Author(s): MURASE, M., SANO, Y., KAWABATA, M., SUMIYA, Y., WATANABE, Y., WATANABE, H., TAKAHIRA, N., Institution: KITASATO UNIVERSITY KITASATO INSTITUTE HOSPITAL, Country: JAPAN, Abstract-ID: 1423

INTRODUCTION:
Short-distance acceleration is performance-relevant in rugby, and rapid hip-extension/hamstring function is thought to contribute to early acceleration. Because rugby players differ substantially by position in body size and strength, it is important to determine whether field-test performance reflects acceleration-relevant neuromuscular function beyond these covariates. The maximum-speed single-leg bridge test (MS-SLBT) quantifies high-speed hip-extension performance (buttock-raising speed and height)1,2, but its independent associations with sprint section velocities after accounting for body size and knee flexor strength remain unclear. We examined these associations in high-school rugby players.
METHODS:
Seventy male high-school rugby players competing at the national top-8 level (Mean±SD: Age:16.1±0.8, Height:172.7±6.7cm, Body mass:80.2±12.4kg, Position: 39 forwards, 31 backs) were analyzed after exclusions. Participants completed a single maximal 40-m sprint on outdoor artificial turf. Timing gates at 0, 5, 10, 20, and 30 m were used to calculate mean velocities for 5–10 m, 10–20 m, and 20–30 m. MS-SLBT was performed with the dominant heel on a 40-cm platform for 20 consecutive repetitions “as fast and as high as possible”. Peak buttock-raising speed (m/s) and height (cm) were obtained from sagittal video (60 fps) using AI-based markerless motion analysis (SPLYZA Motion). Dominant-leg isometric knee flexion torque (Nm) was measured using a handheld dynamometer. Separate forced-entry multiple regression analyses were performed for each sprint interval, with mean interval velocity as the dependent variable and stature, body mass, dominant-leg knee flexion torque, and MS-SLBT buttock-raising speed and height as independent variables.
RESULTS:
All models were significant (5–10 m: R²=0.31; 10–20 m: R²=0.36; 20–30 m: R²=0.34; all p<0.001). In 5–10 m, interval velocity was independently associated with stature (B=0.013; β=0.269; p=0.040), body mass (B=−0.019; β=−0.739; p<0.001), MS-SLBT buttock-raising speed (B=0.717; β=0.378; p=0.036), and buttock-raising height (B=−0.038; β=−0.384; p=0.045), whereas knee flexion torque was not significant (p=0.194). In 10–20 m, stature (B=0.017; β=0.273; p=0.036), body mass (B=−0.024; β=−0.708; p<0.001), and buttock-raising speed (B=0.896; β=0.360; p=0.044) remained significant. In 20–30 m, only body mass remained significant (B=−0.029; β=−0.666; p<0.001).
CONCLUSION:
MS-SLBT buttock-raising speed was independently associated with early-interval sprint velocity (5–20 m) independent of stature and body mass. In contrast, isometric knee flexion torque was not a significant predictor of interval velocity. These findings suggest that rapid hip extension capacity—captured by MS-SLBT speed—contributes to early sprint acceleration and may serve as a practical, field-based indicator to identify and monitor acceleration-relevant function in high-school rugby.