Introduction: In competitive BMX racing, a fast start is crucial for success and requires good explosive strength through a wide movement velocity range. On the bike, and especially on the supercross starting ramp used in international competitions, technical demands increase compared to movements typically used for force-velocity (F-v) assessment, like jumping. This study investigated the transfer of F-v characteristics from jumping to two on-bike conditions varying in speed and technical difficulty, and their influence on starting speed. Methods Muscular power and F-v characteristics (Pmax: peak of P-v relationship; F0, v0, sF-v: intercepts and slope of F-v relationship) were obtained using squat jumps with various additional loads. Pedaling power and torque-cadence (T-Cad) characteristics (Pmax: peak of P-Cad relationship; T0, Cad0, sT-Cad: intercepts and slope of T-Cad relationship) were obtained with a modified, crank-based powermeter, under two conditions: • self-initiated sprint to maximum speed on flat ground • simulated supercross race start with randomized gate Various correlation analyses and t-tests were performed. Results: • Data were collected from 13 junior or senior national team pool riders. • Absolute Pmax jumping and sprinting were highly correlated, as were absolute F0 and T0. Among other F-v characteristics, and when normalized to body weight, no significant correlations were observed. • Absolute F0 was highly correlated with mean P and v over the first 30 m while sprinting. When F-v characteristics were normalized, the only significant correlation was between F0 and vmean. • Mean P and v on the starting ramp were highly correlated. Ppeak and Pmean for sprints and starts were highly correlated and values did not differ significantly between the two conditions. • For all T-Cad characteristics, significant correlations between sprinting and starting were revealed. However, all values differed significantly between the two conditions. • In absolute terms, all T-Cad characteristics correlated significantly with mean P and v on the starting ramp. When normalized, T0, Cad0 and Pmax correlated significantly with both mean P and v, however sT-Cad did not. Discussion In this study, nationally selected BMX racers could transfer muscular power quite well from simple jumping to complex sport-specific tasks. This confirms that good overall explosive strength is beneficial for pedaling power and most importantly, mean starting speed. However, neither F nor v confines of the F-v profile seemed to be limiting for sprint or start P and v, as the transfer of F-v characteristics was not uniform (involves additional skill). On the other hand, transfer of F-v characteristics from sprints to starts was rather uniform. Finally, since Pmax correlated most strongly of the T-Cad characteristics to mean starting v, whereas normalized sT-Cad did not, a preferable tendency toward particularly steep or flat T-Cad profiles is not apparent. Rather, absolute cycling peak P and Cad0 of around 250 rpm seem to be the most crucial determinants of starting speed. ABSTRACT FROM AUTHOR
© Copyright 2016 21st Annual Congress of the European College of Sport Science (ECSS), Vienna, 6. -9. July 2016. Veröffentlicht von University of Vienna. Alle Rechte vorbehalten.