150 minutes a week. That’s the minimum recommended amount of moderate-intensity exercise the federal government advises the American people to do to optimize their health.
150 minutes a week. That number wasn’t pulled out of thin air. There is a bunch of observational data that shows that people who are more physically active have better health outcomes. Those who hit that 150 minute-a-week mark have around a 30% reduction in overall mortality rates, even when you control for health status at baseline.
But only about half of Americans actually get that much exercise, as you can see here, with younger people doing better than older people, and men getting a bit more exercise than women.
How do you get more people to exercise? Maybe you need to make it easier.
Part of the reason a lot of people miss the exercise target is that 150 minutes just seems daunting. The physical activity guidelines suggest that these 150 minutes be “spread throughout the week”. But not all of us have 30 minutes a day, Monday through Friday to take a brisk walk on a treadmill, or a jog around the block.
Could it be good enough to hit the weekly target all at once?
The agreed-upon scientific term for this behavior — doing all your weekly exercise in one or two big sessions — is the “Weekend Warrior” pattern. And, in this week’s JAMA Internal Medicine, a large study asks whether Weekend Warriors are as protected from death as people who spread their exercise more evenly.
The study leverages more than 350,000 responses to the US National Health Interview Survey — which is representative of the population at large. The researchers, led by Yafeng Wang, merged that survey data with the National Death Index, which captures date and cause of death for all deaths in the US.
What do weekend warriors look like?
In the JAMA-IM study, compared to those who exercise regularly throughout the week, weekend warriors were younger, more likely to be male, less likely to be white, have a lower level of education and a lower overall income level. I think this speaks a bit to the idea that the ability to have 30 minutes a day to exercise is a marker of privilege. Not everyone has jobs with that kind of schedule, or the childcare to allow 30 minutes of “me time”.
The authors seem to recognize this, leaving BMI out of their primary analysis, but including an adjustment for BMI in a sensitivity analysis.
But the lesson of BMI might apply to some of the factors they adjusted for in the primary analysis too. Might exercise actually decrease smoking rates? Or alcohol intake? If so, these might be on that causal pathway from exercise to survival — not something we’d want to adjust for.
So we need to look at that final estimate of benefit — 15% reduction in mortality — with a bit of a skeptical eye. The true number could be quite a bit higher. It could probably be lower too.
Of course, physical activity, as a medical intervention, has just about the best risk : benefit ratio you could imagine. The message of this paper, underneath all the epidemiology and statistics is a simple one — get some exercise, whenever you can. It’s good for you.
