Sleep & Exercise: A One-Way Relationship?

It’s a long-held reasonable assumption that sleep and exercise benefit each other. After all, sleep is restorative ready for exercise, and exercise tires you out ready for sleep.

Indeed, this forms at least part of a lot of circadian rhythm-based approaches to healthy living, for example:

10 Tips for Better Sleep: Starting In The Morning ← note though that the exercise timing advice here is “Exercise regularly but avoid strenuous activity 2 hours before bed. Optimal exercise time is 4–6 hours before bedtime.”

And yet, it turns out that the relationship is a lot more one-sided than has been believed:

You snooze, you… Choose? Enthuse? Put on your running shoes?

Researchers (Dr. Hannah Scott et al.) looked at data from 70,963 people (using an under-mattress sleep sensor and a wrist-worn health tracker) for a little over three and a half years, and found some surprising things, including:

• only 12.9% regularly attained the recommended seven to nine hours of sleep and more than 8,000 steps per day
• on the other end of the scale, 16.5% slept less than seven hours and walked fewer than 5,000 steps—an association with higher risks of chronic disease, weight gain, and mental-health challenges

However, putting the data together in a way we haven’t seen done before, Dr. Scott and her team were able to establish that there was more to this than “healthy people tend to be healthy in multiple life areas; unhealthy people tend to be unhealthy in multiple life areas”.

Specifically, six to seven hours of sleep was linked to the highest next-day step counts, though sleep quality remained most important. In other words, high-quality, efficient sleep (less tossing and turning) reliably predicted higher step counts the next day.

On the other hand, and which is more surprising, doing more steps during the day did not meaningfully improve sleep that night.

Putting it in numbers, we’ll quote directly from the “results” section of the paper:

❝We show that only 12.9% of people achieve the recommended sleep duration of 7-9hrs/night and >8,000 steps/day, with 16.5% having short sleep (<7hrs/night) and sedentary lives (<5,000 steps/day). Approximately 6hrs sleep equates to the greatest next-day step count (e.g., +339 steps vs 8 hrs/night), and sleep efficiency positively predicts next-day step count in a dose-dependent manner (25th vs 75th percentile: +282 steps/day). Sleep appears largely unaffected by previous-day step count. Effects are similar across age groups but decline in magnitude when adjusted for awake duration.❞

You can read the paper in full, here: Bidirectional associations between sleep and physical activity investigated using large-scale objective monitoring data

Note: curiously, and which doesn’t really affect the science here but we should found it interesting:

• Josh Fitton is the corresponding (and thus first-listed) author of the study, although he is a student, and
• Dr. Hannah Scott is Senior Research Fellow, NHMRC Emerging Leadership Fellow, and co-Lead of the Clinical Sleep Health research group at the Flinders Health and Medical Research Institute (FHMRI): Sleep Health Flagship program, and also has getting on for a hundred peer-reviewed papers to her name. Oh, and she’s the Chair on the Board of the Australasian Sleep Association (ASA): Australia’s peak sleep advocacy body. Aside from that, she’s received multiple awards including the Flinders University Vice-Chancellor’s Early Career Researcher Award, the ASA New Investigator Award and ASA Helen Bearpark Award, and the Society of Behavioural Sleep Medicine Fellow Rising Star Award. In short, she’s pretty cool and she knows her stuff.

Given that Dr. Scott’s research specialty involves investigating the use of digital technologies to better assess and manage sleep health and sleep disorders, we infer that Mr. Fitton is one of her students.

About those technologies, Dr Scott is also one of the researchers responsible for THIM: the first wearable device specifically to track and treat chronic insomnia.

On which note, you might want to check out: What Your Fitness Tracker Is Best & Worst At

Want to learn more?

For a particular kind of exercise that can help you sleep, you might like this book that we reviewed a while back:

Yoga For Better Sleep – by Mark Stephens

Sweet dreams!