There are currently a record number of middle-aged Canadians taking part in high endurance sports, like ultra-marathons and long-distance cycling.

Training for these kinds of events, however, often results in long-term physiological changes for athletes, and new research suggests that some of these changes can be unhealthy – even dangerous.

About five per cent of middle-aged people who significantly exceed the recommended 150 minutes of weekly exercise experience side effects such as irregular heart rhythm, which can lead to blood clots and strokes.

Interestingly, conditions related to ultra-endurance training appear to be more common among men.

Check out the report from CBC's Kim Brunhuber to learn more about the athletic craze gaining popularity across the country, and what it means for athletes' bodies.