The dose-response relationship between training load and aerobic fitness in academy rugby union players

Purpose: The aim of this study was to identify the dose-response relationship between measures of training load (TL) and changes in aerobic fitness in academy rugby union players. Method: Training data from ten academy rugby union players was collected during a six-week in-season period. Participants completed a lactate threshold (LT) test which was used to assess VO2max and velocities at VO2max, 2 mmol·L-1 (vLT) and 4 mmol·L-1(vOBLA) as measures of aerobic fitness. Internal training load measures calculated were Banister’s TRIMP (bTRIMP), Edward’s TRIMP (eTRIMP), Lucia’s TRIMP (luTRIMP), individualised TRIMP (iTRIMP) and session-RPE (sRPE). External TL measures calculated were; total distance (TD), PlayerLoad™ (PL), high-speed distance >15 km·h-1(HSD), very high-speed distance >18 km·h-1 (VHSD) and individualized high-speed distance based on each player’s vOBLA (iHSD). Results: A second order regression (quadratic) analysis identified that bTRIMP (R2 = 0.78, P = 0.005) explained 78% of the variance and iTRIMP (R2 = 0.55, P = 0.063) explained 55% of the variance in changes in VO2max. All other HR based internal TL measures and sRPE explained less than 40% of variance with fitness changes. External TL explained less than 42% of variance with fitness changes. Conclusions: In rugby players bTRIMP and iTRIMP display a curvilinear dose-response relationship with changes in maximal aerobic fitness.