CrossFit is: “constantly varied, high-intensity functional movement.” This is our prescription. Functional movements are universal motor recruitment patterns; they are performed in a wave of contraction from core to extremity; and they are compound movements–i.e., they are multi-joint. They are natural, effective, and efficient locomotors of body and external objects. But no aspect of functional movements is more important than their capacity to move large loads over long distances, and to do so quickly. Collectively, these three attributes (load, distance, and speed) uniquely qualify functional movements for the production of high power. Intensity is defined exactly as power, and intensity is the independent variable most commonly associated with maximizing the rate of return of favorable adaptation to exercise. Recognizing that the breadth and depth of a program’s stimulus will determine the breadth and depth of the adaptation it elicits, our prescription of functionality and intensity is constantly varied. We believe that preparation for random physical challenges–i.e., unknown and unknowable events–is at odds with fixed, predictable, and routine regimens.