Is Your Evening Workout Costing You Sleep?

Picture from Sitnsleep.com

I read that the Kenyan runners usually ran at least twice a day. The first run when it's still dark between 6 to 630 am to beat the heat. It is usually an easy progressive run though sometimes long runs or fartleks can take place. 

A second session often takes place between 10-11 am. This is usually reserved for track interval sessions. Typically they do 2-3 key interval sessions a week with most of the runs really easy so they can recover. When asked why they do the second run before lunch, the reply is so that they have more time to recover before the next day's sessions. 

Sometimes they even do a lighter recovery run between 4 to 5 pm to add to their weekly mileage.

So I was not surprised when I read that the timing of our workouts can affect our sleep (Akhtar and Eleftheriou, 2026). To avoid confounding factors, sleep and activity data from the same day through a model with fixed effects and terms for activity time, activity-sleep gap and the interaction between these terms. 

Data collected from users sleep looked at how sleep was affected by when they decide to exercise. The focus was on cardiovascular exercises, specifically walking, running (outdoor and treadmill), cycling (outdoor and stationary) and hiking. They studied over 100,000+ workout sessions and found that the later you train, the worse you recovered (pictured above).

When you exercise later in the day, your sleep heart rate is higher, your heart rate variabilty (HRV) is lower and you get fewer REM sleep events. You may sleep quicker with later workouts, but it is not better sleep. It is falling asleep faster while recovering less.

The benefits plateau around the 10 hour mark. The sweet spot is a 11 to 14 hour gap between your workout and bedtime. If you can exercise earlier in the day, you can capture most of the benefits. Perhaps that's the reason the Kenyan runners do their second run at 9 am. 

What about those people who can only exercise at 8pm onwards or later? Should you worry about this?  My take is no. Majority of people should NOT worry. I think it is more important to exercise where it fits in your life. 

Don't worry too much about HRV scores or perfect recovery. You are only working out at 8 pm or later because that's the only time when family and work gives you an opportunity to. Many people do not have the luxury to choose the time to exercise and exercising at any time is better than no exercise.

Our bodies are remarkably adaptable too. I am sure if you exercise at 8 pm or later long enough your body will get better sleep. Not perfect sleep but the detriment is less.

Showing up and exercising is way more important than perfect conditions. Consistency beats optimization every time. That is what will compound.

Reference

Akhtar F and Eleftheriou K (2026, May 24). Your Evening Workout Is Costing You Sleep. Terra API. Https://trryterra.co/research/best-time-toworkout--for-sleep#the-honest-takeaway