Effects Of Cycling In The Cold On Neuromuscular Activation And Fatigue

Abstract

PURPOSE: To examine the effects of cold exposure on neuromuscular activation and fatigue during aerobic cycling exercise. METHODS: Five apparently healthy males (24.8 + 2.9 years; 183.1 + 2.2cm; 80.5 + 4.4kg; 11.3 + 2.8%BF; 3.97 + 0.34 L[BULLET OPERATOR]min-1) visited the laboratory on three separate occasions. During the first visit, participants performed a VO2max test on a Velotron cycle ergometer. During the two remaining trials, participants performed two, five-second maximal isometric voluntary contractions (MVICs) of the right leg extensors prior to entering the environmental chamber. In the environmental chamber, volunteers cycled for 60 min at 60% of their VO2max in either a low- (5°C / 45%RH; LT), or moderate-temperature (22°C / 45%; MT), in counterbalanced fashion. Electromyography (EMG) of the vastus lateralis was recorded during the 60-minute exercise protocol during the first two minutes, and during the last two minutes of every 10-minute period (0-2min, 8-10min, 18-20min, 28-30min, 38-40min, 48- 50min, 58-60min). Root mean square (RMS), mean power frequency (MPF) and median power frequency (MEDPF) were then normalized to the MVIC for each time point. Data were analyzed using a within subjects repeated measures ANOVA. RESULTS: No significant differences were observed between conditions (LT and MT) for RMS (F = ; p = 0.591) MPF (F = 0.003; p = 0.959), or MEDPF (F = 1.438; p=0.297). A significant main effect of time was observed for RMS F = 8.187, p<0.001). Specifically, RMS at 8-10Min (26.369 + 3.542%), 18-20Min (24.782 + 3.572%), 38-40Min (25.722 + 3.534%) and 48-50Min (26.070 + 3.451%) were significantly lower than RMS at 58-60Min (27.091 + 3.521%). There was also a significant effect of time for MPF (F = 3.049; p = .023), with a significantly higher MPF at 18-20min (85.694 + 1.467%) and 38-40min (85.942 + 1.408%) compared to 8-10min (83.165 + 1.215%). CONCLUSION: The increase in RMS observed at the end of exercise suggests an increase in neural drive and motor unit activity, suggestive of an increase in motor unit recruitment and fatigue during aerobic cycling exercise at 60% VO2max. Furthermore, MPF significantly increased from the beginning of exercise, suggesting an increase in action potential conduction velocity.