Neuromuscular responses to hydration in moderate to warm ambient conditions during self-paced high-intensity exercise

Objective: To examine the neuromuscular responses to 60 minutes of self-paced high-intensity exercise punctuated with 6 x 1-minute all-out sprints at 10-minute intervals in moderate (19 8 degrees C, SEM 0 3) and warm (332, SEM 0 1), humid (similar to 64% relative humidity) conditions with either complete hydration (CH) or without hydration (NF) Design: Seven subjects (mean age 20 6 years (SE 11), mass 73.8 kg (SE 4 5), peak power 288 W (SE 11 3)) performed the time trial on four separate occasions, which were differentiated by ambient temperature and fluid ingestion For each sprint interval, distance, power output and electromyographic (EMG) data from the rectus femoris and vastus lateral's muscles were recorded Results: The NF trials resulted in a reduction in body mass for the moderate and warm conditions of 1 7% and 21%, respectively Final rectal temperatures were not different among conditions (similar to 38 7 degrees C) Total body sweating was higher in the warm condition 119 1-21 3 ml/kg per hour) compared with the moderate condition (16 1-16 5 ml/kg per hour, p<0 05) Neither fluid ingestion nor ambient temperature altered total distance cycled for any of the trials (range 30.1-32 6 km) The normalised integrated EMG (as percentage of maximal voluntary contraction) when compared with the first sprint increased from sprint three for the rectus femoris muscle in both no and complete hydration but decreased for the vastus lateral's muscle The mean percentile frequency shift increased for both the vastus lateral's and rectus lemons muscles in both no and complete hydration Conclusions: These results suggest that the integrity of the neuromuscular system is adjusted according to hydration status and ambient temperatures during intense self-paced cycling