The CrossFit prescription is “constantly varied, high-intensity, functional movement.” Functional movements are universal motor recruitment patterns; they are performed in a wave of contraction from core to extremity; and they are compounded 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 then 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 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 for random physical challenges — i.e., unknown and unknowable events — is at odds with fixed, predictable, and routine regimens.