How Muscles Affect Bone Health

In general, by maintaining proper muscle balance and by being healthy and properly trained, you can significantly reduce the risk of bone problems, the most common one in endurance athletes being stress fractures. Should you have a stress fracture, healing occurs much more rapidly if you have better muscle balance and are healthier overall. Of course, many stress fractures occur due to muscle imbalance interfering with weight bearing, gait, and other movement.

Stress fractures are usually less severe than most other bone problems, but can significantly interfere with training and racing. While some occur from simple trauma—a bike crash, for example—others occur from repetitive overuse or a sudden increase in activity. In some cases, metabolic causes are evident, such as in female athletes with amenorrhea (the lack of a normal menstrual period), which is associated with hormone imbalance affecting bone strength, or due to osteoporosis in either sex. While the bones in the legs (tibia and fibula) are common sites of stress fractures, they can also occur in the foot’s metatarsal and navicular bones, the bones of the pelvis, and many other bones.

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Pain from a stress fracture typically improves with rest and worsens with activity. There is often some swelling in the area, but sometimes it’s not noticeable. The swelling around the site of fracture may prevent a proper diagnosis by X-ray if taken within the first two weeks of injury. Only after some healing has taken place will the X-ray show the problem. In these situations, a bone scan may help locate the stress fracture when the X-ray can’t.

Most stress fractures will heal well in a healthy person without major therapy. Rest, cooling the site of fracture, cessation of weight-bearing exercise, and hard-soled flat shoes are often sufficient, but each case must be treated individually. Aspirin and other NSAIDs must be avoided as they can delay bone healing.

Just as important is the fact that something caused a stress fracture to occur; and that something—some imbalance in muscles, hormones, diet, or often a combination of problems—must be found and corrected. If this does not happen, the athlete is vulnerable to future fractures.

A low-fat diet may be associated with a higher incidence of stress fractures—statistically more in female athletes. Fats are important for many aspects of health, with certain fats helping to carry calcium into bones (and muscles). Bone health is related to more than just calcium: zinc, vitamin K, and many other nutrients, including protein, are also very important for bone health—all factors that a healthy diet provides. Vitamin D may be the most important nutrient for bones and our most important source is from the sun.

Surprisingly, the importance of muscle function in bone health is often not discussed, but it may be the most important contributing factor in stress fractures. In addition to muscle imbalance, which can cause reduced support and increased stress on specific areas of the skeleton, reduced muscle mass is associated with reduced overall health, including nutritional and hormone imbalance, making the bones vulnerable, too. Low muscle mass also physically reduces bone support, especially when the aerobic muscle fibers are not well developed.

And while we often discuss the negative aspects of excess physical stress, too little physical stress can also be a problem. Those who don’t regularly perform gravity-stress-related exercise may be more at risk for bone problems. Endurance athletes in general don’t have this problem, but if you’re a swimmer, and don’t perform any other workouts such as walking or running, the gravity stress on your body may be less than optimal. In some cases, even cycling can result in significantly less gravitation stress on the body than running or even walking. In these instances, cross-training can be very helpful Athletes who are fit and healthy dramatically lower their risk of stress fractures, along with other injuries.