You’ve heard the advice: "Don't exercise before bed, it will keep you awake."
But you’ve also heard: "Exercise makes you sleep better."
So, which is it?
The relationship between sweat and sleep isn't linear. It depends on timing, intensity, and body temperature. Here is how to design your workout schedule to maximize your nightly recovery.
The Core Mechanism: The Thermal Drop
Sleep is triggered by a drop in core body temperature. Exercise does the opposite—it heats you up.
If you do a high-intensity interval training (HIIT) session at 9 PM, your core temperature might remain elevated until midnight, physically preventing your body from initiating sleep.
The Rule: Finish vigorous cardio at least 3 hours before bed.
Aerobic vs. Resistance: Which is Better for Sleep?
A 2022 study presented at the American Heart Association made waves: Resistance training (lifting weights) might be better for sleep than cardio.
- Aerobic Exercise: Great for reducing anxiety and burning energy, but raises cortisol significantly during the activity.
- Resistance Training: Increases Adenosine (sleep pressure) buildup in the muscles without the same massive cortisol spike as sustained cardio.
Participants who lifted weights added an average of 40 minutes of sleep per night.
The "Late Night" Myth
What if you can only exercise at night?
Don't skip it. The benefits of exercise outweigh the risks of arousal. However, you need to modify the type of exercise.
- Go: Heavy lifting, yoga, steady-state walking.
- No-Go: Sprinting, CrossFit, competitive sports (adrenaline).
Recovery Metrics: HRV
How do you know if you are overtraining? Your sleep data holds the answer.
Heart Rate Variability (HRV) is the variation in time between heartbeats.
- High HRV: Your nervous system is balanced and recovered.
- Low HRV: Your body is stressed and in "fight or flight" mode.
SleepMo Insight: If you see your HRV drop significantly on the SleepMo dashboard after a late workout, your body is telling you it didn't get enough time to cool down before sleep. Push your workout 1 hour earlier next time.
Conclusion
Movement is medicine for sleep. It burns off cortisol and builds adenosine.
But respect the thermodynamics. Give your body time to cool down. If you must train late, lift heavy things slowly rather than running fast. Your deep sleep score will thank you.