Why astronauts spend two hours a day fighting their own bodies

Space · Published 8 October 2026 Swipe more like this →

In short: In microgravity, your body begins to dismantle itself. Without Earth's gravity to provide constant resistance, muscles wither and bones leach calcium at an alarming rate. To survive the journey to Mars or stay healthy on the ISS, astronauts must engage in rigorous daily workouts just to maintain basic human function.

The human body is evolutionarily hardwired for a 1G environment. In the weightless conditions of the International Space Station (ISS), muscles that are normally used for walking, running, or standing become redundant. This lack of use leads to rapid muscle atrophy and can even affect heart function, as the heart is primarily composed of muscle tissue. Simultaneously, bones begin to lose density almost immediately, increasing the risk of fractures and conditions similar to osteoporosis.

To counter these effects, NASA and other agencies have developed sophisticated exercise hardware. Early missions relied on simple elastic bands, but current protocols involve high-tech machines like the Advanced Resistive Exercise Device (ARED). To simulate conventional lifting within zero-gravity, ARED employs a flywheel and piston mechanism that delivers resistance; it debuted in 2008. The T2 treadmill plus the CEVIS (Cycle Ergometer with Vibration Isolation and Stabilization System) are vital instruments; these computerised units ensure exact loads for astronauts exercising two hours every day on average.

Despite these advancements, staying fit remains a significant hurdle for long-duration missions. A study using CEVIS data revealed that up to 17% of astronauts could still experience losses in muscle performance and cardiorespiratory fitness under current countermeasures. This highlights an urgent need for refined regimens. Research also shows that preflight training is vital; just as athletes train before a season, astronauts who undergo intensive strength conditioning before launch show improved performance while on the station.

The stakes are high for future exploration. A round-trip mission to Mars could take about three years, requiring astronauts to maintain health in both microgravity and the lower gravity of the Martian surface. Current research, such as ESA's ARED Kinematics study, is actively seeking the optimal workout prescriptions to ensure explorers don't arrive at their destination with fragile bones or weakened hearts.

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