During exercise, energy demand in the muscles increases . which other body system directly provide for this demand

answer: 21

step-by-step explanation:

divide 630 by 30. 30 goes into 630 21 times

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.