry often directly informs training loads and Return to Play decisions. However, difficulties arise quantifying precise gait event timing outside laboratory contexts without motion capture. Wearable inertial measurement units (IMUs) offer an applied pathway; however, translation to training and competition requires validated, high resolution gait event detection pipelines in controlled settings before broader ecological deployment. METHODS: Running-trained athletes (n=14; 7 female) completed repeated constant-speed treadmill running trials (25 s, 10–20 km·h⁻¹). Bilateral ankle IMUs (1080 Hz; 20 mm proximal to the lateral malleoli) were synchronised with high-speed video (240 fps) to generate sample-level contact and flight labels for training and testing. A novel high-resolution 1D convolutional neural network (CNN) classified gait phase from short non-overlapping windows (~2.78 ms) to prioritise precise transition timing, with pre-processing to standardise left-right coordinate conventions and deterministic post-processing to enforce physiological plausibility. Model performance was evaluated using precision, recall, F1 and Youden’s J; metrics were computed per participant × speed to avoid pseudo replication. Agreement of derived CT/FT/asymmetry against video was quantified using Lin’s CCC and Bland–Altman (bias and 95% limits of agreement). Test-retest reliability used ICC(2,1) on athlete means across repeated speed pairs; model repeatability used ICC(2,1) across two independent training runs. RESULTS: Across 14 athletes and >9.4 million tested samples, the CNN pipeline demonstrated high discrimination (precision 0.956; recall 0.973; F1 0.965), with consistently strong sensitivity/specificity across speeds (Youden’s J 0.944-0.956). Agreement with video showed small CT/FT bias (0.001 s / -0.002 s) and narrow 95% limits of agreement (CT -0.012-0.015 s; FT -0.020-0.016 s), with proportional bias detected (p<0.001). Reliability of CT/FT improved with speed (CT ICC up to 0.91; FT ICC up to 0.97), while asymmetry reliability was poorest at slower speeds and acceptable at moderate-fast speeds. Model repeatability across independent training runs was near-perfect (CT/FT ICC > 0.99; asymmetry ICC 0.76-0.99), indicating that observed between-trial variability was driven primarily by biological and experimental factors rather than model instability. CONCLUSION: A bilateral ankle-IMU + CNN pipeline enables accurate CT and FT estimation across treadmill speeds, supporting scalable athletic performance monitoring. Asymmetry outcomes require cautious interpretation due to error propagation when true asymmetries are small yet demonstrate more robustness when aggregated across sufficient steps. Future work will extend validation to field-based running and optimise pipeline components to enhance ecological robustness and accelerate widescale adoption in applied settings.
Read CV Lauren WoodECSS Paris 2023: CP-BM10