In the United States, approximately 54 million people are impacted by osteoporosis and low bone mass,1 resulting in considerable public health and economic burdens. Osteoporosis, marked by reduced bone mineral density (BMD) and structural changes in bones,2 heightens the risk of fractures from minor injuries. Globally, each year, the direct costs of osteoporotic fractures are estimated to range from $5000 to $6500 billion across North America and Canada.3

Research indicates that low BMD, including osteopenia and osteoporosis, is disproportionately prevalent among individuals with disabilities.4,5 Studies have shown that more than half of women with physical disabilities experience low BMD, irrespective of menopausal status.6 Additionally, adults with acquired neurological disabilities face an elevated risk of bone loss compared to the general population.7

Although risk factors for low BMD, such as age, sex, race, body mass index (BMI), and physical activity, are well established in the general population,8 it remains unclear whether these same associations apply to individuals with mobility limitations. People with mobility disabilities often experience reduced or altered mechanical loading on bones due to decreased weight-bearing activity, neuromuscular impairments, or prolonged seated positioning. Research comparing athletes with disabilities to those without has shown that despite high physical activity levels, individuals with mobility impairments often have lower BMD in key skeletal regions. For instance, wheelchair athletes demonstrate lower bone mineral content compared to their ambulatory counterparts,9 and those with spinal cord injuries typically exhibit reduced whole-body BMD, even when physically active.10 Moreover, greater handgrip strength has been correlated with increased bone mineral content in people with spinal cord injuries,11 highlighting the role of mechanical loading patterns rather than total activity volume. These findings suggest that traditional protective factors like physical activity may not confer the same bone health benefits in mobility-limited populations. Therefore, this study seeks to examine whether adherence to physical activity guidelines and other established risk factors for low BMD are associated with total BMD in U.S. adults with mobility limitations.

While numerous studies have compared bone health between individuals with and without mobility limitations,4, 5, 6, 7,9, 10, 11 a critical gap remains in understanding the specific factors that influence BMD variation within the mobility-limited population. This study intentionally focuses exclusively on examining factors associated with BMD in adults with mobility limitations rather than comparing them to individuals without limitations. This approach allows us to identify risk and protective factors specific to this population, address the heterogeneity within the mobility-limited community rather than treating disability as a binary variable, and develop more targeted and appropriate bone health interventions.

The purpose of this study was to investigate the relationship between adherence to physical activity guidelines and total BMD among U.S. adults with mobility limitations, while also examining other potential risk factors, including demographic, anthropometric, and behavioral variables. It was hypothesized that individuals who met physical activity guidelines would have higher BMD than those who did not, but that the strength of this association might differ from patterns observed in the general population due to the unique biomechanical and functional characteristics of this group.