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The Effects of Zero Gravity & Exercise

By Bonnie Singleton ; Updated April 18, 2017

Ever since the first humans were launched into space in 1961, scientists have been studying the effects of weightlessness on human health. Longer missions began to uncover the fact there are some negative side effects from living and working in zero gravity, and it became vital to develop ways to combat these problems. Exercise is one of the primary ways to prevent health problems in space, just as it is on Earth.


Astronauts who live in space quickly become the victim of muscle weakness, bone loss and aerobic deconditioning due to the lack of gravity. The effects are similar to being bedridden for several months. To combat this problem, the crew on board the International Space Station must exercise for two or more hours every day using specially-designed machines that can work despite the lack of gravity.

Cardiovascular Impacts

Your body is accustomed to the pull of gravity on Earth to help maintain blood flow through your heart and blood vessels in your arms and legs. In zero gravity conditions, the blood rushes out of your extremities and pools in your torso and head. This leads to “puffy face syndrome,” with the veins in the neck and face standing out. Duane Graveline, MD, a former NASA astronaut and research scientist in aerospace medicine, points out that any reduction in the demands placed on your heart due to inactivity will lessen your heart's efficiency. In space, this can combine with a progressive loss of circulatory reflexes important in maintaining blood pressure, although exercising in zero gravity will help promote more normal blood flow and blood pressure.

Musculoskeletal Impacts

Even during periods of short duration in space, your muscles and bones begin to deteriorate. This is particularly true in your legs, which rapidly lose calcium in weightless conditions where they don't have much work to do. You’ll lose muscle mass, and your bones will become weaker. You might lose up to 10 percent of bone in your lower limbs, according to the Canadian Space Agency. It’s been estimated that astronauts risk losing two percent of their total bone mass for every month spent in zero gravity.

Prevention and Solution

A six-month study in the Journal of Applied Physiology in January 2009, measured the effectiveness of the astronauts’ exercise regimen at the time. The study found that, even though the crew members exercised, they lost an average of 15 percent muscle mass and 20 to 30 percent of muscle performance. Lead researcher Scott Trappe at Ball State University's Human Performance Laboratory likened this effect to aging when comparing a 20-year-old and an 80-year-old. At the time of the study, the average astronaut exercise regimen included five hours a week on a treadmill or exercise bike and several sessions with the interim resistive exercise device, or iRED, a machine designed to keep legs strong in zero gravity. Tappe and his colleagues concluded that astronauts need to intensify their workouts significantly and that more and harder weight training needed to be prescribed.

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