Should you work out after a bad night's sleep?

You slept five hours. The alarm felt cruel. Your workout is on the calendar. Do you go?

Usually, yes, but lighter. Here’s how to decide, and what “lighter” actually means.

What one bad night does

One short night won’t wreck your strength. Most people can still lift close to normal. What changes is how hard everything feels, your focus and coordination, and how well you recover afterwards. Several short nights in a row are a different story: progress slows, and injury risk goes up.

So the goal after a bad night isn’t to skip. It’s to get the training in without digging a deeper hole.

A simple traffic light

Green: slept well, feel good. Train as planned. If you feel great, add one extra set to your first big lift.

Amber: slept badly or feel tired. Train, but lighter:

• About 30% fewer sets (4 sets become 3, 3 become 2).
• Nothing to failure. Leave an extra rep in the tank on every set.
• Keep the weights the same; cut volume, not quality.

Red: wrecked, several bad nights, or feeling ill. Make it a recovery day:

• Half the sets, two more reps in the tank, or
• a walk, mobility work and an early night instead.

If you have symptoms of illness (fever, chest symptoms, feeling unwell), rest. Training doesn’t help you fight off a cold.

Your watch can help you decide

If you wear an Apple Watch, Garmin, Oura or similar, three numbers are worth a look:

• Sleep duration against what you usually need.
• HRV (heart rate variability) compared with your own normal. A clear drop suggests your body is under strain.
• Resting heart rate compared with your normal. Several beats higher often means poor recovery, stress or something brewing.

The key is your own normal. Comparing your HRV with someone else’s tells you nothing; comparing it with your last two weeks tells you a lot.

Don’t forget how you feel

Wearables miss things: work stress, sore muscles, a heavy dinner. A quick honest check-in (great, good, tired, wrecked) is just as useful, and the two together are better than either alone.

Fix the next night

• Keep a regular bedtime, even at weekends.
• Last coffee or tea about 8 hours before bed.
• Dinner 2 to 3 hours before bed.
• Screens away 45 minutes before lights out.
• Get some daylight in the morning.

How Recomp handles it

Every morning Recomp turns your sleep, HRV and resting heart rate, plus a one-tap check-in, into a readiness score from 0 to 100. Above 80 you get an extra set; under 50 the session drops sets and nothing goes to failure; on a rough day it becomes a recovery session. You can try it on the home page.