Effects of Sleep Deprivation on Driving Performance and Central Fatigue

The effects of sleep deprivation (SD) on performance, while contradictory at first glance, are in reality rather clear when exercise duration is considered, i.e. intense/supramaximal vs. prolonged exercises. This latter type of exercise leads to the most important performance decrements after SD. However, the causes of this accentuated fatigability in endurance exercise with sleep deficit are not known. Several hypotheses have been proposed such as lower pH before exercise, lower ventilation due to depreciated response to hypercapnia/hypoxia, or haemodilution. Yet the most plausible explanation is a lower tolerance to prolonged exercise because SD increases the rate of perceived exertion. Another potential effect of SD is an alteration of central command during exercise. The literature is rather scarce on this topic and is only based on a few animal studies. In humans, no effect of SD on maximal strength has been reported so that maximal voluntary activation should in theory not be altered. Transcranial Magnetic Stimulation (TMS), that allows to induce a motor response from its cortical origin (and to measure the resulting contraction), is a promising tool to explore neuromuscular function. TMS has been used only in three studies after SD, none of them involving exercise and none of them measuring mechanical responses (i.e. only EMG responses, such as motor evoked potential, were measured). In addition, the results of these three studies are contradictory. The effects of SD on central fatigue (i.e. increase of the activation deficit during exercise) have never been investigated. The goal of this experiment is thus to test the hypothesis that an increase in central fatigue (at supraspinal level) in SD can participate to performance alteration during a prolonged exercise. For that purpose, measurements of neuromuscular function particularly dedicated to assess central fatigue will be performed before and after SD but also when combining SD and a fatiguing exercise conducted until exhaustion.