The Harvard study also indicates a maximum exercise window: approximately three hours of vigorous activity or six hours of moderate-intensity activity per week.
“Doing higher activity level is perfectly fine, it is just that no additional health benefits would be gained further,” Hu says. “One who can run marathons everyday may not have a lower risk of dying than people who do regular brisk walking.”
The biological mechanisms behind this are unclear. Some experts theorize that overworking your body may increase chronic inflammation or arterial stiffness, both which have been shown to increase risk of cardiovascular disease.
“We need more data, especially from clinical trials, to examine associations of different types of exercise on various health outcomes,” Lee says.
Why exercise variety is key
Interestingly, Hu’s study found that regardless of how much a person worked out, variety improved participants’ longevity. When it came to reducing risk for cardiovascular disease, respiratory disease, or cancer, the most diverse exercise group had 13 to 41 percent lower risk compared to the least diverse group.