Globe and Mail
Monday, Oct. 04, 2010
As a form of regular aerobic exercise, swimming has lots of benefits. It uses large muscle groups, can be maintained continuously for long periods of time, and is easy on lower-body joints because it doesn’t involve bearing body weight. But research on the health-promoting effects of swimming is surprisingly sparse – and some studies now suggest that a half-hour of swimming may not provide the same benefits as a half-hour of comparable land-based exercise.
The problem is that your body gets a fundamentally different physiological challenge from being horizontal in water compared with being upright on dry land, thanks to the hydrostatic pressure and high thermal conductivity of water, according to Hirofumi Tanaka, director of the University of Texas’s Cardiovascular Aging Research Laboratory.
Dr. Tanaka reviewed current evidence for swimming’s effects on cardiovascular health in the journal Sports Medicine last year. He found solid evidence that regular swimming improves control of blood-sugar levels in the body, which reduces the risk of diabetes.
But several studies have found that swimmers tend to have higher blood pressure than other endurance athletes. A 2006 study by researchers at the University of Western Australia found that blood pressure actually increased in a group of sedentary older women after a six-month swimming program, possibly because water pressure keeps peripheral blood vessels more constricted than usual during exercise.
But several other studies have not observed the same effect – and there’s similar disagreement about whether swimming raises or lowers “good” HDL cholesterol.
The temperature of the water can also make a big difference. University of Florida researchers found that swimmers consumed 44 per cent more calories after exercising in water at 20C than in water at 33C, which may explain why many studies have failed to find weight-loss benefits from swimming regimens.
The conclusion Dr. Tanaka draws from this rather confusing picture is that we can’t assume that different forms of exercise produce exactly the same benefits.
Swimming is great for muscles, joints and some (but not all) cardiovascular risk factors. But to get the full array of possible benefits from aerobic activity, you might want to include some land-based exercise in your routine at least once or twice a week.