WHAT HAPPENS TO HEART RATE AND BLOOD PRESSURE IN SPACE?

As the force of gravity is reduced, there is a progressive shift of body fluid from the lower limbs to the upper body. This results in a decrease in the circulating blood volume as well as the number of red blood cells, thereby decreasing blood pressure. This change also decreases the amount the amount of blood that is pumped out during each heartbeat (cardiac output). Accordingly, although one might expect heart rate to decrease in space because there is no gravity, some studies have shown no change in heart rate. This could be explained by the decrease in cardiac output. Because there is both a decrease in the amount of circulating blood and there is a decrease in blood pressure, heart rate may remain the same in order to maintain a constant amount of blood being delivered to the tissues. There have been some studies, however, which have shown decreases in heart rate. See how Mark's heart rate responded to this environment.

WHAT HAPPENS TO MUSCLES IN SPACE?

Previous research has shown that although there is no muscle damage that occurs during space flight - predominantly because there is no gravity to load the muscles - as soon as the astronauts arrive back to earth they experience muscle pain and stiffness. This muscle pain is similar to that which we experience on earth after participating in any unaccustomed or strenuous exercise, and is caused by miniature tears to the muscle fibers. This pain usually occurs a little while after the exercise, and hence it has been referred to as delayed onset muscle soreness (DOMS). Other studies have shown that if an exercise causes this kind of response, it is likely that there may be some protective effect on that muscle and that if the same exercise is performed on a second occasion, the pain and muscle damage, may be slightly less.

Other studies have shown that significant muscle wasting (atrophy) occurs during long-term space flight, resulting in decrements in muscle strength. These changes are specific to the lower limbs seeing as one will tend to use their upper bodies for support while in space. Accordingly, Mark's exercise programme includes specific lower limb exercises that will aim to pre-strengthen these specific muscles that will limit the effect of weightlessness on his legs. These strengthening exercises will also help Mark to maintain his pre-flight muscle mass. This will be measured using the circumference of his thigh (mid-thigh girth).