Several studies have shown that road cyclists who spend more than six hours per week in the saddle may be at risk for low bone mass, particularly in the lower spine. Researchers point out three main reasons for this, a few of which apply to mountain bikers as well:
1. Cycling is not a weight-bearing activity.
In healthy people, bone responds to stress by laying down new bone to strengthen itself against similar stress in the future. According to a paper recently published on bone health in endurance athletes, high-impact activities performed in multiple planes, like the movements used in ball sports (think jumping, changing direction) are more effective at increasing bone mass than repetitive, long-duration activities performed in a single plane, like road cycling, swimming, and running. In a seated position on a road bike, the lower back is minimally activated, which is not helpful for building or maintaining bone density.
However, mountain bikers may be off the hook on this one. A study published in 2002 comparing the bone density of mountain bikers to that of road cyclists found the off-roaders had significantly higher bone density in their entire bodies than road cyclists, likely because the vibrations endured while mountain biking stimulate bone growth.
2. Cyclists can lose calcium through sweat.
Clearly, mountain bikers are not immune from this issue. Researchers believe that an exercise-induced increase in parathyroid hormone can negatively affect bone density. The parathyroid hormone regulates calcium levels in the blood and may be released in response to calcium lost through sweat. If the parathyroid hormone senses calcium levels are low, it will raise them by liberating the mineral from bones.
Researchers have found that taking 1,000mg of calcium 20 minutes before exercise may block the body from leaching the mineral from bones, but the effectiveness of taking calcium supplements is still under investigation.
3. Cyclists don’t eat enough.
While mountain biking may help build bones, following the “eatin’ is cheatin’” mantra of some elite cyclists can set you up for low bone density and its consequences, including stress fractures and osteoporosis. Not eating enough calories can interfere with your body’s ability to build and maintain bone mass.
It’s been suggested that endurance athletes eat a minimum of about 20 calories per pound of body weight per day, or 3,200 calories per day for a 160-pound person. If think you may be underfueling, see a nutritionist, or start logging your food and exercise to make sure you’re eating enough to maintain your bone density.
THE BOTTOM LINE: Mountain bikers may more easily build and maintain bone mass than road cyclists because of the vibrations endured cycling off-road. But poor nutrition on and off of the bike could counteract those positive gains.