Core stability. The bodies anchorage to any exercise is related to the strength of the midsection. Weight training in itself will strengthen the core muscles. Most importantly, weight training will shock the muscles so they are put under different levels of stresses.

External stresses are variables such as torque tension, tempo, range of motion and recovery.  Muscle will adapt, so we need to keep them adapting. Applying these variables in a periodised fashion allows the muscles to always be challenged.