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25.08.2010


Less sleep, less oxygen

Endurance athletes’ performance declines if they’ve had three hours too little sleep the night before. The shortage of sleep reduces their oxygen uptake and disrupts their heart beat, French sports scientists discovered in the early nineties.

In 1991 the researchers published the results of an experiment they did with 7 male cyclists aged 25. The cyclists had to bike a number of times, each time starting with a 10-minute warm up, then 20 minutes at 75 percent of their VO2max and finally cycling to exhaustion at rapidly rising intensity.

On one occasion the cyclists had slept normally the night before [spontaneous sleep, control night], on another occasion the researchers had deprived their subjects of three hours sleep [partial sleep deprivation, deprived night], and on yet another occasion the researchers gave the cyclists triazolam, a sleeping pill. The researcher hoped that this would improve the subjects’ quality of sleep, but that failed. We omit the results of the sleeping pill here.



The shortage of sleep reduced the athletes’ oxygen uptake; at least it did so when they were cycling at maximum intensity.



The athletes’ rate of respiration increased as a result of less sleep, but that didn’t help them with their oxygen uptake however.

As a result of the sleep shortage the athletes’ heart rate went up. The greater the intensity of effort, the greater the increase in heart rate.





The shortage of sleep also led to higher increases in lactic acid during maximal intensity exercise.



The researchers don’t really have an explanation for their observations, but they know from other studies that sleep deprivation raises the concentration in the body of stress hormones such as adrenalin and noradrenalin. The researchers believe that these hormones are responsible for an increase in heart rate and decrease in oxygen uptake.

Source:
Eur J Appl Physiol Occup Physiol. 1991; 63(2): 77-82.

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