Qingju Wang, Markku Alen, Patrick Nicholson, Harri Suominen, Arvo Koistinen, Heikki Kroger, Sulin Cheng
The mechanical environment is considered to be the most important determinant of bone strength. Local muscle force, in turn, is regarded as the largest source of loading applied to bones. However, the effect of weight-bearing on bone mineral accrual is unclear, therefore this relationship is examined in this study.
The 258 healthy girls aged between 10â€“13 years old had their bone mineral content (BMC), lean body mass (LM) and fat body mass (FM) of total body assessed by dual-energy X-ray absorptiometry at baseline and 2 years after. Using a dynamometer, the maximal isometric voluntary contraction (MVC) of left elbow flexors and knee extensors was evaluated and a linear statistical model with random effects was used to analyze the relationship between the BMC and limb-matched MVC. The authors used Fisher's z-transformation to compare the correlation between the arms and legs and Student's t-test to compare the ratio of BMC to MVC in the upper and lower limbs.
BMC was highly correlated with MVC in arms and legs (r2 = 0.54 and 0.50, respectively), and the correlation did not differ between upper and lower limbs. However, BMC/MVC was significantly (30%) higher in leg than in arm. Therefore the results indicate that local muscle contraction and weight-bearing exert an additive effect on bone mass accretion in the lower limbs and in growing children exercise regimes combining both resistance and impact training should provide larger bone response, than either one alone.
Bone, 2007 40(5), 1196-1202