Exercise must be done a minimum of three days per week, but five is better and most experts recommend six. However, the frequency depends on the fitness component being targeted. Where five to six days per week is recommended for cardiovascular fitness, exercises targeted toward improving muscular fitness should only be done every other day.

Intensity refers to how hard you exercise. The intensity of your exercise should always place more demand on your body than usual, therefore requiring more effort. There is a critical balance that must be in place, since too much increase in intensity can result in injury, while not enough will result in little or no improvement. The decision of how hard to exercise depends on two things: your present level of fitness AND the fitness component being targeted.

Time refers to how long or how many minutes you exercise. An effective exercise bout must be maintained for a certain length of time, depending on the component of fitness. For example, to increase cardiovascular fitness, exercises like jogging, biking, and aerobics should be done for 15 to 30 minutes.

Principle of Overload
Various systems of the body will become stronger if the demands that are placed on it (overload) are increased. Although for improvement to occur overload is necessary, the overload should not be so excessive as to put undue stress on the body and risk injuries. The body must be given adequate time to adjust to the new demands. The principle of overload is illustrated in the legend of Milo of Crotona, a famous athlete whose strength increased by lifting a small calf several times a week. The calf, of course, got heavier as he grew and Milo's muscles became stronger. The application of the principle of progression made Milo of Crotona legendary because he was the only person in his village that could lift a full size bull. Remember that a calf takes time to grow into a full size bull, as does your body to adapt to new demands.

FIT Principle
In order to increase overload, at least one of three variables must be increased; Frequency, Intensity and/or Time. Frequency refers to how often exercise is done. Exercise must be done regularly to reach and maintain a desired level of fitness. An exercise program should spread activity out so that something is being done daily. But in today's society people seem not to have time for exercise.

Principle of Progression
Progression is gradually doing more than your body is used to doing. Remember Milo of Crotona. Your body must be given time to adapt as you work harder. A progressive increase in overload is essential to give your body time to become accustomed to its new workload. Progression equals safe improvement void of injuries.

Principle of Specificity
Simply put, the principle of specificity means that specific exercises must be done to improve specific components of fitness in specific body parts. Stretching must be done to increase flexibility, but will do nothing for cardiovascular fitness. If you want to increase muscular fitness in you biceps, squats will do you no good.



Summary
There are three basic principles of training (overload, progression, and specificity) that must be applied in an exercise program. Overload can be achieved by increasing one or more of the variables; frequency (how often), intensity (how hard you work), or time (how long you work). Your body adapts to added workloads, but only if placed on it gradually or progressively. In order to improve specific components of fitness in specific body parts, appropriate exercises or exercises that are specific to that fitness component must be done.