Striated Muscle Evaluation Based on Velocity and Amortization Ratio of Mechanical Impulse Propagation in Simulated Microgravity Environment

SIMPLE SUMMARY: Long-duration space flight missions impose extreme physiological stress and changes on the crew due to the microgravity exposure. The herein study was performed by using MusTone, a device developed by the Institute of Space Science, to understand the influence of microgravity physiological stress on striated muscles and to provide countermeasures that are able to minimize the negative effects of weightlessness on musculoskeletal function. The results emerged following a statistical analysis performed on the data collected from six subjects engaged in a 21-days Dry Immersion (DI) experiment. Two parameters of muscles’ fibers behavior in the longitudinal direction were extracted and analyzed (i.e., propagation velocity and amortization ratio). It was confirmed that muscle deconditioning is time-dependent and also that, as muscle exposure to Dry Immersion increases, the amortization ratio increases and is more significant in the distal position. Moreover, muscle deconditioning occurs in a gradient: it starts first in distal points and affects more the distal muscles, those which are involved in posture maintenance and have an antigravity role. The results are important when taking into account space tourism developments, as long as astronauts and space tourism candidates will require a reliable real-time and non-invasive method able to quantify the muscle dynamic changes. ABSTRACT: Long-duration space flight missions impose extreme physiological stress and/or changes, such as musculoskeletal function degradation, on the crew due to the microgravity exposure. A great deal of research studies have been conducted in order to understand these physiological stress influences and to provide countermeasures to minimize the observed negative effects of weightlessness exposure on musculoskeletal function. Among others, studies and experiments have been conducted in DI analogue Earth-based facilities in order to reproduce the weightlessness negative effects on the human body. This paper presents a complex muscular analysis of mechanical wave propagation in striated muscle, using MusTone, a device developed in-house at the Institute of Space Science, Romania. The data were collected during a 21-day DI campaign in order to investigate muscle fibers’ behavior in longitudinal direction, after applying a mechanical impulse, taking into account two particular parameters, namely propagation velocity and amortization ratio. The parameters were determined based on the wave-propagation data collected from five points (one impact point, two distal direction points, and two proximal direction points) along the muscle fiber. By statistically analyzing propagation velocity and amortization ratio parameters, the study revealed that muscle deconditioning is time dependent, the amortization ratio is more significant in the distal direction, and the lower fibers are affected the most.