Mechanical work and physiological responses to simulated cross country mountain bike racing

The purpose was to assess the mechanical work and physiological responses to cross country mountain bike racing. Participants (n = 7) cycled on a cross country track at race speed whilst (V) over dotO(2), power, cadence, speed, and geographical position were recorded. Mean power during the designated start section (68.5 +/- 5.5 s) was 481 +/- 122 W, incurring an O-2 deficit of 1.58 +/- 0.67 L - min(-1) highlighting a significant initial anaerobic (32.4 +/- 10.2%) contribution. Complete lap data produced mean (243 +/- 12 W) and normalised (279 +/- 15 W) power outputs with 13.3 +/- 6.1 and 20.7 +/- 8.3% of time spent in high force-high velocity and high force-low velocity, respectively. This equated to, physiological measures for %(V) over dotO(2max) (77 +/- 5%) and % HRmax (93 +/- 2%). Terrain (uphill vs downhill) significantly (P < 0.05) influenced power output (70.9 +/- 7.5 vs 41.0 +/- 9.2% W-max), the distribution of low velocity force production, VO2 (80 +/- 1.7 vs 72 +/- 3.7%) and cadence (76 + 2 vs 55 +/- 4 rpm) but not heart rate (93.8 +/- 2.3 vs 91.3 +/- 0.6% HRmax) and led to a significant difference between anaerobic contribution and terrain (uphill, 6.4 +/- 3.0 vs downhill, 3.2 +/- 1.8%, respectively) but not aerobic energy contribution. Both power and cadence were highly variable through all sections resulting in one power surge every 32 s and a supra-maximal effort every 106 s. The results show that cross country mountain bike racing consists of predominantly low velocity pedalling with a large high force component and when combined with a high oscillating work rate, necessitates high aerobic energy provision, with intermittent anaerobic contribution. Additional physical stress during downhill sections affords less recovery emphasised by physiological variables remaining high throughout.