Sleep & Performance
There was a 2015 review article published in Sports Medicine, titled "Sleep and Athletic Performance: The Effects of Sleep Loss on Exercise Performance, and Physiological and Cognitive Responses to Exercise.”
Below I provide a summary of the authors’ main points, followed by my 2 cents (interpretation of the results) from a coach’s perspective.
Authors’ Main Points:
Although sleep is considered critical to optimal performance, many athletes appear to lose sleep prior to competition for various reasons, including noise, light, and a dose of anxiety. While there appears to be sufficient evidence that complete sleep deprivation can have significant negative effects on athletic performance, the negative effects of sleep restriction (partial disturbance of the sleep–wake cycle) are not as consistent; a relevant point, given that athletes are more likely to experience this latter mode of sleep loss.
The detrimental effect of sleep loss on most aspects of cognitive function remains undeniable, findings that would predictably suggest negative consequences for athletes requiring a high degree of neurocognitive reliance; however, if the degree of sleep restriction is only mild, then there might not be a hindrance on cognitive performance. In other words, much of the previous research has reported that cognitive performance is negatively affected following sleep loss; however, conflicting findings mean that the extent, influence, and mechanisms of sleep loss affecting such performance remain uncertain.
For instance, research indicates that performance can be maintained for relatively simple tasks, like maximal physical efforts and/or gross motor performances. In comparison, studies investigating the effect of sleep loss in athletes have shown detriments in sport-specific performances that require a higher degree of skill/coordination. So, it depends on the task at hand…how simple vs. complicated are the demands in terms of cognition and/or coordination?
The effects of sleep loss on physiological responses to exercise also remain equivocal (there is evidence on both sides); however, it appears a reduction in sleep quality and quantity could result in an autonomic nervous system imbalance, simulating symptoms of overtraining. Additionally, increases in pro-inflammatory cytokines following sleep loss could promote immune system dysfunction.
My Two Cents:
For those who read the fine print of this review article and saw that the several studies showing a decrease in performance were mostly testing maximal power output (i.e., 30-sec Wingate/cycling sprint test), I would ask them to raise their hand if that is a meaningful carryover into their own training (answer: most likely not).
The key distinction lies in whether we’re talking sleep deprivation vs. sleep restriction, and this is where the other significant findings of the article are contained, with most of us amateur athletes (myself included) rarely facing actual sleep deprivation. In short, if it’s the night before a race and you don’t get much sleep, then don’t worry about it, especially since there are very little (if at all) cognitive aspects of endurance events, whereas team-sport athletes might have other considerations depending on their position/demands, but even then the results are mixed with no need to sound an alarm. Honestly, who sleeps like a rock the night before they play in the Super Bowl or compete for Olympic gold!?
It’s important to note that the article points out that sleep restriction doesn’t always reveal adverse effects on physiological measures, so the authors postulate that central fatigue (i.e., central nervous system fatigue/ “self-talk”) is most likely the mechanism, especially if you factor that perceived exertion (effort) was diminished in some studies. In other words, if the athlete believes that the sleep restriction is going to have an adverse effect, then he/she might be likely to create a self-fulfilling prophecy! Get the idea out of your head, and do so with confidence, as the empirical evidence supports that short-term sleep restriction likely won’t affect your endurance the following day.
Chronic sleep restriction is a separate issue not addressed by this article, and I think we would all agree that there would certainly be performance detriments in this case (even if just a few days), along with an increased chance for injury (i.e., relationship between chronic muscular fatigue and injury). I can empathize with any athlete who doesn't get a solid night of sleep the night before a big game/race, but what’s probably more important is the sleep you get two and three nights before a your key event.
Train Smarter, Not Harder!
Mike