| dc.description.abstract | During spaceflight, astronauts experience bone loss, in part, due to the absence of the skeletal loading normally experienced on Earth. The current ISS exercise regimen is not expected to sufficiently reduce the risk of fracture on a long duration mission to Mars (>6 months) and additional exercise cannot be added as exercise is time consuming, incurs high caloric demands, and future spacecraft will be unable to accommodate the current machines. Therefore, to minimize the risk of musculoskeletal related injuries, additional skeletal loading should be introduced via non-exercise based countermeasures. The purpose of this research is to examine the potential efficacy, practicality, and potential implementation of Neuromuscular Electrical Stimulation (NMES), a therapy that induces involuntary contractions of muscles, to help mitigate astronaut bone loss as a result of microgravity.
To accomplish this, we first produced a finite element analysis model of the femur, to determine the strain at the proximal femur during NMES contractions of the thigh muscles. This strain was compared to the strain produced during other activities that have been investigated for bone loss in order to infer efficacy. Second, we examined how healthy individuals, and subsequently different muscle characteristics, produce force and fatigue with NMES in order to inform both initial and progressive regimen design. Last, we performed a metabolic analysis, examining the metabolic cost of repetitive NMES to the thighs and lower legs, and comparing this cost to that of walking at various speeds. Determining the potential caloric cost of a NMES therapy will aid in determining feasibility as well as regimen design.
The results of this research show that NMES can create strains at the proximal femur comparable to simple, non exercise activity like that of walking. The bouts of repetitive contractions would need to initially be a maximum of 5 to 10 minutes in duration in order to minimize fatigue and maximize the force of each contraction, and would incur only a modest caloric expenditure, minimizing the risk of a negative caloric balance when used as a supplement to exercise. Over the course of the day, hundreds of loading cycles could be added to the femur, as well as the tibia, increasing the skeletal loading, further reducing bone loss, and subsequently reducing the risk of fracture upon landing on Mars. | |
