It is widely recognized that exercising contributes to overall good health. But too much of it can also have adverse effects, particularly insulin resistance similar to that caused by diabetes.
The many benefits of exercise are numerous: prevention of cardiovascular disease, improving sleep, reducing the risk of diabetes, weight control, combating arthritis and osteoporosis, not to mention mental health benefits. But excessive exercise also carries risks, as shown in a study published in Cell Metabolism. According to the authors of the study, excessive exercise could affect the metabolism of cells, leading to a dysregulation of glucose uptake.
Dysregulation of metabolism
Mikael Flockhart and his colleagues at the Stockholm School of Sport and Health recruited 11 volunteers and subjected them to increasingly intense cycling exercises for four weeks. During the experiment, they measured their glucose tolerance, cardiovascular capacity, and mitochondrial function through muscle biopsies.
Although the athletes’ performance and physiological parameters initially improved, things began to go awry after the fourth week, during which the athletes were subjected to a particularly high tempo (152-minute intensive training sessions). During this week, mitochondrial respiration, which is used to produce ATP that provides energy to cells, decreased by 40%. “An impaired mitochondrial function leads to a reduced ability to respond to nutrient supply and to align mitochondrial respiration with metabolic demand,” explains Filip Larsen, lead author of the study. In addition, the volunteers’ glucose tolerance (measured by their glucose levels before and after consuming a sugary drink) also decreased dramatically.
Excessive exercise health risks
After a recovery phase, subjects were, fortunately, able to partially restore their original functioning, but not completely, with glucose tolerance remaining 25% lower after recovery than after the week of moderate exercise. Can intense sport promote diabetes? It might, as it has already been shown that excessive exercise can have harmful effects. “Other studies have shown that intense exercise has negative effects on heart health, including increased coronary artery calcification, myocardial fibrosis, and cardiac arrhythmias,” the authors say. Excessive exercise also increases the risk of injury and may lead to a form of addiction (bigorexia).
However, it is unclear where the line is drawn between when exercising is beneficial and when it begins to have harmful effects. Top athletes are generally a very healthy group,” Larsen says. Also, exercising too little is a more common problem than exercising too much.”
Still, most people who exercise will most likely never do it excessively, and as such, the results of this study should really not worry them.