Short summary In order of importance: 1) Satellite cells must be activated, differentiated, and fuse with existing fibers, donating their nuclei. 2) Mechanical stress must be transmitted to the sarcolemma (mechanotransduction) and contractile protein structures within the sarcomeres. This will trigger focal adhesion kinases (FAK) that in turn initiate the downstream signaling events leading to an increase in the contractile and cytoskeletal protein expression/synthesis. 3) pH and oxidative stress must be acutely increased within the muscle fiber. Focusing just on the workout, this pretty much sums it up. If #1 doesn’t happen, you will not grow…ever. If number two doesn’t happen, you will grow a little, but you will soon reach the limits of the sarcoplasmic/nuclear ratio and growth will stop. If #3 doesn’t happen, you will still grow quite significantly, but the rate of growth might be enhanced or facilitated if #3 is achieved. #1 is achieved when a certain level of microtrauma is experienced by the fibers. This is brought about by load, eccentric contractions, and to a much lesser extent, hypoxia (A.K.A. #3) When load, eccentric contractions and #3 occur, each fiber will produce and release muscle specific-IGF-1 (sometimes called mechano-growth factor) The IGF-1 in turn seeps out of leaky sarcolemmas and acts on nescient satellite cells to initiate #1. Microtrauma is rapidly reduced from workout to workout (Repeated bout effect) thereby limiting the effectiveness of any given load to induce further hypertrophy. #2 is achieved by loading a muscle that is actively contracting. #3 is achieved by contracting a muscle (doing reps) until you create an oxygen deficit and subsequent hypoxic byproducts (e.g. lactate and oxygen radicals). The afore mentioned physiological principles of muscle growth are what we follow in order to ensure that 1,2 and 3 happen.