Jeff, I trust & follow your advice most of all, but what if, in this case, I played devil's advocate a little with the interpretation?
Those curves are interesting. It's nice to see that walking doesn't have a negative-parabola shaped pattern like running. As for running, even if running "dosage" exhibited symmetry (a worst-case scenario I would think), it wouldn't cross the walking curve until ~65 minutes a day, or 455 minutes of running a week, or, say, 56 miles a week at an 8:00 pace. So you wouldn't be worse off than a walker until you hit around 56 miles per week of running, which is a high amount of vigorous activity. (8 miles a day every day on average.) And you would be better off as a runner until then.
The text of the latest study is interesting. The claims seems to be that increased doses are not associated with increased benefits (after a certain threshold). Perfectly reasonable. Walking seems to approach a limit of 35% reduction in mortality. Given the language in the papers, though, it sounds like they aren't super willing to assert that there are serious
detriments to lots of physical activity. And, since exercise has other benefits besides lowering mortality (e.g. burning calories), I would think there is no serious reason for most people to limit it unless it's at a really high amount.
Exercise is Medicine at Any Dose? wrote:Increasing from the minimum effective levels of moderate (15 minutes a day) or vigorous intensity (8 minutes a day) physical activity to the national physical activity guidelines of 30 minutes a day of moderate-intensity exercise or 75 minutes a week of vigorous intensity exercise appears to be associated with increased health benefits. Every additional 15 minutes of moderate-intensity physical activity was associated with a 4% further reduction of all-cause mortality over 13 years in the Taiwanese population.
These benefits were independent of age, sex, and cardiovascular history. The greatest benefit was obtained by the most active individuals (63-88 minutes a day), with higher mortality reductions for vigorous-intensity vs moderate-intensity exercise.
Similar findings were observed in US and European cohorts. Individuals performing physical activity at a dose of 3 to 5 times the current recommendations reported the lowest mortality rates over 14.2 years.