Enhanced dynamic load sensor for the International Space Station : design, development, musculoskeletal modeling and experimental evaluation

Abstract

Prolonged exposure of a vertebrate musculoskeletal system to the microgravity environment of space leads to a reduction in bone mineral density, muscle mass, strength and endurance. Such deconditioning may impede critical astronaut activities and presents an increased injury risk during flight and when exposed to increased gravity like that of Earth or Mars. Exercise countermeasures are used extensively on the International Space Station to mitigate musculoskeletal deconditioning during long duration spaceflight missions. Despite vigorous exercise protocols, bone loss and muscle atrophy are often observed even when countermeasures are in effect. As a first step in understanding the mechanisms of injury and how on-orbit exercise countermeasures compare to those on the ground, an accurate load sensing system is needed to collect ground reaction force data in reduced gravity.

To date, no means of continuous, high resolution biomechanical force data collection and analysis has been realized for on-orbit exercise. Such a capability may advance the efficiency of these systems in mitigating the incidence of bone and muscle loss and injury risk by quantifying loading intensity and distribution during exercise in microgravity, thus allowing for cause-effect tracking of ISS exercise regimes and biomechanics. By measuring these forces and moments on the exercise device and correlating them with the post-flight fitness of crewmembers, the efficacy of various exercise devices may be assessed. More importantly, opportunities for improvement, including optimized loading protocols and lightweight exercise device designs will become apparent.

The overall goal of this research effort is to improve the understanding of astronaut joint loading during resistive exercise in a microgravity environment through the use of rigorous quantitative dynamic analysis, simulation and experimentation. This is accomplished with the development and evaluation of a novel, self-contained load sensing system. The sensor assembly augments existing countermeasures and measures loads imparted by the crew during exercise. Data collected with this system is used to parameterize a unique musculoskeletal model which is then used to evaluate associated joint reaction forces generated during exercise. The effects of varying body posture and load application points on joint loading were investigated and recommendations for enhancing on-orbit exercise protocols that mitigate both injury and deconditioning are discussed.

By validating the sensor and modeling joint loading during on-orbit exercise as described herein, a unique contribution is made in expanding NASA's capability to continuously record and quantify crew loading during exercise on ISS. Data obtained through the system is used to characterize joint loading, inform and optimize exercise protocols to mitigate musculoskeletal deconditioning and may aid in the design of improved, lightweight exercise equipment for use during long-duration spaceflight, including future missions to Mars.