LIFT LIGHT OR GO HEAVY?
'Go heavy or go home' is the mantra heard across gyms worldwide. But, there are two critical avenues of muscle growth: myofibrillar hypertrophy and sarcoplasmic hypertrophy. Myofibrillar hypertrophy is the growth of actual muscle fibers, which is mainly induced by lifting heavy generally 70-85 percent of your one-rep max. Sarcoplasmic hypertrophy which occurs with high reps is the increase of the content of muscle cells responsible for converting glycogen to ATP.
ATP is something you want whatever your goal. It's the body's 'energy currency' for muscle contraction, protein synthesis (construction of muscle fibers) and a host of numerous metabolic processes. Thus with a lack of the ATP build-up (that comes with sarcoplasmic hypertrophy) required to support protein synthesis, the trainee hits a plateau with muscle growth. The muscle fibers don't have enough of what they need to grow.
It is worth noting that although the phases of hypertrophy are separated for general instruction purposes, there is an overlap between both. Even during the high repetition phase— a cornerstone of sarcoplasmic hypertrophy—the trainee will still experience some myofibrillar hypertrophy. Going heavy shouldn't always be your go-to move. You need both.