Abstract
The deleterious effects of spaceflight encompass numerous physiological effects that undermine long-term goals of manned round-trip missions to Mars. Among the greater losses are to the human musculoskeletal system due to limited mechanical/load-bearing activity. In-flight exercise and nutritional countermeasures seek to reduce physiological losses. Restoration of mechanical/load-bearing activity in microgravity is achieved with flywheel-based exercise hardware. Research with spaceflight analogs showed exercise done with flywheel-based devices abated muscle mass and strength losses with modest increases in net energy costs. This led to the installment of flywheel-based hardware on The International Space Station (ISS). To date, exercise with flywheel-based hardware has reduced musculoskeletal losses, with more success achieved for muscle-, versus bone-based, outcomes. In-flight exercise may better address bone losses with hardware that imparts high rates of impulse loading to the engaged musculoskeleton.