Science of Sport: Sleep deprivation

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Participants in adventure racing often go without sleep for more than 24 hours while engaging in prolonged sub-maximal exercise. Does the sleep deprivation harm their capacity to perform this exercise? Not at all, according to a new UK study.

Researchers from Bath and Hull Universities set out to examine the effects of 30 hours of sleep deprivation and intermittent physical exercise on cardio-respiratory markers of sub-maximal exercise.

Six male students endured 30 hours of sleep deprivation in a laboratory under two different conditions, separated by seven days, as follows:

• Performing sedentary activities;
• Undertaking intermittent cycling for 20 minutes every two hours at 50% of VO₂max.

Every four hours, the subjects in both groups completed assessments of cardiorespiratory function while cycling at 50% VO₂max.

Analysis of the results showed no significant differences between baseline assessment and the two sleep deprivation conditions for any of the measured respiratory variables. Additionally, there were no significant differences for any variable between the two experimental groups. And, while mean heart rate in the sedentary condition was lower than at baseline, the same was not true of the exercise condition.

‘The main finding of this study,’ point out the researchers, ‘was that, with the exception of heart rate that was significantly lower in the sedentary sleep deprivation condition, neither sleep deprivation nor sleep deprivation combined with physical exercise were associated with significant effects on measured markers of submaximal exercise performance.’

This finding, they add, appears consistent with the theory that the effects of sleep loss occur at higher brain centres involved with ‘integrative function’.

What does this mean in practice for sportsmen and women? The researchers conclude: ‘The apparent resilience of cardiorespiratory responses in subjects deprived not only of sleep but of both sleep and rest would suggest that, from a physiological perspective, sleep loss should not be considered a limiting factor in the performance of sustained moderate physical exertion, as often demanded by continuous multi-day endurance events.

‘However, since sleep deprived subjects [in other studies] have displayed reduced tolerances to prolonged exercise, it would appear that the mechanisms of reduced tolerance may lie elsewhere. The increased negative disturbances to subjective ratings of mood with sleep deprivation seen in previous studies may be one such mechanism that leads to an augmentation in the perception of exercise intensity, and a decreased willingness to exert maximal effort.’

Int J Sports Med 2004;25:421-426

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