On Earth and in space

When they are used less, our muscles end up deconditioned. To better support cosmonauts subjected to this phenomenon after a long stay in space, specialists are proposing innovative study protocols.

Walking, running, jumping, but also simply sitting or standing, in normal circumstances our muscles are called upon all day long. " The simple fact of resisting the Earth's gravity involves mobilizing our muscular system," explains Angèle Chopard, researcher at the Dynamics of Muscle and Metabolism laboratory.¹. But what happens to cosmonauts who are subjected to the microgravity environment? " Their muscles, especially their postural muscles, are drastically less solicited, and this form of inactivity leads to general deconditioning, particularly of the musculoskeletal system, which translates at muscular level mainly into loss of strength, atrophy of muscle cells and increased fatigability", answers the researcher.

To better study this phenomenon, Angèle Chopard and her colleagues Guillaume Py and Thomas Brioche have access to microgravity simulation experiments on the ground, using two protocols developed by space agencies, designed to reproduce on Earth the microgravity conditions faced by cosmonauts. The first involves prolonged bed rest, with a 6-degree head-down slope, "to mimic the increase in fluid return to the head in microgravity", explains the specialist. For the second protocol, called "dry immersion", volunteers are immersed in a water bath from which they are totally isolated by plastic sheeting. "This floating model results in faster deconditioning, on the order of three times faster than in simple bed rest.

While their guinea pigs take it easy, the researchers subject them to biological tests and samples designed to measure their body's response. " For us, the aim of these studies is to determine how best to prevent muscular deconditioning, not only for cosmonauts but also for patients who have to undergo prolonged clinical bed rest, for those who have had a joint immobilized, or for those who are chronically inactive," explains Angèle Chopard.

In terms of prevention, the most effective measure is still physical activity. "It's the best countermeasure against muscular deconditioning, but it must be adapted to spatial conditions and combined with nutritional supplements, for example.

photos © ESA/NASA, CNES/Emmanuel Grimault, Rachel Barranco

1. DMEM (UM, Inrae)
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