How does sleep deprivation affect your workouts?

Sleep is one of those topics where the advice seems obvious: get more of it. But how much does missing a few hours actually hurt your gym performance? Can you still train effectively after a bad night, or is it better to rest and recover? Let’s look at what the research says.

First, we need to establish what actually happens when you get a bad night’s sleep. Sure, working out can feel worse, but how does a bad night’s sleep impact your performance objectively?

A recent meta-analysis by Craven et al examined 69 studies with 227 outcomes on how acute sleep loss (≤6 hours of sleep in a 24-hour period) affected exercise performance.
The authors categorized exercise tasks into seven types:

• Anaerobic power
• Strength and strength-endurance
• Speed/power endurance
• Endurance
• Skill-based tasks
• High-intensity intervals
  

Across almost every category, sleep loss impaired performance. The biggest decline was seen in skill-based tasks: things requiring fine motor control, coordination, or precision. In contrast, strength and power performance were affected a fair bit less, but still consistently dropped.

While this finding was relatively robust, the magnitude of the effect is worth noting. On average, for every hour participants were awake before training, performance declined by roughly 0.4%. That doesn’t sound dramatic, but missing several hours of sleep can feel like it adds up. For example, if you get only 4 hours of sleep before a workout, you could expect to be around 2-3% weaker that day – roughly the difference between hitting your usual last rep or failing the set a rep early.

Interestingly, though, not all sleep loss was equal. The pattern of sleep restriction matters.

Total sleep deprivation – think an all-nighter – or late-night restriction tended to hurt performance the most.

On the flip-side, early restriction – think waking up earlier than usual, but going to bed at the usual time – had a smaller impact.

Likewise, the time of day that training took place seemed to matter. Workouts done in the evening after poor sleep suffered more than morning sessions, likely because fatigue and sleep pressure accumulated throughout the day. So, if you have to train after a bad night, an early session might be the lesser evil.

Similarly, if you have some work you need to get done ASAP, this suggests you’d be better off waking up early to get some work done than going to bed late to finish it off. Training early might help too.

Given the positive impacts of exercise on sleep duration and quality, it’s usually worth getting a workout in, even after a bad night’s sleep, though you may find it easier to do so by reducing difficulty a bit.

But fundamentally, what gives? Besides feeling dreadful, why does one night of bad sleep impact workout performance?

A review by Fullagar et al suggests there are likely a few factors that contribute:

• Increased sympathetic and reduced parasympathetic activity, resembling early overreaching.
• Glycogen repletion can be impaired after severe sleep deprivation.
• Slightly increased inflammation.
• Cognitively, slower reactions, worse decision-making.
• Reduced motor memory consolidation.

To close us out, here are a few practical takeaways on how sleep deprivation impacts your workouts and how to adjust your approach:

• Acute sleep loss does reliably negatively impact workout performance
  • However, this is a larger effect for skill-based tasks vs strength and power.
• One bad night won’t make-or-break anything.
  • A single night’s poor sleep may lower performance, but it’s unlikely to blunt long-term adaptations if your overall sleep is decent.
• Prioritize recovery after sleep loss.
  •  If possible, shift harder sessions to another day or reduce load slightly.
• When training sleep-deprived:
  • Opt for morning workouts if your schedule allows.
• If you have the choice:
  • Opt to go to bed at your usual time but wake up early. This pattern appears to compromise performance a bit less.

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