Each trainer takes into account your goals and develops a program geared towards reaching them. When building muscle is the objective, strategic periodization is necessary when developing your program. The goal is progressive overload – the most important law in strength training. Progressive overload simply means that your doing more overtime. For example, you could be adding more weight to the bar, doing more reps, and/ or having more productive training sessions.
Lower reps 1- 5 are effective for stimulating myofibrillar hypertrophy – is an increase in the number and size of the actin and myosin filaments within the muscle tissue. This is important because progressive overload is one of the primary necessities for continued long term growth.
Moderate reps 6-12 provides many of the benefit low rep training combined with the benefits high rep training allow by allowing for relatively heavy loads to be used whiling increasing time under tension. The increase time under tension will stimulate sarcoplasmic hypertrophy. Sarcoplasmic hypertrophy is an increase of the sarcoplasm and other non- contractile proteins within the muscle cells and is primarily induced by lifting light loads for higher reps.
Higher reps 15 or more is important due to its effect of muscle glycogen on protein synthesis.