[Even if Jason couldn't see Aizawa--he would likely be able to hear the shrug in his voice.]

Except, your organs don't typically behave like muscles. The base comparison is generic enough to get the point across but it's more about moderating the amount of oxygen that gets set in your blood stream and how your heart pumps blood.

Gravity has an effect on that as well. Essentially speaking, it's theorized that gravity shifts could affect your equilibrium as well.

[And yet, Aizawa was trying to reassure Jason with this information.]