Science and Art Of Exercise
Human beings have the same basic physiology. Fundamental components and principles of fitness apply to everyone's training. Each individual does, however, have a unique combination of genetics, physical history, exercise experience, preferences, goals, etc. In working with the training principles, he/she learns the art of making those principles work best for his/her own fitness and health.
Specificity - The type of exercise demand (or stress) placed on the body dictates the type of adaptation that will occur.
Overload - A greater than normal stress or load on the body is required for training adaptations to take place. The variables can be intensity, duration, or frequency of an exercise(s).
Progression - To produce performance gains and other higher results, overload must become progressively greater. In the absence of such progression, the body receives no stimuli to which to adapt.