Does Intensity of Physical Activity Matter?

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Volume 16, Number 12

          There is extensive evidence indicating that regular physical activity is beneficial for health. While there is less clarity about what type and how much exercise is optimal, a common starting point is that the most important physical activity for a given individual is that which the individual is willing and able to do on a regular basis. At the most basic level, some is better than none.

            Of course there are recommendations for how much physical activity adults should get. The Centers for Disease Control and Prevention (CDC) recommendation is at least 150 minutes per week of moderate intensity aerobic activity and at least 2 days each week of muscle-strengthening activity that involves all major muscle groups. Less “officially,” a goal of 10,000 steps per day is often mentioned.

            In March 2020, a study was published in JAMA indicating that all-cause mortality was reduced for individuals attaining 8000 steps per day compared to those getting 4000 steps per day. There was some additional reduction in mortality for those reaching 12,000 steps per day, but this additional benefit was not as great as it was for the increase from 4000 to 8000. The nearly 5000 participants in this study wore accelerometers, so in addition to the number of steps taken, step intensity was measured. One of the conclusions of the study was that after adjusting for the number of steps, step intensity did not convey any additional benefit.

            Fast forward to November of this year. An investigation that examined the physical activity of over 400,000 US adults was published in JAMA Internal Medicine. In this study, intensity of exercise did matter. Those adults whose total physical activity contained a greater proportion of vigorous physical activity were found to have lower all-cause mortality. This study was based upon self-report of exercise, in which moderate physical activity was defined as causing “only light sweating or a slight to moderate increase in breathing or heart rate” and vigorous physical activity was defined as causing “heavy sweating or large increases in breathing or heart rate.”

            With respect to these two studies, one reported that step intensity doesn’t matter, while the other study concluded that getting vigorous physical activity does matter with respect to all-cause mortality. It is important to note that the methods in these studies were different, even though all-cause mortality was the primary outcome of interest.

            Considering these two studies along with many other studies examining the health benefits of exercise, and keeping in mind that all research has limitations, it is reasonable to draw some working conclusions. Certainly, some is better than none as a starting point. Meeting the aforementioned CDC guidelines through moderate physical activity is associated with substantial health benefits. However, there do appear to be additional and incremental health benefits associated with more exercise and with increasing the proportion of one’s exercise that meets criteria for vigorous activity. What is less clear is how much is too much, although that issue is not a relevant concern for the majority of US adults.

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