Tracy suffered from chicken pox in her childhood. at the age of 25, she gets it again. however, this time she recovers with minimal treatment or

Antibodies in her system from her previous exposure.

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.