The Behavioral Rules

What you do during the day matters as much as what you do at night. Caffeine has a half-life of 5-6 hours, meaning half of your afternoon coffee is still circulating at bedtime.

Intense late-night training can leave some people too activated to fall asleep easily, but the effect is usually modest and individual. If hard evening workouts delay your sleep, move them earlier or finish with a longer cooldown. For many adults, moderate evening exercise does not harm sleep.