The principle of specificity states that one can target precise outcomes by selecting the energy systems used to fuel the exercise, the muscle group or motor pattern involved, and the mode or means by which the exercise will be performed. The principle of overload states that strength and endurance, flexibility, and range of motion increase only when muscle are made to perform greater-than-normal levels of work. The cancer exercise specialist manipulates overload by altering the frequency, intensity, and duration of exercise given the patient's particular situation, needs and desires, and physical status.