Grant: Operating Grant: Understanding the Health Impact of Inactivity

Inactivity increases fall and fracture risk, particularly in older adults. This may be due to bone and muscle weakness related to fat accumulation in bone marrow and muscles during inactivity as well as aging. We will test if exercise during 14-day bed rest can prevent or reduce inactivity-related fat accumulation in muscle and bone marrow and bone deterioration. We will assess if fat accumulation is linked to changes in muscle strength or bone properties. We will randomize 24 bed rest study volunteers (55-65 yrs) to an exercise group and control group. Both groups will have similar numbers of women and men. Exercise includes daily cycling and resistance exercises strengthening leg and arm muscles. We will use magnetic resonance imaging (MRI) to quantify muscle and bone marrow fat in the lower leg, hip and forearm prior to and after the 14-day bed rest and during recovery. We will measure muscle strength and function of the lower and upper extremities, and obtain measures of bone properties at the same time points. We will also obtain images using a new compact MRI prototype our group has designed for the International Space Station (ISS-MRI). We will test whether changes in bone marrow and muscle fat and bone porosity differ between exercise and control groups after bed rest and during recovery. We will also assess if observed differences are linked to muscle strength or function. We will test if changes alter between body sites or sexes. We will use MRI data to optimize the ISS-MRI. Study findings will reveal if fat accumulation and bone deterioration due to inactivity can be prevented by exercise and clarify mechanisms underpinning muscle weakness and injuries after inactivity. Findings will guide future research designs and strategies for effective exercise-countermeasures. This evidence can help in securing musculoskeletal health and mobility as well as prevention of falls and fractures after space travel or other periods of inactivity.