Estimating lower limb joint internal loading during locomotion and plyometric movement and their relationship to simulated hypogravity: in vivo data to inform in silico analyses

Prolonged exposure to hypogravity is associated with deconditioning of the musculoskeletal system, such as bone mineral density loss, muscle atrophy and muscle weakness, which may present operational risks to astronauts on the Moon and Mars during locomotion and candidate exercise countermeasures. Therefore, the quantification of the internal (i.e. joint contact and muscle forces) and external (e.g. ground reaction forces) loads experienced by the musculoskeletal system in hypogravity are critical to predict the magnitude of musculoskeletal deconditioning and its related risks. The quantification of such forces is particularly relevant druing locomotor and ballistic movements, as it can to inform the requirement for exercise countermeasures. Although the external load experienced by the musculoskeletal in simulated hypogravity has been estimated for a number of locomotor tasks, very little is known about the corresponding internal loads directly experienced at the joint, muscle, muscle- tendon and bone level. Closing this is gap is critical as it is the internal, rather than external, forces that drive musculoskeletal adaptations and thus must be preserved to maintain homeostasis.
Therefore, we propose to i) measure in 20 participants: full body kinematics, external load, lower limb muscles activation, and the calf muscle-tendon behavior during locomotion and maximal plyometric activities in 6 simulated hypogravity (1G, 0.75G, 0.5G, 0.38G, 0.25G, 0.17G) levels, and ii) estimate the corresponding lower limb muscle and joint reaction forces using musculoskeletal modelling created and validated by our team.
Thus, we require the unique ground-based facility in Milan (L.O.O.P.) as it allows the capture of such data, during both locomotion and maximal plyometric exercise under high-fidelity variable simulated hypogravity.