Axial Load during the Performance of Locomotor Training in Microgravity as a Factor of Hypogravity Countermeasure Efficiency

The physiological mechanisms that determined the maintenance of human physical performance in the absence of gravity are poorly understood. The article presents the results of analysis of locomotor training characteristics of 18 cosmonauts who participated in long-term spaceflights at the International Space Station (ISS) with the duration from 175 to 201 days. The level of cosmonauts' physical performance during spaceflight was determined by the results of a locomotor test with a stepwise increasing load. The vertical components of ground reaction forces were recorded for different types of locomotion using load cells in the BD-2 treadmill. The results of determination of changes in the level of cosmonauts' physical performance during long-term spaceflight have provided the data on a higher prophylactic efficacy of locomotor training performed with an axial load of over 64% of the body weight compared to those performed with an axial load of less than 61% of the body weight. The higher countermeasure efficacy of locomotor training in the first case may be due to an increase in the intensity of stimulation of the reference input and the strengthening of the response of systems providing autonomic muscle activity.