If you exercise more than this amount of time per day, the results are disastrous

Few medical professions would argue against the health benefits associated with habitual exercise. However, a growing body of research is beginning to shed light on the consequences linked to overexertion.

In a new paper published in the journal Cell Metabolism, researchers at the Swedish School of Sport and Health Sciences determined that excessive exercise can impair several important cardio-metabolic functions.

The researchers gauged metabolic efficiency via a model called intrinsic mitochondrial respiration.

“Here, we used a training model with a progressively increasing exercise load during an intervention over four weeks. We closely followed changes in glucose tolerance, mitochondrial function and dynamics, physical exercise capacity, and whole-body metabolism. Following the week with the highest exercise load, we found a striking reduction in intrinsic mitochondrial function that coincided with a disturbance in glucose tolerance and insulin secretion,” the authors wrote in the new paper.

“We also assessed continuous blood glucose profiles in world-class endurance athletes and found that they had impaired glucose control compared with a matched control group.”

Unfortunately, there isn’t a canonized value that indicates too much exercise for the general public. The relevant factors principally correspond with health goals, medical history, weight, diet, and age.

Having said that, the new study revealed that there is a point at which the benefits awarded by routine exercise begin to plateau before eventually causing more harm than good. For the sake of this analysis, the researchers defined over-exertion as high-intensity exercises that exceed 152 minutes, cumulatively.

The participants began with 36 minutes of high-intensity intervals segmented over the course of 7 days. A moderate week then followed, which included 90 total minute intervals.

Cardio-metabolic function improved exponentially for all of the participants during these intervals.

From the report:

“Exercise training positively affects metabolic health through increased mitochondrial oxidative capacity and improved glucose regulation and is the first line of treatment in several metabolic diseases.”

During the third week, which was meant to represent excessive training intervals (intense bouts of physical activity performed for 152 minutes), the subjects’ intrinsic mitochondrial respiration fell by an average of 40%. This group also evidenced decreased glucose tolerance.

“It’s quite similar to the changes that you see in people that are starting to develop diabetes or insulin resistance,” the authors added.

“All athletes know if you train too much, something’s happening. . . . Your legs feel terrible after a while, and then if you just continue, you have these psychological disturbances too, like mood disturbances. That hasn’t been really described in the literature—no one knows exactly what’s going on.”

One 52 minute recovery restored most of these measures for all of the subjects. Though, their intrinsic mitochondrial respiration did not fully recover by the end of the study period.

On balance, this particular metabolic health measure remained 25% lower after recovery than it had been following the moderate week intervals.

In order to confirm the results of the first leg of experiments, the researchers recruited 15 elite athletes before comparing their glucose response to a control group comprised of non-athletes.

The two groups’ glucose levels over a given 24-hour period were about the same, even though the athletes spent significantly more time with glucose levels either above or below the normal range.

“I think joining together those findings gives a really strong message of the impact of exercise training on glucose tolerance,” the authors concluded in a media release.

Most health officials recommend adults try to exercise for at least 30 minutes a day.