Enduro mountain bike racing (enduro) consists of timed downhill race stages linked by non-competitive transition stages and general classification is determined by accumulated race stage time. Limited research is available on the physiological requirements of enduro despite a large population of professional elite riders. For this thesis, nine elite enduro athletes (n=8 male, n=1 female; top 100 world ranking) were recruited. Measures of daily training load (TL) and resting heart rate variability (HRV) were collected between three laboratory based tests throughout a season of training and racing. The demands of an international race event were assessed by heart rate, terrain induced accelerations and vibration exposure. Leukocyte subset (Neutrophils, CD4+ T-cell, CD8+ T-cell, and NK cell) redistribution, cortisol and IL-6 concentration were assessed at each laboratory test (pre, post, 1h-post) and the race event (pre, 1h-post, 19h-post). Main findings were that successful performance in enduro requires a large aerobic capacity (VO2peak = 61.1 ± 5.2 ml.kg.min?¹, power VO2peak = 410.9 ± 18.2W) coupled with adequate skill, technique and muscle mass to ensure high velocities can be sustained over differing types of terrain. Elevated TL appears to be a key component of training habit and the upper limit of training volume before negative adaptation was identified (>800 A.U. LuTRIMP). No relationship was found between TL and HRV. No significant changes were observed in leukocyte subset redistribution between laboratory tests. The race event induced significantly larger changes in circulating numbers of certain leukocyte subsets when compared to the laboratory test and the magnitude of redistribution of CD4- senescent T-cells was partially explained by vibration exposure (DeltaR² = -0.673, F(3,1) = 12.12, p = 0.04). A subsequent novel assessment of vibration loading in mountain biking revealed potentially damaging levels of vibration exposure that could be associated with long term health implications in enduro athletes (Ai(8) range 5.47 to 6.61ms-²). It was concluded that vibration exposure needs to be considered in future models of physiological loading in this discipline.
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