Thursday, November 18, 2010

Soccer Training and Bone Health

We have known for years that exercise is good for bone. This is especially true for women. We also understand that some types of exercise are better than others. Bone responds to the stress and mechanical loading of exercise. Thus, weight bearing and resistance types of exercise have greater effects on bone density and bone strength than non-weight bearing activities. What about soccer? Does soccer, a weight bearing exercise improve bone health? A new study from Clermont University in France addresses this question. Researchers show that yes, soccer can be very beneficial for bone health.

The study focused on adolescent female soccer players and swimmers (average age of 16 years). Both groups of athletes practiced for about 10 hours per week over the course of a 36-week season. Measures of bone density and size were performed and the results were compared to a group of healthy, non-athletes. All three groups were similar in terms of age, height, weight and percent body fat.

Regardless of the site measured (whole body, spine or hip), the soccer players had the highest bone mineral density (BMD). Swimmers and control subjects had similar values. More importantly, the geometry of the bone was changed in the soccer players. Bone is composed of a dense “outer shell” called the cortex. Inside the cortex is either a hollow region filled with bone marrow (where red blood cells are produced) or a region filled with less dense or spongy bone called cancellous tissue. In the hip region, the soccer players had a denser and thicker cortex. This was true for the shaft of the femur (long bone of the leg) and the neck. Also, the neck of the femur was larger in diameter. These differences make for a much stronger bone in the soccer players. This is especially important for the hip. Most hip fractures occur in the neck region. So, improving the BMD and strength of this part of the hip should lower the risk of fractures.

If exercise is good for bone and both groups of athletes exercise on a regular basis, why do the soccer players have better bone health? The answer to this question lies in the stress that swimming and soccer place on the bone. Bone is continually “turning over” or remodeling itself. It does this through the processes of deposition (growth) and resorption (breakdown). When bone encounters stress, it responds by increasing the rate of deposition and decreasing the rate of resorption, especially in the areas that are stressed. Thus more bone is formed. Running, starting, stopping, cutting and jumping during soccer training all place a considerable amount of stress on the bone. This mechanical load stimulates growth and increases the density of the cortex. On the other hand, swimming is a non-weight bearing or hypogravity activity. The only major forces placed on the bone are from muscle contractions. The lack of stress during swimming fails to stimulate bone growth to the same extent as soccer. That is not to say that swimming isn’t a good form of exercise. On the contrary, joint injuries and fractures are far less common in swimming than soccer and swimming certainly develops cardiovascular fitness. But in terms of bone health, this new research study shows that soccer is far superior.

What about calcium intake? Interestingly, the swimmers had a higher calcium intake that the soccer players. Yet, they had lower BMD. We’ve known for years that calcium intake is very important for bone health of females. Is this not the case? Both the soccer players and swimmers had adequate calcium intake – none of the athletes were deficient. The researchers suggest that with adequate calcium intake, calcium alone is not able to stimulate additional bone growth. Exercise, more importantly weight bearing exercise, is needed to improve bone health. While calcium intake remains an important part of a healthy diet, exercise is also critically important for the bone.

Do the effects of soccer on bone health have long-term benefits? This is a very good question that doesn’t have a definitive answer. However, some insight can be gained through a series of studies conducted on retired female gymnasts. As expected, gymnastics training has a remarkable effect on bone density. Due to the amount of stress gymnasts encounter during training, they have some of the highest BMD of all athletes. Interestingly, gymnasts who have been retired from competition for as long as 24 years still maintain higher BMD than non-athletic women. This is the case even if the gymnasts are inactive during retirement. Somehow, they are able to retain this benefit of training. Given this, it is very likely that the positive effects of soccer training on bone health may carry over into adulthood.

The bottom line, this new study shows that soccer training in teenage girls has positive effects on bone health. It appears to increase bone growth, density and alter the geometry of the bone. These changes likely translate into stronger, healthier bones.

Reference:

Ferry B, Duclos M, Burt L, Therre P, LeGall F, Jaffre’ C, Courteix D (2010) Bone geometry and strength adaptations to physical constraints inherent in different sports: comparison between elite female soccer players and swimmers. Journal of Bone and Mineral Metabolism. DOI: 10.1007/s00774-010-0226-8