Hypohydration, heat and 4000m cycling performance

Relatively little is known about the effects of hypohydration and heat during 'middle distance' sporting events that place great demands on both the aerobic and anaerobic energy systems. Seven moderately trained male cyclists performed three 4000m maximal cycling trials in differing conditions and in a random order, to determine whether hydration status and heat were associated with variations in performance. Trials were paced to half distance. The conditions were i) euhydrated exercise (EUH), ii) hypohydrated exercise (HYP), involving exercise induced dehydration to 2% of total body mass, and iii) hypohydrated exercise coupled with an ambient temperature of 30°C (HYP+H). Mean resting heart rates were significantly elevated in the HYP+H condition compared with the EUH condition (p<0.01). Trial performance times were significantly shorter in the EUH and HYP conditions compared with the HYP+H condition (p<0.01), although split times were similar. This was due to the mean power output (MPO) being significantly lower during the last 1000m of the HYP+H condition (p<0.01). It appears that moderate hypohydration alone did not affect 4000m cycling time trial performance. However, when coupled with an ambient temperature of 30°C a performance decrement was observed. As anaerobic and aerobic responses were similar between trials it appears that some other factor(s) (peripheral fatigue or a reduced central drive), possibly related to elevated muscle or core temperatures, may have led to the decrement in performance.