"Associations of Muscle Function and Size with Falls, Fall Injuries, and Bone Density, Microarchitecture, and Strength in Older Adults", Public Health/Epidemiology. 

Committee: 

• Elsa S. Strotmeyer, EPI (chair)
• Jane A. Cauley, EPI
• Kristine M. Ruppert, EPI
• Bradley C. Nindl, Department of Sports Medicine and Nutrition

Abstract:

Background: Falls and poor bone health increase the risk of fractures, which affect 1 in 3 women and 1 in 5 men aged >50 years globally. Identifying modifiable risk factors, such as muscle function and size, is essential for reducing fracture burden in aging. However, few studies have included multiple measures of muscle function and size to determine which predict falls/fall injuries and bone health. 
Objectives: This dissertation examined associations of (1) grip strength and stair climb power with recurrent and injurious falls longitudinally; (2) grip strength and jump power with longitudinal changes in bone density, microarchitecture, and strength using high-resolution peripheral quantitative computed tomography (HR-pQCT), and (3) whole-body muscle mass and thigh muscle volume with HR-pQCT measures cross-sectionally. 
Methods: Participants included: (1) women from the Study of Women’s Health Across the Nation (N=1719, age 65±3 years), (2) men from the Osteoporotic Fractures in Men Study (N=225, age 83±3 years), and (3) women and men from the Study of Muscle, Mobility and Aging (women: N=181, men: N=118, both aged 76±4 years). Generalized estimating equations estimated longitudinal odds of recurrent and injurious falls, while multivariable linear regression examined associations with bone parameters.
Results: Higher grip strength, but not stair climb power, was associated with lower odds of injurious falls, but not recurrent falls, in middle-aged and older women (6.6±0.3 years follow-up). Higher grip strength, but not jump power, was associated with changes in tibial bone area in older men (6.2±0.6 years follow-up). Cross-sectionally, greater whole-body muscle mass was associated with higher bone strength in older women, but not men, while greater thigh muscle volume was associated with higher bone strength in both sexes. 
Conclusion: These findings identify higher grip strength as a predictor of lower fall injury risk and bone adaptation, supporting its utility as a simple and practical measure of muscle function in aging populations. Sex-specific associations between muscle size and bone strength highlight the need for further research into muscle-bone interactions in populations of both women and men. These results may guide musculoskeletal interventions targeting muscle strength and size to reduce the public health burden of falls and fractures.