The Associations Between Muscle Function, Physical Performance and Fall Injuries in Older Adults

Background: Weight-bearing measures of lower-extremity muscle mechanical function may be more strongly related to physical performance and fall injury than non-weight-bearing measures in older adults. However, these relationships are not well-described since past studies have typically not included multiple muscle function and physical performance measures, or non-fracture fall injuries. Objectives: This dissertation examined associations of (1) multiple muscle function measures (lower-extremity muscle power and strength, and grip strength) with physical performance, (2) novel jump test measures (jump power, velocity and force) and grip strength with physical performance, and (3) baseline leg power and grip strength with incident fall injuries (non-fracture and fractures). Methods: Study populations included community-dwelling older adults from the (1) Developmental Epidemiologic Cohort Study (N=68; age=78.5±5.5 years; 57% women), (2) Osteoporotic Fractures in Men (MrOS) Study clinic visit 4 (N=1,242 age=84±4 years), and (3) MrOS baseline clinic visit with fall injury follow-up data (N=5,994; age=73.7±5.9 years). Multiple regression analyses with standardized βs were applied to objectives 1 and 2; generalized estimating equations with unstructured correlation were applied to objective 3. Results: First, jump power and grip strength had higher magnitudes of association with faster gait speed than the other power or strength measures, a magnitude of association with faster 400m walk time that was similar to Keiser power and higher than other power and strength measures, and a lower magnitude of association with chair stands speed than any other power or strength measures. Secondly, lower power and velocity were associated with slower gait speed, longer 400m walk time and slower chair stands speed, whereas force and grip strength were more weakly associated with physical performance. Finally, both lower leg power and grip strength were associated with increased fall injury risk. Conclusion: These findings suggest that muscle function impairments are related to physical performance, including mobility, and fall injuries in older adults. Future studies should examine longitudinal associations of muscle function changes with changes in geriatric outcomes related to physical performance, mobility and falls. The public health relevance of current findings is that identifying potential earlier muscle function predictors of disability may inform prevention efforts that would ultimately reduce disability incidence