The overload principle is the physiologic mechanism that allows adaptation to stress. This concept can be applied in a variety of circumstances and may allow physical performance at greater levels. In an effort to improve athletic performance, many have adopted training methods that incorporate overload principles. These principles can also be applied in the patient population as it relates to physical rehabilitation. After injury, patients often present with progressive weakness and declining function. In an effort to return patients to their prior level of function, the overload principle may be applied. This entry reviews the basic principles, dosing theories, and application of the overload principle.