Endurance training: sleep to win!

The importance of enough good-quality sleep for mental performance has long been understood. In the last two decades or so however, researchers have concluded that sleep also has a huge role in regulating many physiological functions, which can directly affect performance⁽¹⁾. In short, even though there is still a widespread perception among the public (and many athletes too) that sleep quality and quantity don’t really matter that much, the fact is that they certainly do!

Understanding sleep deficiency effects

Research has identified that when you go short of restful, high-quality sleep, there are a number of potential performance consequences. Both total and partial sleep deprivation over a period of days have been shown to impair exercise performance; research has shown that a single night of sleep deprivation can decrease performance during an endurance running test on the following day^(2-6). These same studies also suggest that maximal aerobic power may decline by up to 50% after partial sleep deprivation and that losing four hours of your normal sleep can significantly reduced both peak and mean power outputs during 30-seconds maximal sprints. All of the above are compounded by the fact that sleep deprivation, especially when chronic, can lead to a lack of motivation to train and reduced ability to think clearly!

Much of the research studies into sleep (deprivation) and performance have been laboratory based, where athletes started the trial fresh, underwent a period of sleep deprivation and then were assessed during a subsequent exercise test. However, most athletes train on a day to day basis, and fairly recent research also points to the fact that a bad night’s sleep during a run of training days affect can negatively impact an athlete’s ability to perform in those later training days.

Sleep loss during normal training

In a 2021 study, which SPB previously reported on, Korean scientists looked at the impact of sleep deprivation on the next day’s exercise performance after a day when vigorous training had taken place (ie more reflective of normal training routines)⁽⁷⁾. Eleven athletes completed two identical exercise trials on two separate occasions:

·        Day 1 – Ninety minutes of continuous running at 75% VO2max (moderate-hard intensity) followed by 100 drop jumps to induce high levels of muscle fatigue.

·        Day 2 – Twenty minutes of sub-maximal running at 75% VO2max and then a time to exhaustion running test (TTE) at 85% of VO2max (hard to very hard).

The only difference between the two trials was that in one trial (the control), the athletes were allowed to sleep for eight hours on the night of day #1, while in the other trial however, sleep duration was shortened to just 40% of normal (ie just under three and a quarter hours) between days 1 and 2. When comparing the normal sleep/sleep deprived performance results on day #2, the research discovered that there was a big impact on performance; the time to exhaustion at 85% VO2max was very significantly shorter in the sleep deprivation trial than in the full night’s sleep trial (665 seconds vs. 887 seconds – see figure 1). Also, when sleep deprived, the athletes were less able to draw on their muscle carbohydrate (glycogen) reserves - either because the sleep deprivation made it more difficult to do so, or because it had somehow negatively impacted their ability to synthesize muscle glycogen overnight following the food intake the evening before.

Figure 1: Time to exhaustion at 85% VO2max in full vs. deprived sleep