Effects of exercise countermeasures on multisystem function in long duration spaceflight astronauts.

Exercise training is a key countermeasure used to offset spaceflight-induced multisystem deconditioning. Here, we evaluated the effects of exercise countermeasures on multisystem function in a large cohort (N = 46) of astronauts on long-duration spaceflight missions. We found that during 178 ± 48 d of spaceflight, ~600 min/wk of aerobic and resistance exercise did not fully protect against multisystem deconditioning. However, substantial inter-individual heterogeneity in multisystem response was apparent with changes from pre to postflight ranging from -30% to +5%. We estimated that up to 17% of astronauts would experience performance-limiting deconditioning if current exercise countermeasures were used on future spaceflight missions. These findings support the need for refinement of current countermeasures, adjunct interventions, or enhanced requirements for preflight physiologic and functional capacity for the protection of astronaut health and performance during exploration missions to the moon and beyond.

Aerobic exercise deconditioning and countermeasures during bed rest.

Bed rest is a well-accepted model for spaceflight in which the physiologic adaptations, particularly in the cardiovascular system, are studied and potential countermeasures can be tested. Bed rest without countermeasures results in reduced aerobic capacity and altered submaximal exercise responses. Aerobic endurance and factors which may impact prolonged exercise, however, have not been well studied. The initial loss of aerobic capacity is rapid, occurring in parallel with the loss of plasma volume. Thereafter, the reduction in maximal aerobic capacity proceeds more slowly and is influenced by central and peripheral adaptation. Exercise capacity can be maintained during bed rest and may be improved during recovery with appropriate countermeasures. Plasma volume restoration, resistive exercise, orthostatic stress, aerobic exercise, and aerobic exercise plus orthostatic stress all have been tested with varying levels of success. However, the optimal combination of elements-exercise modality, intensity, duration, muscle groups exercised and frequency of aerobic exercise, orthostatic stress, and supplementary resistive or anaerobic exercise training-has not been systematically evaluated. Currently, frequent (at least 3 days per week) bouts of intense exercise (interval-style and near maximal) with orthostatic stress appears to be the most efficacious method to protect aerobic capacity during bed rest. Further refinement of protocols and countermeasure hardware may be necessary to insure the success of countermeasures in the unique environment of space.

Lower limb position during treadmill jogging and fast running in microgravity.

INTRODUCTION: The second-generation ISS treadmill has a faster maximum operating speed than the current ISS treadmill. In normal gravity (1 G), bone loading benefits and cardiorespiratory stress are directly related to locomotion speed. A kinematic comparison of locomotion between 1 G and microgravity will provide information to evaluate the potential efficacy of fast running as an in-flight exercise countermeasure. METHODS: Subjects exercised on a treadmill at 3.13 m x s(-1) (8.5 min x mi(-1)) (JOG; N = 6) and 5.36 m x s(-1) (5 min x mi(-1)) (RUN; N = 5) in microgravity during parabolic flight and in 1 G. During microgravity trials, subjects performed locomotion using a subject loading system (in a configuration identical to ISS) with approximately 80% bodyweight loading. Kinematic analyses of joint position at heel strike were performed using video software. RESULTS: During the JOG trials, differences were found in thigh angle (microgravity = 54.09 degrees +/- 4.87; 1 G = 64.04 degrees +/- 3.12, mean +/- SD) and knee angle (microgravity = 33.17 degrees +/- 8.68; 1 G = 21.28 degrees +/- 5.22), indicating a more squatted position at heel strike in microgravity. No kinematic differences were found during the RUN condition. DISCUSSION: The subject loading system and decreased external load throughout the stride in microgravity may account for the observed kinematic differences during JOG. The kinematic compensations for microgravity during JOG may result in in-flight adaptations that are different from expected based on 1-G studies. However, similar kinematics between gravity conditions during RUN suggest in-flight training may provide benefits similar to 1 G.