Many sports-active people become involved in sports in order to compete, but others participate for different reasons - to lose weight, increase muscle size and strength, or preserve bone mass, for example. Running and cycling are two very popular sports, but it hasn't been clear which activity has the greater impact on body composition - until now.

Scientists at Columbia University in New York City recently checked the skeletons, fat deposits, and muscle characteristics of 14 highly trained male cyclists, 10 very fit runners, and 10 sedentary controls. All individuals were of similar weight (155 pounds) and age (27 years).

The runners had no advantage over the cyclists in body fatness; both groups checked in at 13-per cent body fat, significantly below the lard levels of the non-exercising controls (18 per cent). Total bone-mineral content was also similar between runners and cyclists.

However, the runners possessed about 6 per cent more bone mineral in their legs, compared to the cyclists, and 9-per cent more than the controls. Not to be outdone, the cyclists packed away bone mineral in their arms; runners and controls had 2-per cent skimpier arm-bone structures.

Runners also lost out on arm MUSCLE, which was 4 per cent below the mass achieved by both cyclists and sedentaries. Both runners and cyclists had about 10-per cent more leg muscle than the exercise abstainers.

The lessons? Compared to cycling, running represents a superior way to build up leg-bone density, an important effect when you consider that osteoporosis and leg-bone breakage is a common problem in elderly adults. Aside from that, running and cycling appear to have similar influences on body composition, with cycling tacking on a slightly greater amount of bony material in the arms.

('Distribution and Variation in Body Composition of Endurance-Trained Cyclists and Runners,' Medicine and Science in Sports and Exercise, vol. 26(5), Supplement, p. 573, 1994)