Does Exercising Later In The Day Affects Your Ability To Sleep?

Zzz after a hard ride ...

I've written before in a previous post that I'm a poor sleeper. If you're like me, when I pushed myself too hard at training, I actually found it harder to fall asleep. The more I need (and want it), the harder it is for me to get it.

And sleep you know is critical for your mental and physical well being. If you're athlete, sleep is the easiest and cheapest intervention you can utilize to help your performance.

Hence, I was quite intrigued when I saw work from researchers who tested the effects of whether morning or evening workouts will affect your sleep by measuring melatonin levels. Melatonin is a hormone secreted in the pineal gland that regulates sleep and wakefulness.

Melatonin levels start to rise around your bedtime. It helps to lower your body temperature (now you know why it's so hard to fall aslleep when it's been so hot recently) and a rise in sleepiness. Melatonin levels usually peak around 3 am for most people.

The volunteers in the study were tested on three different days. A day with no exercise, a day when they exercised at 9 am or another at 4 pm. Their workout was a 30 minute  run at 75 percent VO2 max. Melatonin levels were measured with a saliva test at 8 pm, 10 pm and 3 am.

The results showed that those who did the 4 pm exercise session had much lower melatonin levels at 10 pm and 3 pm compared to the 9 am exercise group. It means that those who exercised in the afternoon (or those of you who can only train after work) will have a tougher time falling and staying asleep. End of story, period?

Not really. Don't worry if you're like most other Singaporeans who mostly have time to train only after work hours.

Melatonin is just one part of the equation in your quest to fall and stay asleep. Melatonin levels may not be the main reason why you cannot fall asleep.

For you to get a good night's sleep, it may depend on what you you eat/ drink, the wavelength of light emitted by your smart phone, the temperature of your room, your exercise routine/ intensity and not just your workout time rather than just your melatonin levels.

If you're going for a "relaxing" evening run, and clearing your head over stresses you've encountered during the day, it's gonna be a lot easier than doing sprint intervals. Although some runners may even say that the intervals make them tired and thus make them sleep better. This alone may be far more important than melatonin levels.

Another factor that is not addressed in the paper by the authors is whether genetically you are a "night owl" or a "lark"? The New York Times has a good article on how there's a strong basis on a person's natural inclination with regards to the times of day when they prefer to sleep or when they're most alert.

Some of you reading this now (after exercising late in the day and not sleeping) are likely to be "owls" and not likely to get up early to exercise since you sleep later. This may may due to your circadian wiring rather than exercise timing. So shifting your exercise timings to the morning may "rob" you of your morning sleep without helping you to fall asleep earlier.


Reference

Carlson LA, Pobocik KM et al (2018). Influence Of Exercise Time Of Day On Salivary Melatonin Responses. Int J Sp Physiol Perform. 30: 1-13. DOI: 10.1123/ijspp.2018-0073.

*Picture by Jeremy Ong