Physiology Friday #137: How Sleep Loss Affects Your Physical Performance
Less shuteye means fewer personal records.
Hello friend.
Welcome to Physiology Friday.
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Poor sleep, poor performance
Social media health influencers and well-credentialed experts constantly badger us about sleep. By now, most of us have heard about the harms of insufficient sleep, poor quality sleep, or the lethal combination of the two — effects that range from an elevated risk for cardiovascular disease and cognitive decline, to metabolic dysfunction and insulin resistance.
Though well-worn, the advice to “sleep more” and “sleep better” is still important to reiterate from time to time. After all, sleep governs every aspect of our physical and mental performance.
However, this impact on performance is often hard to quantify. Sure, the day after a night of poor sleep, it’s easy to notice that we’re thinking slower, typing a bit more sluggishly at our computer, and forgetting a lot more (just me?). We might even have less motivation to hit the gym or, if we are motivated enough to make the commute, we may feel like our effort level is well above normal or our ability to lift a normally-easy weight is impaired.
A number of studies have investigated how sleep loss impacts physical performance, strength, endurance, and any number of other performance metrics. A recent meta-analysis synthesized findings from this broad swath of literature, and the results paint a pretty comprehensive (and objective) picture of the impact that sleep loss has on performance. Spoiler alert, it isn’t pretty.
A total of 77 studies were included in the review. The sleep loss interventions included sleep deprivation (participants received no sleep in the previous 24 hours) and sleep restriction (participants slept less than 6 hours in the previous 24 hours).
The sleep restriction interventions were further divided up into early and late sleep restriction. Early restriction means that an individual’s bedtime was shifted later, but wake time was kept the same. Late restriction means that an individual’s wake time was shifted earlier, while bedtime remained the same. Though this seems like an arbitrary distinction, these two types of sleep restriction can have different effects on physiology and might be expected to impact performance in unique ways.
Several different performance outcomes were analyzed:
Overall exercise performance (all modalities combined)
Anaerobic power (i.e., activities lasting less than 6 seconds performed with maximal effort)
Speed/power endurance (i.e., maximal-effort exercise lasting up to 90 seconds)
High-intensity interval exercise (HIIT; repeated ~45-second near-max efforts with recovery periods in between)
Strength (i.e., single-effort maximal force development or 1-repetition max)
Endurance (i.e., continuous aerobic exercise lasting more than 2 minutes)
Strength-endurance (i.e., resistance exercise with multiple repetitions or involving sustained contractions
Skill (i.e., coordination, physical tasks requiring a cognitive component, sport-specific skills)
And finally, the analysis also considered the time of day when exercise was performed — separating this factor into AM and PM exercise.
Let’s take a look at some of the findings. For the sake of brevity, I’ll discuss all outcomes combined in the context of sleep loss, before providing a table of outcome-specific results and some key highlights.
Overall exercise performance
Overall, any form of sleep loss reduced performance by 7.6%, and the performance decline was greater when exercise was performed in the PM (8.3%) compared to the AM (5.4%). Sleep deprivation specifically reduced performance by 5.3%, effects that were greater in the PM (a 6.9% decline) compared to the AM (a 3.5% decline).
Early sleep restriction (later bedtime) reduced performance by 5.9%, and PM exercise was impacted to a greater degree (a 6.2% decline) compared to AM exercise (a 1.6% decline). However, late restriction (earlier wake time) reduced performance by 7.4% — more than early sleep restriction. Similarly, early sleep restriction impacted PM exercise to a greater degree (a 9.7% reduction) than AM exercise (a 2.5% reduction).
Let’s give the above findings some context. It appears that while any type of sleep loss reduces performance, “achieving” sleep loss by waking up earlier seems to be much worse than going to bed later.
Why is this? It seems like the performance decline is linearly related to how much time you’ve spent awake! This meta-analysis also found that for every hour after waking up, performance declines by about 0.1%, and that increases to 0.4% if sleep loss occurs due to late restriction (an early wake time). This is why the combination of an early wake-up time and afternoon/evening exercise leads to the worst performance outcomes.
To use an example, someone who wakes up at 4 a.m. and completes a workout around 6 p.m. can expect a 5.6% decline in performance.
In other words, if you happen to find yourself in a situation where you’re sleep-deprived but still want to get a workout in, get started as early in the day as possible!
I’ve included the table of outcomes below, in which I’ve highlighted each performance outcome for easy locating. The performance change for each outcome can be found in the third column (also highlighted) as the “Mean” number, often presented as a negative (indicating a performance decline).
A few highlights.
Overall it seems that sleep loss has the greatest effects on reducing skill performance (21% decline), strength-endurance (9.9%), endurance (5.6%), HIIT (6.2%), and anaerobic power (6.3%), while strength and speed/power endurance are more resilient to sleep loss.
One interesting finding regarding strength performance was that, while lower-body strength appeared to decline after sleep loss, upper-body strength was unaffected.
A final reminder. Of course, these results reinforce that, for optimal performance, sleep is indispensable. But it’s worth noting that if you choose to sleep in that extra 1-2 hours and don’t get your workout in, performance declines by 100%
I’ve often sacrificed an hour or two of sleep to wake up earlier to sneak in a workout before a busy day of travel or festivities. Sometimes, a crappy workout is better than no workout at all. There’s always time for a nap later.🙂
Thanks for reading. See you next Friday.
~Brady~
Definitely early workout, coffees even if poor sleep or a late night. My workout feels like I am running on 3 batteries not 6. A arvo nap I didn't allow myself but now will :)