Background: Muscle weakness and obesity are two significant threats to mobility facing the increasing number of older adults. To date, there are no studies that have examined the association of strength and body mass index (BMI) on event rates on a widely used performance measure of major mobility disability.
Methods: This study was a secondary analysis of a randomized controlled trial in which sedentary functionally limited participants (70-89 years, Short Physical Performance Battery ≤ 9) who were able to complete a 400-m walk test at baseline were randomized to a physical activity or health education intervention and reassessed for major mobility disability every 6 months for up to 18 months. We evaluated whether baseline grip strength and BMI predicted failure to complete the 400-m walk test in 15 minutes or less (major mobility disability).
Results: Among N = 406 participants with baseline measures, lower grip strength was associated with an increased risk for developing major mobility disability, with and without covariate adjustment (p < .01): The hazard ratio (95% confidence interval) for the lowest versus high sex-specific quartile of grip strength was 6.11 (2.24-16.66). We observed a U-shaped relationship between baseline BMI and the risk of developing major mobility disability, such that the risk for participants with a BMI of 25-29 kg/m(2) was approximately half that of participants with BMI less than 25 or 30 kg/m(2) or more (p = .04 in fully adjusted analyses).
Conclusions: Our data highlight the importance of muscle weakness, low BMI, and obesity as risk factors for major mobility disability in older adults. Being overweight may be protective for major mobility disability.