In past issues of Applied Metabolics, I've pointed out that muscular size and strength can be mutually exclusive. That is, you can develop a substantial amount of muscle mass that isn't always accompanied by a gain in muscular strength. Until recently, the primary prescription for building larger muscles involved gradually making regular attempts to increase muscular strength. Specifically, this involved always making attempts to increase the amount of weight you used in any particular exercise. The notion here was that lifting heavier weights tended to activate the muscle fibers most prone to hypertrophy or growth, namely the type-2B fast-twitch muscle fibers. While the idea that activating these particular fibers does play a prominent role in muscular hypertrophy is true, it's also true that they are important for promoting increased muscular strength. A number of recent studies show that you can build as much muscle lifting lighter weights, equal to about 30% of one-rep maximum if you do higher repetitions in each set (25 to 30 reps) and train to complete muscular failure. Studies that have compared this style of training to lifting far heavier weights (90% of one-rep max) show that both styles of training produce equal results in terms of promoting muscular growth. A recent study found that training with weights equal to 20% of the one-rep maximum did not result in any gains while using weights equal to 40% of one-rep maximum produced a significant level of muscular size gains. The reason for this is that lifting lighter weights to failure activates more muscle fibers and also leads to a greater degree of metabolic stress within the muscle. Metabolic stress, in turn, activates anabolic growth factors in muscle so, in the end, you get similar results lifting light weights to failure as lifting heavier weights in conventional style, or not training to failure.
As I pointed out in an article in the February issue of Applied Metabolics, some sports scientists theorize that the light and heavy training styles tend to work more specific muscle fibers. That is, training light to failure will tend to activate mostly the type-1 or slow-twitch muscle fibers. These were formerly thought to be not capable of much muscular hypertrophy compared to the type-2 fast-twitch muscle fibers because the latter fibers have a larger motor neuron connection and therefore are capable of exerting more force and strength. That, in turn, would result in a greater potential for increased muscular mass. However, it's now known that type-1 fibers are capable of much more growth than was previously believed. And that is why the high rep, training to failure type of training can result in muscular growth. But what is often not discussed is that while the high rep, light weight style of training can produce comparable degrees of muscular growth compared to lifting heavy weights . . .