High-intensity indoor cycling classes carry a "significant risk of kidney damage" – especially for first-time participants – according to a report in the American Journal of Medicine.

The study claims that indoor cycling classes – which simulate climbing hills, cycling on flat roads and include sprint cycles – may result in rhabdomyolysis.

Rhabdomyolysis is a condition where severe muscle trauma – due to a lack of oxygen – causes muscles to break down and release their contents into the bloodstream.

The syndrome, typically found in victims of a crush injury – such as a result of a car crash – can lead to serious complications, including kidney failure.

"Risk factors for the development of rhabdomyolysis are related to the intensity of the exercise, the conditioning of the participant, hydration, and body temperature, in addition to other potential contributing factors," the report says.

"Physiology studies have demonstrated that significant numbers of calories are burned, fluid losses are significant and body temperatures increase during indoor cycling classes."

The study presented details of three "unusual cases of exertional rhabdomyolysis", each occurring in a patient who had taken part in their first indoor cycling class.

In the first case, rhabdomyolysis developed following 15 minutes of a class. In the second case, it occurred in a young individual who exercises regularly. In the third case, the patient developed "biopsy-proved acute kidney injury" secondary to exertional rhabdomyolysis and required hemodialysis.

As a result of the study, the authors – a team from the Westchester Medical Center in New York, US – recommended a set of guidelines for indoor cycling to be set up.

"The only way to prevent rhabdomyolysis from indoor cycling is to have safety guidelines set up," the authors write in the report.

"Beginners need to know how to gradually increase the time and cadence on the indoor cycle.

"They need to be made aware of the importance of staying hydrated and the need to avoid nonsteroidal anti-inflammatory drugs. Participants need to be informed of the risks of rhabdomyolysis.

"Guidelines should include information about the signs and symptoms of rhabdomyolysis and the urgency of seeking hospital treatment when such manifestations occur."

To read the study in full, click here for the American Medical Journal website .