Association Between Muscle Strength, Mobility, and the Progression of Hyperkyphosis in the Elderly: The Kurabuchi Cohort Study

Background: The progression of hyperkyphosis is a significant factor in declining general health. The purpose of this study was to investigate whether muscle strength and/or mobility is associated with the progression of hyperkyphosis in elderly people. Methods: As part of a cohort study of community-dwelling elderly people, handgrip strength and mobility (evaluated with the Timed Up and Go Test: TUG) were assessed at baseline (2005-2006). Kyphosis was also evaluated at baseline and in follow-up examinations 4 years later, with the block method. To exclude the measurement error, the progression of kyphosis was defined as increase of 2 or more blocks. The association of kyphosis progression in each group with handgrip strength and/or mobility was assessed using Poisson regression analysis. Results: Results on 403 participants were available for the final analysis, and kyphosis progression was observed in 53 (13.1%) of them. Multivariable analysis adjusted for sex, age, baseline block number, bone stiffness, TUG performance, or handgrip strength simultaneously revealed that low handgrip strength (<26 kg in men, <18 kg in women) and low mobility (>13.5 seconds) at baseline were both independently associated with kyphosis progression (adjusted risk ratio [95% confidence interval]: 2.11 [1.06-4.20] and 2.48 [1.26-4.89], respectively). Conclusions: Our study showed that low handgrip strength and low mobility are clearly associated with the progression of kyphosis. Further study is needed on the applicability of these results to preventive measures.