Trunk muscle strength, but not trunk rigidity, is independently associated with bone mineral density of the lumbar spine in patients with Parkinson's disease

Previous literature suggested that muscle forces applied to the skeleton may be an important factor in increasing bone mineral density (BMD). This purpose of this study was to determine whether trunk rigidity and trunk muscle strength were associated with lumbar spine BMD in patients with Parkinson's disease (PD). Forty-three PD patients and 29 controls participated in this study. Dual-energy X-ray absorptiometry was used to measure lumbar spine BMD of PD patients. Additionally, an isokinetic dynamometer was used to evaluate trunk rigidity and trunk muscle strength of all subjects. The results showed that PD patients had significantly lower trunk muscle strength, but more trunk rigidity than controls by 46.6 and 162.8%, respectively (P < 0.001). In bivariate correlation analysis, lumbar spine BMD was significantly related to trunk muscle strength (r = 0.475, P = 0.001), but not trunk rigidity (r = 0.271, P = 0.079). In multiple regression analysis, after adjusting for relevant factors, only trunk muscle strength remained independently associated with lumbar spine BMD, accounting for 10.0% of the variance (R(2) = 0.342, F(5,) (37) = 3.838, P = 0.007). Trunk muscle strength, but not trunk rigidity, is independently associated with lumbar spine BMD in patients with PD. Further randomized controlled studies are required to determine whether trunk muscle strengthening exercise is effective in enhancing lumbar spine BMD.