“Systematic strength training produces structural and functional changes, or adaptations, in the body. The level of adaptation is evidenced by the size and strength of the muscles. The magnitude of these adaptations is directly proportional to the demands placed on the body by the volume (quantity), frequency, and intensity (load) of training, as well as the body’s capability to adapt to such demands. Training rationally adapts to the stress of increasing physical work. In other words, if the body is presented with a demand rationally greater than it is accustomed to and enough recovery time is given to trained physiological systems, it adapts to the stressor by becoming stronger….”
riseanddefyathletics.com 