Walking would be a good start (1), but there are more effective alternatives (2) which cyclists might consider (3), although I'm not sure if being sarcastic has any added benefits; perhaps you could let us know?
1) From the American
NIH Osteoporosis and Related Bone Diseases National Resource Center:
"The best exercise for your bones is the weight-bearing kind, which forces you to work against gravity.
Some examples of weight-bearing exercises
include weight training,
walking, hiking, jogging, climbing stairs, tennis, and dancing. Examples of exercises that are not weight-bearing include swimming and bicycling. Although these activities help build and maintain strong muscles and have excellent cardiovascular benefits, they are not the best way to exercise your bones."
2) From
The University Of Arizona:
"
The best exercises for building bone are weight- or load-bearing exercises. These include weight-lifting, jogging, hiking, stair-climbing, step aerobics, dancing, racquet sports, and other activities that require your muscles to work against gravity. Swimming and simply walking, although good for cardiovascular fitness, are not the best exercises for building bone."
3) From
About.com:
"Swimming and bicycling are not considered weight-bearing exercises and aren't usually listed on the list of exercise that increases bone density. In fact, there is some evidence that elite level cyclists actually lose bone density during high intensity training and racing.
Several studies, including
one in 2008, found lower bone density in elite level cyclists who train for hours on the bicycle.
Researchers are not entirely sure the cause of the bone loss in cyclists, but the current theories include:
- The non weight-bearing nature of cycling put little strain magnitude (see above) on the bones.
- Minerals, including calcium, are lost at an enormous rate during hours of sweating.
- The possible energy imbalance (more calories are used than consumed) during hours of intense exercise."