July 14, 2023 -- For as long as we’ve had official recommendations for exercise, those recommendations have focused on effort.
Do at least 150 minutes a week of “moderate to vigorous” physical activity, public health guidelines say. That could be anything from brisk walking (moderate) to competitive mountain-bike racing (vigorous).
But as broad as that spectrum is, it still leaves out a lot. Like washing dishes. Or changing a diaper. Or birdwatching in the park. Or giving a PowerPoint presentation.
All those tasks are “light” physical activities. We don’t think of them as exercise, and public health guidelines don’t account for them.
But at least one researcher believes we should take them more seriously.
“Light physical activity appears to be the key to almost universal success regarding health,” said Andrew Agbaje, MD, a clinical epidemiologist at the University of Eastern Finland.
The High Cost of Not Moving
Any parent, teacher, or caregiver can tell you that children slow down as they age. A kid who was bouncing off walls at 11 may move very little at 24. But it's not necessarily their fault.
“We are more or less forcing them into sedentary behavior,” Agbaje said, pointing to things like school, homework, and all the other situations that require kids to sit still. Their free time, in turn, increasingly involves screens, which keep them sitting even longer.
“We’re playing with a time bomb,” Agbaje said.
In a recent study of nearly 800 children, Agbaje measured how the children’s activity changed between the ages of 11 and 24.
Several findings stand out:
- The kids’ moderate-to-vigorous activity was unchanged over time. It was about 60 minutes a day for males and 45 minutes a day for females at 11 and 24 years old.
- Light physical activity declined by about 3.5 hours a day.
- Sedentary behaviors — sitting, sleeping, or otherwise barely moving — increased by almost 3 hours a day.
- C-reactive protein increased significantly from age 15, when it was first measured, to 24. It nearly doubled in males and tripled in females.
While sedentariness was strongly linked to rising C-reactive protein, activity at any intensity was associated with lower inflammation.
But here’s an interesting wrinkle: The more body fat participants had, the less effective physical activity was in fighting inflammation. Body fat reduced the benefit of moderate-to-vigorous activity by close to 80%.
That wasn’t the case for light physical activity. Body fat mitigated just 30% of the benefit.
“Light physical activity looks like an unsung hero, which is surprising and new,” Agbaje said. “We might need to focus on that in this generation.”
The Time-Intensity Continuum
That said, there are good reasons for public health guidelines to focus on higher intensities.
Take, for example, a study of Swedish military conscripts who underwent a battery of fitness tests in the early 1970s, when they were 18. Four decades later, those who had the highest exercise capacity in their late teens were 19% less likely to have subclinical levels of arterial plaque, meaning the levels of plaque in their arteries were not detectable by typical medical tests.
Exercise capacity, as you might guess, is the maximum amount of continuous exertion your muscles and cardiovascular system can support. Higher capacity is usually the result of higher-intensity exercise.
“The relationship between physical activity and exercise capacity is bidirectional and dynamic,” said study author Melony Fortuin-de Smidt, PhD, a postdoctoral researcher at Umea University in Sweden.
In other words, what you can do now reflects what you did in the past, and what you do now will affect what you can do in the future — for better or for worse.
That’s not to say you can’t get the same benefit from lower-intensity activities. But there’s a catch: “You will need to do more,” Fortuin-de Smidt said.
In another recent study, Fortuin-de Smidt and her co-authors calculated that you’d need 60 minutes of walking at a “normal” pace to get the same reduction in cardiovascular disease risk as you’d get from 40 minutes of brisk walking.
But those figures “should be interpreted cautiously,” since they include self-reported data, she said.
A 2019 study that used data from activity trackers came up with starkly different estimates: to get maximum protection from the risk of early death, you’d need 24 minutes a day of moderate-to-vigorous activity or 6-plus hours of light activity -- “15 times longer to reap the same mortality benefits,” Fortuin-de Smidt said.
Notably, that study includes an in-between category the authors call “high” light physical activity. That could include low-intensity yoga or calisthenics, cooking or cleaning, and shopping or gardening. For those activities, you’d need just 75 minutes a day to get the same health benefits as 24 minutes of moderate-to-vigorous activity.
It’s worth mentioning that any of those activities could also be regular light or even moderate-to-vigorous, depending how quickly or slowly you do them. Intensity is not about the activity type – it’s about the effort you put into doing it.
When Light Makes Right
The message here isn’t to obsessively categorize every movement into vigorous, moderate, “high” light, or regular light. Most of our activities probably include some combination.
The goal is to take more steps.
“Every move and every step counts towards better health,” Fortuin-de Smidt said.
Agbaje compares exercise to medicine. Each of us needs to adjust the exercise dose to fit our needs, goals, and abilities.
A tough workout for an average adult might qualify as a warmup for a well-trained athlete, while the athlete’s warmup might be dangerous for someone who’s not prepared for it.
That, Agbaje said, is the best argument for moving more whenever possible, even if it doesn't feel like exercise.
“For everybody, light physical activity is safe,” he said. “Just go for a walk.”