What might happen to the human heart during a trip to mars?
a. stop working completely
b. become too weak to pump blood
c. expand and become too large to work properly

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.