Sigmund freud had many critics and continues to be a controversial figure in psychology today. people today point out that he concentrated primarily on boys, did not study children, and based his theories on case studies rather than research.

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.