Which of the following is a primary reason for the rapid growth of cancer? Cancer cells are disconnected from the body's control center; they receive no messages to stop growing.
Cancer cells can travel either through the bloodstream or the lymph system.
Cancer cells can invade, destroy, and replace other tissues.
Cancer cells can migrate throughout the body.

People who utilizes the progression principle will ensure their exercise program increases in frequency, intensity, time, and type. the changes need to happen gradually in order to ensure they make gains in their fitness program. a person who doesn't utilize the progression principle can still gain health benefits from exercising, but will not continue to improve in cardiovascular fitness.