Hypertrophy, the increase in the size of a muscle, occurs in two ways: by adding proteins and by storing substances used for energy inside the muscle fibers. At the most basic level, hypertrophy is the result of more contractile and structural proteins being laid down inside a muscle. This occurs through progressive weight training; forcing a muscle to adapt to unaccustomed demands by growing bigger and stronger.
An unaccustomed demand is anything that your body hasn’t done before. If you have been lifting 10 pounds for an extended period of time, your body has no reason to add muscle or get stronger. It can already handle 10 pounds. If you suddenly start lifting 20 pounds, your body has to adapt by getting stronger. This is the fundamental principle behind strength training. Expose your body to something it hasn’t done before and force it to change by adding strength and muscle.
Growth can only occur by increasing the amount of weight you lift over time. No increase in weight lifted means no progress. You have to give your muscle a reason to grow. The addition of more contractile and structural proteins is called myofibrillar hypertrophy and it is mostly associated with lifting heavy weights and less reps. Rep ranges of 1-8 rely almost solely on this type of hypertrophy.
Greater muscle size is accomplished at ranges of 5-12, due to a combination of myofibrillar and sarcoplasmic hypertrophy. Sarcoplasmic hypertrophy is when the muscle needs to store more “stuff” inside the muscle cells to be used as energy. The muscles need more energy to perform the greater number of reps. Glycogen, enzyme and energy substrate accumulation lead to increased water storage. All of this “stuff”, combined with more contractile and structural proteins, increases the volume of the muscle cell and causes a bigger muscle.
When you lift weights within a rep range of 5-12 you get both types of hypertrophy. The more reps you do within the range, sarcoplasmic hypertrophy contributes to a greater degree. The fewer reps you do within that range, myofibrillar hypertrophy dominates. The important thing to understand, however, is that because sarcoplasmic hypertrophy involves storing nutrients inside the muscle, the resulting size does not result in strength. Only the addition of contractile proteins does that. This explains why someone with smaller muscles can be stronger than someone with bigger muscles.
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