Human Biomechanical and Cardiopulmonary Responses to Partial Gravity – A Systematic Review

Abstract

The European Space Agency has recently announced to progress from low Earth orbit missions on the International Space Station to other mission scenarios such as exploration of the Moon or Mars. Therefore, the Moon is considered to be the next likely target for European human space explorations. Compared to microgravity (μg), only very little is known about the physiological effects of exposure to partial gravity (μg < partial gravity <1 g). However, previous research studies and experiences made during the Apollo missions comprise a valuable source of information that should be taken into account when planning human space explorations to reduced gravity environments. This systematic review summarizes the different effects of partial gravity (0.1–0.4 g) on the human musculoskeletal, cardiovascular and respiratory systems using data collected during the Apollo missions as well as outcomes from terrestrial models of reduced gravity with either 1 g or microgravity as a control. The evidence-based findings seek to facilitate decision making concerning the best medical and exercise support to maintain astronauts' health during future missions in partial gravity. The initial search generated 1,323 publication hits. Out of these 1,323 publications, 43 studies were included into the present analysis and relevant data were extracted. None of the 43 included studies investigated long-term effects. Studies investigating the immediate effects of partial gravity exposure reveal that cardiopulmonary parameters such as heart rate, oxygen consumption, metabolic rate, and cost of transport are reduced compared to 1 g, whereas stroke volume seems to increase with decreasing gravity levels. Biomechanical studies reveal that ground reaction forces, mechanical work, stance phase duration, stride frequency, duty factor and preferred walk-to-run transition speed are reduced compared to 1 g. Partial gravity exposure below 0.4 g seems to be insufficient to maintain musculoskeletal and cardiopulmonary properties in the long-term. To compensate for the anticipated lack of mechanical and metabolic stimuli some form of exercise countermeasure appears to be necessary in order to maintain reasonable astronauts' health, and thus ensure both sufficient work performance and mission safety.

Simulation of human gait with body weight support: benchmarking models and unloading strategies

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“…These devices use active control in order to render a constant force. Note that this is still different from actual simulated gravity because the load is applied only to the upper body (distributed via the harness), and not in a distributed way on each single body segment [14]. Accurate investigations for swing phase therefore generally require set-ups similar to a parabolic space flight [15,16], which are inconvenient to reproduce.…”

From Emotions to Mood Disorders: A Survey on Gait Analysis Methodology

“…In particular, after space mission, detrimental effects on the musculoskeletal system due to the loss of muscle mass and muscle strength may also affect mental health and recovery [123]. Partial/micro gravity exposure has immediate effects on gait characteristics that include reduction of GRFs, stance phase duration, stride frequency, stride length, and walkto-run transition speed [124]. After a long-term exploration in space, the astronauts who completed missions within two weeks still exhibited increased variability in ankle and knee joints [125].…”

Designing clinical trials for future space missions as a pathway to changing how clinical trials are conducted on Earth

“…The project started a few systematic reviews 1‐3 around specific questions in aerospace medicine that highlighted some issues around systematic reviews and primary studies in aerospace medicine. The methods to synthesize evidence on a focused health research question are well documented in the literature 4,5 .…”

“…The methods to synthesize evidence on a focused health research question are well documented in the literature 4,5 . However, there are specific challenges in reviews of aerospace medicine that we observed in previous reviews, 1,2 like databases and resources to search for studies (Table 1). The other issues are highlighted in Table 2.…”