Lifters are told to sleep more, but how much does a bad night actually cost you in the gym? A systematic review in the Journal of Science and Medicine in Sport pulled together the evidence.
What the review found
The review included 17 studies, rated as moderate or weak in overall quality. One night of sleep deprivation had little effect on muscle strength during resistance exercise. In contrast, several consecutive nights of sleep restriction could reduce force output in multi-joint movements such as squats and presses, but not in single-joint movements. Findings on hormonal responses to resistance training were conflicting.
The conclusion
The authors concluded that inadequate sleep impairs maximal strength in compound movements when no specific interventions are used to raise motivation. They suggested that people short on sleep may cope better by boosting motivation, for example by training with others.
What this means for lifters
- A single bad night is unlikely to wreck a workout. Do not skip training for it.
- Repeated short nights are the bigger risk for heavy compound lifts.
- Keep sleep regular. Recovery, appetite and mood all depend on it, even though the strength studies are limited.
- On low-sleep days, a training partner or a clear plan can help effort.
See our workout nutrition guide for the fuelling side of recovery.
Frequently asked questions
Does one night of bad sleep reduce strength?
The review found sleep deprivation had little effect on muscle strength during resistance exercise.
Which lifts are affected by poor sleep?
Consecutive nights of sleep restriction could reduce force output in multi-joint movements, but not single-joint movements.
Can I train when I am tired?
The review suggests motivation matters, so training with others or using a clear plan may help you maintain performance.
References
- Knowles OE et al. (2018). Inadequate sleep and muscle strength: Implications for resistance training. J Sci Med Sport. PubMed 29422383
General information, not medical advice. Check with a doctor before starting a new training routine. Last updated 28 October 2026.
