The effects of moderate sleep loss on sleepiness levels and neuromuscular function in healthy males
Sleep loss studies have traditionally focused on cognitive tasks involving alertness, memory, learning and reaction time as well as mood changes and increases in daytime sleepiness. The effects of sleep loss on neuromuscular performance are less well described and understood. Moderate sleep, i.e. loss of a few hours sleep a night, has not been studied with regard to muscular performance. This study examined the effect of moderate sleep loss on sleepiness levels and neuromuscular performance. Nine male subjects (30-50 yr) participated in a cross-over design study and were assessed for sleepiness levels by subjective sleep scales, central nervous system (CNS) arousal by critical flicker fusion (CFF), muscle strength and estimates of submaximal force production for both handgrip and the quadriceps muscle group, and finally fatigue was assessed by repeated maximum voluntary contractions (MVCs) for the quadriceps muscle group. The study was conducted over a five week period and each subject reduced their sleep by 2 hr i.e. from 8 hr to 6 hr for one week. The subjects also completed a daily sleep log that reflected their sleep behavior over the study period. The neuromuscular performance assessments were conducted at the same time of day for each subject to minimise circadian rhythm affects. The results showed with moderate sleep loss, a significant increase in daytime levels of sleepiness as assessed by the Stanford Sleepiness and Epworth Sleepiness scales. There was an increase in negative mood states and a decrease in daily exercise times during the week of moderate sleep loss for those subjects who had normal daily exercise times that exceeded an hour. CFF did not change with moderate sleep loss. There was a 9% decrease in quadriceps maximal force and this was greater than the 2% decrease for handgrip maximal force. The decreases in muscle strength showed greater response from some individuals. Subjects were able to estimate submaximal force production and this estimation did not change with moderate sleep loss. There was no change in the rate of force decline (i.e. fatigue) for repeated MVCs. The conclusions from the study suggest that moderate sleep loss does increase levels of daytime sleepiness and the effect on neuromuscular performance is limited to some effects on maximal force production.