Objectives: To investigate the effects of fluid ingestion on neuromuscular function during prolonged cycling exercise. Methods: Eight well trained subjects exercised for 180 minutes in a moderate environment at a workload requiring ,60% maximal oxygen uptake. Two conditions, fluid (F) and no fluid (NF) ingestion, were investigated. Results: During maximal voluntary isometric contraction (MVC), prolonged cycling exercise reduced (p,0.05) the maximal force generating capacity of quadriceps muscles (after three hours of cycling) and root mean square (RMS) values (after two hours of cycling) with no difference between the two conditions despite greater body weight loss (p,0.05) in NF. The mean power frequency (MPF) for vastus lateralis muscle was reduced (p,0.05) and the rate of force development (RFD) was increased (p,0.05) only during NF. During cycling exercise, integrated electromyographic activity and perceived exertion were increased in both conditions (p,0.05) with no significant effect of fluid ingestion.
Conclusions:The results suggest that fluid ingestion did not prevent the previously reported decrease in maximal force with exercise duration, but seems to have a positive effect on some indicators of neuromuscular fatigue such as mean power frequency and rate of force development during maximal voluntary contraction. Further investigations are needed to assess the effect of change in hydration on neural mechanisms linked to the development of muscular fatigue during prolonged exercise. S everal factors are well known to play a role in the reduction of performance during prolonged muscle exercise. Within this framework, prevention of dehydration by adequate fluid replacement of body water losses during endurance exercise may maintain performance.1 For example, McConell et al 2 indicated that, when cyclists replaced their fluid losses fully during a two hour ride performed at 69% of peak oxygen consumption and 21˚C, they were able to cycle 53% longer in a subsequent exercise bout at 90% of peak oxygen consumption. On the one hand, the consequences of dehydration on the physiological factors of endurance performance, including rise in core temperature and cardiac output, are well documented.2-4 On the other hand, few experiments have analysed neuromuscular changes induced by dehydration. One study 5 indicated that sauna induced dehydration (,3% of body weight) resulted in an earlier increase in root mean square (RMS) and decrease in mean power frequency (MPF) during submaximal contraction. In contrast, Evetovich et al 6 did not find any difference in muscle fatigability between the two conditions, hydrated versus dehydrated. To the best of our knowledge, the effect of dehydration induced by dynamic endurance exercise on electromyographic (EMG) signals has been investigated only by Ftaiti et al. 7 They observed that the neuromuscular pattern of the knee extensor muscles assessed by mean EMG activity during a 40 minute submaximal running exercise in the heat was slightly altered despite a 2% loss of body weig...