The made up of glands found throughout the body that release
hormones into the bloodstream.

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.

It is called procrastination, doing something else to avoid a specific task.