Running or cycling can be tough if you're overweight or suffer from joint problems or injuries, but that doesn't mean you have to lay off exercise altogether. Take your workout to the pool and you'll get the same aerobic benefit but with less wear and tear.
Researchers at the Montreal Heart Institute in Canada made healthy study participants do exercise tests on both land and water cycling machines (with water up to chest level). They increased their intensity minute by minute until exhaustion set in. It was found that the subjects' maximal oxygen consumption - which tells you whether it was a good workout - was almost the same using both types of cycles.
"If you can't train on land, you can train in the water and have the same benefits in terms of improving aerobic fitness," says Dr Martin Juneau, prevention service chief at the Montreal Heart Institute.
His study colleague Dr Mathieu Gayda, a clinical exercise physiologist, adds: "Exercise during water immersion may be even more efficient from a cardiorespiratory standpoint."
The researchers found that the heart rate of participants was a little lower in the water. "You pump more blood for each beat, so don't need as many heartbeats because the pressure of the water on your legs and lower body makes the blood return more effectively to the heart. That's interesting data that hasn't been studied thoroughly before," says Juneau.
In the book Advanced Marathoning, authors Pete Pfitzinger and Scott Douglas note that deep-water running with a floatation vest is a total-body exercise that works your legs, trunk and arms, and positively stresses your cardiovascular system. Several studies have verified that runners can use deep-water running to maintain aerobic fitness, lactate threshold, running economy and time-trial performance for at least six weeks.
A useful rule of thumb, write the authors, is that heart rates during water running are about 10 per cent lower than during land running. For example, if you get your heart rate up to 140 beats per minute in the water, that's roughly equivalent to 156 beats per minute during normal running.