Objective: This study examined the neuromuscular responses to 60 min of self-paced high intensity exercise punctuated with 6 x 1 min “all-out” sprints at 10 min intervals in moderate (19.8 ± 0.3° C) and warm (33.2 ± 0.1°C), humid (~ 64% relative humidity) conditions with either complete hydration (CF) or without hydration (NF).
Design: Seven subjects (mean ± SE; age 20.6 ± 1.1 yr, mass 73.8 ± 4.5 kg, peak power 288 ± 11.3 W) 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 lateralis muscles were recorded.
Results: The NF trials resulted in a reduction in body mass for the moderate and warm conditions of 1.7% and 2.1%, respectively. Final rectal temperatures were not different among conditions (~ 38.7 °C). Total body sweating was higher in the warm condition (19.1 – 21.3 mL/kg/h) compared with the moderate condition (16.1 – 16.5 mL/kg/h; 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 iEMG (as % maximal voluntary contraction) when compared with the first sprint increased from sprint three for the rectus femoris muscle in both NF and CF but decreased for vastus lateralis muscle. However, the mean percentile frequency shift increased for both vastus lateralis and rectus femoris muscles in both NF and CF.