Arnold Schwarzenegger has long championed the value of sleep in building strength, often remarking: “You grow when you sleep, not when you train.” Professional athletes typically follow carefully structured sleep routines tailored to their chronotype — their natural preference for waking and sleeping — and aligned with their training demands.
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For most amateur athletes, however, the focus tends to lean towards nutrition and workout programming. Yet elite performance consultant Nick Littlehales, known for his work with top sports teams, has repeatedly argued that sleep deserves equal priority. “You can train as much as you like,” he says, “but without sleep, you’re not adapting — and without adaptation, there’s no progress.” Understanding what happens inside the body during sleep reveals why it should be considered a fundamental component of any performance strategy.
Sleep is far from a passive state. After a demanding training session, the body undertakes its essential restoration while we rest. Deep, slow-wave sleep is the critical phase during which tissues repair and regenerate. Protein synthesis works to mend the microtears created during exercise — the very cause of the DOMS many athletes recognise the next day.
This stage also triggers the release of human growth hormone (HGH), produced by the pituitary gland and vital for muscle repair, growth and overall recovery. Deep sleep strengthens immune function too, reducing the likelihood of illness that can derail even the best-planned training schedule.
Other crucial processes also unfold as we sleep:
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Glycogen stores are restored, and anti-inflammatory cytokines help soothe and repair fatigued muscles.
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Heart rate and blood pressure fall, giving the cardiovascular system a much-needed rest.
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Insulin sensitivity improves, supporting healthier glucose metabolism and more consistent energy levels.
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Hormones such as testosterone — essential for endurance and recovery — are regulated during sleep.
Physical recovery is only part of the story. REM sleep, which dominates the latter half of the night, allows the brain to carry out its own maintenance. Motor memory consolidation strengthens neural pathways established during training. The precise technique perfected during practice becomes firmly embedded during sleep. Emotional regulation also takes place during REM, helping athletes manage stress, maintain focus and stay motivated — key ingredients in achieving consistent performance.
The Swedish bedmaker Hästens takes the science of sleep seriously. Established in 1852, the company still handcrafts each bed in the town of Köping using only natural materials, with some models requiring up to 600 hours to make.
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Hästens has now launched its Sleep to Perform campaign, partnering with high achievers from the worlds of sport and the arts, including five-time Grand Slam champion Maria Sharapova. She credits restorative sleep as a cornerstone of her success. “Sleep is essential to performance regardless of where you are in your career,” she says. “It’s about more than rest — it’s about enabling yourself to be your best every single day.”
Whether amateur or elite, athletes share one universal truth: training does not end when the lights go out. In many respects, it’s only just beginning.
