Simulation Strategy to Enhance Oxygen Uptake and Reaction Forces at Leg Joints and Vertebral Bodies During Ergometer Exercise Under Altered Gravity

Abstract

Moderate exercise has been implemented in spaceflight programs to prevent muscle and joint damage under extreme circumstances such as microgravity. Although the physical effects of exercise have been investigated experimentally, advanced modeling and simulation techniques are powerful tools that could provide insight into the physical limitations, optimal conditions, and mechanisms that might lead to muscle and joint damage. Ergometers are safe for patients and elderly individuals because exercise intensity can be easily regulated. Moreover, ergometer exercise that removes the load imposed by body weight on leg joints would better reflect training conditions in locations such as the International Space Station or on the surfaces of the Moon and Mars, where the force of gravity is lower than that on the Earth. A hybrid training system (HTS) that combines the electrical stimulation of antagonist muscles and volitional contraction of agonist muscles is an effective training method. Co-contractile motions in the HTS can counteract the reduced effect of gravitational force on leg joints during ergometer exercise. The present study aimed to validate the ability of an ergometer exercise model to measure oxygen uptake and joint reaction forces by comparison with experimental results and create strategies for electrically stimulating leg joint muscles for modulation under altered gravity. The simulation results suggested that the HTS could easily control the magnitude of oxygen uptake and joint reaction forces. Optimal cycling conditions to achieve desirable values for oxygen uptake and joint reaction forces would help to maintain the health of astronauts and appropriate exercise programs could be implemented in constrained space facilities.