Why do astronauts feel weak after returning to Earth?

<p style=";text-align:left;direction:ltr">Arabiaweather.com- <a href="http://jo.arabiaweather.com/content/%D8%B5%D9%88%D8%B1-%D8%B1%D8%A7%D8%A... face great difficulty acclimatizing when they return from their long journeys to Earth, not only because of the difference in gravity, but also because their red blood cell production decreases during their stay in space, which makes them feel weak on Earth.</p><p style=";text-align:left;direction:ltr"> The issue of decreased red blood cell production in astronauts after their return to Earth is documented by the US National Aeronautics and Space Administration ( <a href="http://jo.arabiaweather.com/content/%D9%86%D8%A7%D8%B3%D8%A7-%D9%83%D9%8... ), and it is known as &quot;space anemia&quot;.</p><p style=";text-align:left;direction:ltr"></p><p style=";text-align:left;direction:ltr"> But a Canadian test aboard the International Space Station hopes to discover the reasons for this decline, as the functions of red and white blood cells will be examined, as well as the levels of fats in the bone marrow of astronauts to see how they change during and after the space flight.</p><p style=";text-align:left;direction:ltr"></p><p style=";text-align:left;direction:ltr"> The test is expected to reveal how weightlessness (and the resulting lack of activity) affects the blood, and how those effects can be reversed, meaning how quickly an astronaut can return to normal.</p><p style=";text-align:left;direction:ltr"></p><p style=";text-align:left;direction:ltr"> On the ground, the accumulation of fats in the bone marrow and changes in the function of blood cells are associated with normal aging, and other conditions such as paralysis, osteoporosis, prolonged bed rest or limited movement, and therefore the results of this study may greatly benefit ordinary people who suffer from these diseases. cases even if they did not fly one day in Earth&#39;s orbit.</p>