MRI scans showing a stress fracture of the sacrum, a bone at the base of the spine.

Under strain

Extreme exercise can be harmful

Doing an exercise programme on top of an active lifestyle can have costs – it can make you tired or cause injuries. Injuries can occur when people exercise inappropriately (eg when lifting weights the wrong way), so it might be wise to get instruction and coaching and to allow your body to adapt slowly to new forms of exercise. Muscle sprains, muscle strains and stress fractures in bones often affect athletes whose sport requires continual repetitive effort, such as tennis players.

Simple wear and tear is a risk for joints, which bear a lot of the strain of different forms of exercise. Habitual runners work their knees hard, and running has previously been linked to arthritis in later life. More recent reviews, however, suggest that it is harmless at worst and might even be good for the joints in the majority of people. Running after a knee injury or while overweight does appear to be harmful, though, and weightlifters and football players have both been found to suffer from arthritic knees in later life. Football can be particularly damaging because of the twisting and turning of the knee involved.

Another general effect of very frequent and intense exercise shows up in the immune system: doing exercise seems to boost the immune response, but overdoing it can have the opposite effect. Intense exercise – for example, a marathon – appears to make athletes more susceptible to infections like colds and sore throats. Part of the reason is the release of the hormone cortisol, which helps us cope with stress by boosting glucose use, but also damps down immune reactions and reduces inflammation.

There is also evidence that long-term endurance exercise can do harm to the heart. A study of men who had earned admission to the 100 Marathon Club found that the older among them had some heart muscle scarring. More research is needed to understand the implications of this finding, however.

Lead image:

Magnetic resonance imaging (MRI) scans showing a stress fracture of the sacrum, a bone at the base of the spine.

Wellcome Images CC BY NC ND


About this resource

This resource was first published in ‘Exercise, Energy and Movement’ in January 2012 and reviewed and updated in August 2016.

Physiology, Health, infection and disease
Exercise, Energy and Movement
Education levels:
14–16, 16–19, Continuing professional development