Feature Weak muscles   Coming back to Earth, astronauts feel very heavy!     We rely on our muscles to walk, lift objects and climb stairs. However, in space muscles become weaker when there is no gravity to overcome. When astronauts come back to normal gravity on Earth, they suddenly feel very heavy and find it hard to keep their balance. Similar effects occur in elderly people and those who spend a long time in bed through illness.   Space studies give an opportunity to learn more about the effects of long-term muscle wasting.         Treadmills are used in space to prevent muscle weakness   Tests with astronauts have shown that several hours of daily exercise are needed to prevent muscle weakness. Among the machines used in space are treadmills for running on the spot and exercise bicycles. These are important for strengthening muscles and improving blood circulation.     Astronauts may also wear special trousers that pull blood to their legs and make the heart pump harder. These and other measures, such as drug treatment, have possible uses for patients on Earth.     One new machine being developed by ESA is the Flywheel Exercise Device. This includes a spinning wheel and can be used for exercise both in space and on Earth. It was launched to the International Space Station with ESA’s Columbus lab in February 2008 and is used as an advanced exercise device for astronauts. It will eventually be available for recovering patients and for training athletes.       Last update: 19 October 2011 - Living in space  •  A day in space (http://www.esa.int/esaKIDSen/SEMQ1JWJD1E_LifeinSpace_0.html)  •  Learning to live together (http://www.esa.int/esaKIDSen/SEM52JWJD1E_LifeinSpace_0.html)  •  Washing up (http://www.esa.int/esaKIDSen/SEMU7JWJD1E_LifeinSpace_0.html)  •  Meals for Martians (http://www.esa.int/esaKIDSen/SEMQ8F1DU8E_LifeinSpace_0.html)  •  Gravity and weightlessness (http://www.esa.int/esaKIDSen/SEMG2JWJD1E_LifeinSpace_0.html)  •  Weightless experiments help industries on Earth (http://www.esa.int/esaKIDSen/SEMYWUOZVAG_LifeinSpace_0.html)  •  Bed rest (http://www.esa.int/esaKIDSen/SEM9D6XDE2E_LifeinSpace_0.html)  •  Bone loss (http://www.esa.int/esaKIDSen/SEMSC6XDE2E_LifeinSpace_0.html)