I made an arm brace because when you are in space for three years, you are going to need your arms for a lot of things like picking up large and small objects. Even running involves your arm. Also, because of microgravity, the bones begin to lose mass which makes people on mars more prone to breaking bones. Also, when you are on mars and your arm hurts, you will probably be focusing on the pain, and not on the mission. It is very likely that you injure your arm in three years, especially since 3 years on mars is 2,061 days which is more than how many days are on earth. That is why you should have an arm brace on mars.