Sleep Quality and Exercise: Are You in the Dark?

A new study examined the effects of group exercise on the hormones that control sleep.

When it comes to sleep quality, many people are in the dark. Sleep is as necessary to life as food, water, and air, especially for athletes. In a study this month in the Journal of Strength and Conditioning Research, researchers examined the interplay between exercise and healthy sleep.

We all know that exercise is good for you, but some of the whys of the issue remain unknown. For example, exercise is one of the primary means by which the amino acid tryptophan enters the brain. Without exercise, this process won’t occur at optimal levels. I’m sure you’ve heard that it’s the tryptophan in turkey that makes you sleepy after a Thanksgiving meal. After being metabolized in the brain, some of the tryptophan you consume becomes melatonin, which was a hormone of major concern in this study.

Melatonin is the primary hormone that controls your circadian rhythm, which accounts for the cycle of sleeping and waking. Specifically, your melatonin is highest when it gets dark and lowest during the day. Having high melatonin at night is good, not only because it correlates directly to sleep quality, but also because it is a potent antioxidant that helps keep you healthy in numerous ways. With adequate tryptophan levels, you will also have good melatonin levels once night falls, and your sleep cycles should be normal and healthy.

In this study, the researchers examined a portion of the population known for poor sleep quality: post-menopausal women. Since melatonin declines with age, it’s no wonder the participants of the study tended to have sleeping problems. However, this study ought to apply to any population, especially people with sleeping problems.

The women were split into two groups. One group did an aerobics class for 45 minutes, three times per week, for ten weeks. The other group went about their normal business for the same period of time. Sleep quality was assessed via a questionnaire, and melatonin levels were measured before and after training.

The study was based on the effective of exercise on melatonin and sleep over time, rather than just a single session. For this reason, the researchers chose group exercise for the workout group, since working out in a group has been shown to improve adherence to a protocol and increase frequency of participation. The social aspect of group training is important, and may also allow participants to maintain higher degrees of intensity for longer.

Sure enough, exercise worked. On the questionnaire, the women in the exercise group reported significantly improved sleep compared the control group, whose sleep actually slightly worsened. Better yet, the melatonin levels of the training group increased nearly four-fold after the ten weeks, whereas the control group dropped by about half. Even in a population known for having sleeping problems, moderate exercise three times per week correlated with a major improvement in sleep quality – and, I daresay, improved overall health.


1. Zong-Yan Cai, et. al., “Effects of A Group-Based Step Aerobics Training on Sleep Quality and Melatonin Levels in Sleep-Impaired Postmenopausal Women,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000428

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