The heart has __one way valves which open and close with each heartbeat. A. one
B. two
C. three
D. four

A. hannah wants to improve her cardiorespiratory fitness levels, so she begins to alternate running on a flat track with running up stadium stairs. this principle is known as a type b tedium c time d frequency 2. charlie is easily winded during soccer practice and wants to improve his cardiorespiratory fitness. which activity would be best for him to choose? a lifting weights b walking from one class to another c running in a 5k race d riding a bike at a leisurely pace 3. felicia just began running this past month, but since she continues to run the exact same route and exact same distance every day, she is growing bored with her runs. this principle is known as a tedium b progression c specificity d reversibility