If you asked lifters or coaches which non-training factors are most important for lifters, most people would probably list nutrition and sleep as their top two choices.
However, we rarely write about sleep, not because we don’t think it’s important, but because there’s little longitudinal research on the topic. The reason for a dearth of longitudinal studies should be obvious: if a researcher asked you to participate in a 12 week training study, and they told you that you were only allowed to sleep five hours per night for the duration of the study, would you participate? I can quite confidently say that I would not volunteer for such a study. When it’s exceedingly challenging to recruit subjects for studies examining a particular research question, you won’t see much research tackling that specific research question.
However, there’s plenty of acute research investigating the impact of sleep duration on performance. I assume most readers wouldn’t be interested in a month-by-month account of every study investigating the impact of a single night of sleep restriction or deprivation on acute strength performance, but there is quite a bit of research on the topic. A recent meta-analysis by Craven and colleagues summarized this research (1), and I thought it might be of interest to readers for one major reason: sleep restriction and deprivation don’t seem to affect acute strength performance nearly as much as most people would suspect.
As with any meta-analysis, the researchers started with a systematic literature search. The studies included in this meta-analysis employed a repeated measures design (i.e., assessed performance before and after a normal night of sleep, and before and after sleep restriction or deprivation), were performed on healthy adult subjects, and assessed physical performance under both a sleep loss condition (≤6 hours of sleep in a 24 hour period) and a normal sleep control (>6 hours of sleep in a 24 hour period). Studies were excluded if the sleep loss intervention took place over multiple nights (since the researchers were interested in acute effects), if subjects were given stimulants or sedatives, or if the study was performed in populations with abnormal sleep behaviors (for example, people with sleep disorders).
After identifying the studies meeting these criteria, the researchers separated the studies based on the type of performance assessed in the study: anaerobic power performance, speed/power endurance, high-intensity interval exercise performance, endurance performance, strength performance, strength endurance performance, and skill-based performance. You can see descriptions of each performance category, and examples of performance tests that would fit into each category in Table 1. For the purposes of this research brief, I’ll mostly focus on strength and strength endurance performance.
From there, the researchers performed a series of meta-analyses quantifying the impact of sleep loss on each outcome. Furthermore, they performed sub-analyses investigating the effects of sleep deprivation (no sleep) versus sleep restriction (shortened sleep) on each outcome. When appropriate, they performed additional sub-analyses investigating the effects of early sleep restriction (going to bed late and waking up at a normal time) versus late sleep restriction (going to bed at a normal time and waking up early) on each outcome. The various types of sleep loss are illustrated in Figure 1. Finally, they performed meta-regressions to assess the relationship between time awake and reductions in performance. Of note, the researchers meta-analyzed percentage changes in performance, rather than computing standardized mean differences in the Cohen’s d family of effect sizes.
77 studies met the inclusion criteria, and were included in this meta-analysis. In total, these studies included 58 measures of anaerobic power, 32 measures of speed/power endurance, 27 measures of high-intensity interval exercise performance, 66 measures of strength, 22 measures of endurance, 9 measures of strength endurance, and 13 measures of skill-based performance.
Table 2 displays all meta-analysis outcomes. As you can see, sleep loss significantly reduced performance in all six categories.
Figures 2 and 3 show the impact of sleep loss on strength and strength endurance performance. Strength performance only decreased by 2.85%, on average, whereas strength endurance performance decreased by 9.85%. However, it’s worth noting that the strength endurance effect estimate was derived from just five studies, so it’s a relatively imprecise estimate.
Finally, there was a direct relationship between reductions in performance and time awake – the relationship was statistically significant for sleep restriction studies (p<0.001), and barely non-significant for sleep deprivation studies (p = 0.051). In other words, a night of poor sleep has a larger negative impact on performance in the evening than performance in the morning, and late sleep restriction has a larger negative impact on performance at a given time of day than early sleep restriction (i.e., if a performance test occurs at 3PM, a subject would have been awake for a longer period of time before 3PM following late sleep restriction than early sleep restriction). You can see this relationship in Figure 4.
Overall, this meta-analysis found that acute sleep loss does negatively impact strength performance, but the magnitude of that impact is fairly small. Furthermore, sleep loss seems to have a larger negative impact on strength endurance performance – one night of short sleep will probably have a larger negative impact on your 10RM strength and general volume tolerance than your 1RM strength. Finally, if you need to take one night of reduced sleep, it may be better to opt for early sleep restriction than late sleep restriction, if you’re given the opportunity to choose.
While the results of the present meta-analysis are straightforward, there are a few more factors to consider. First, it’s likely that the negative impact of sleep loss on strength performance increases following multiple nights of sleep loss. In other words, sleeping 5 hours one night may only reduce strength performance by ~3%, but sleeping 5 hours per night for a week straight is likely to reduce strength performance to a considerably greater extent (2). Second, we shouldn’t necessarily assume that a small effect on acute performance implies that consistent poor sleep will only have a small impact on hypertrophy and strength gains over time. There aren’t studies directly assessing the effect of consistent sleep long on muscle growth and strength gains, but I’ve consistently observed in my coaching practice that lifters make noticeably worse gains during prolonged periods of poor sleep. Finally, it’s likely that the negative impact of sleep loss on strength performance is affected by the degree of motor skill required for the exercise in question – one night of poor sleep may have a minimal effect on your biceps curl 1RM, but it may have a considerably larger impact on your squat 1RM, and an even larger impact on your snatch 1RM.
Note: This article was published in partnership with MASS Research Review. Full versions of Research Spotlight breakdowns are originally published in MASS Research Review. Subscribe to MASS to get a monthly publication with breakdowns of recent exercise and nutrition studies.
- Craven J, McCartney D, Desbrow B, Sabapathy S, Bellinger P, Roberts L, Irwin C. Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review. Sports Med. 2022 Jun 16. doi: 10.1007/s40279-022-01706-y. Epub ahead of print. PMID: 35708888.
- Knowles OE, Drinkwater EJ, Urwin CS, Lamon S, Aisbett B. Inadequate sleep and muscle strength: Implications for resistance training. J Sci Med Sport. 2018 Sep;21(9):959-968. doi: 10.1016/j.jsams.2018.01.012. Epub 2018 Feb 2. PMID: 29422383.