Strain in the Proximal Femur during Neuromuscular Electrical Stimulation
Tom Abitante, HSL
Thursday, October 21, 2021
Astronauts in microgravity experience substantial bone loss which can pose a long term risk on future Lunar or Mars missions. Currently aboard the International Space Station, astronauts exercise as the primary countermeasure to reduce bone loss. While the current exercise regimen has been largely successful, it will not be able to be utilized on a future long duration spacecraft due to the volume, mass and power constraints. Additionally, exercise alone has not been able to fully replicate the daily loading the skeleton receives on Earth to sufficiently reduce the risk of fracture, despite 2 hours per day. Increasing the daily loading cannot be achieved by simply adding more exercise however. Excessive exercise increases energy expenditure, which can result in excessive negative energy balance, hindering efficacy. Therefore, non-exercise based methods of skeletal loading are required. Neuromuscular Electrical Stimulation (NMES) is a therapy where electrical pulses illicit involuntary muscle contractions. As the muscle contraction creates high forces on the bone, NMES presents itself as a possible disuse associated bone loss countermeasure. In order to predict the efficacy of NMES, the strain an isometric contraction induces on the bone must be modeled. The purpose of this study was to model the strain in the proximal femur during isometric contractions of the quadriceps and hamstrings, and to compare the strain to other activities such as walking and exercise. Strain can also be used to compute a daily strain stimulus, which is a measure of the total cumulative strain incurred over a given day, and can subsequently be used to determine regimen design and the dosing required for an osteogenic effect.