Abstract des Autors

The countermovement jump (CMJ) is regularly tested in rugby league (RL), with recent work reporting reactive strength index modified (RSI mod) to distinguish between levels of play. Differences in CMJ-derived RSI mod and underpinning force-time variables between English Super League (SL) and RL Championship (RLC) players are, however, unknown. As SL and RLC teams compete against each other, this study addressed this knowledge gap. Sixty RL players from the English SL (n = 30) and RLC (n = 30) performed 3 CMJs on a force platform at the start of the preseason training. The RSI mod was calculated by dividing jump height (JH) by time to take-off (TTT), and several other variables were also extracted from the force-time record. The SL players achieved a significantly higher (large effect) RSI mod by performing the CMJ with a significantly shorter (large effect) TTT but a similar (small effect) JH. The SL players achieved the shorter TTT through a significantly reduced (large effects) relative displacement during both the countermovement (combined unweighting and braking displacement) and propulsion phases but a significantly higher (moderate effects) propulsion peak force and power. The relationships between TTT and relative countermovement (r = 0.719, p < 0.001) and propulsion (r = 0.771, p < 0.001) displacement for combined group data were very large. Practitioners working in RL should, therefore, consider reporting RSI mod and TTT, alongside JH, after CMJ force-time testing. We also suggest that RL players who produce lower RSI mod scores would benefit from being trained to produce larger CMJ propulsion forces over a shallower range of hip, knee, and ankle extension.