A muscle contracts more strongly when lifting a 20-pound weight than when lifting a 5-pound weight. This is because more fibers are contracting, not because individual fibers contract harder.
a. true
b. false
a. true

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.