The age-old debate about the ideal rep scheme for stimulating muscle hypertrophy has yet to be resolved. Whereas some bodybuilders believe that you need higher reps to elicit the greatest gains, others have found that a somewhat smaller number works equally well.
The stimulus for muscle growth remains something of an enigma to scientists and laymen alike. Granted, some possibilities seem more likely than others, based on observations and available scientific data, but the exact cellular mechanism by which muscular force is converted into the alterations in contractile protein synthesis that lead to fiber growth is unknown. So it should come as no surprise that there's no agreement about the optimum rep range.
While I can't settle this debate, I can give you a better understanding of the repetition itself; in the hope that you can find the range that works best for you.
A Question of Load
How many reps should you perform? When you ask that question, you re really asking (or should be asking), How heavy should the weight be? In other words, assuming that you're training to muscular failure, the number of reps will dictate the maximum load per set, and vice versa.
If the answer to the question is a 10-repetition-maximum load, or 10RM, then you select a weight that enables you to perform 10 reps of the exercise in question before reaching muscular failure on the 11th attempt. If you're a neophyte lifter, you may be responding to this answer with another question: What is muscular failure?
Understanding Muscular Failure
Muscular failure is by definition a failure to generate the required force output. If you're performing 100-pound barbell curls, for instance, muscular failure will occur when, despite full motor unit recruitment and optimal firing rates, the force-generating capacity of your biceps falls below what's required to curl 100 pounds.
The load is your index of muscular failure; however, a load that will get you to failure more efficiently is not the most effective for building muscle.
If 100 pounds represents 90 percent of your 1RM on the barbell curl, then lifting this load until you hit muscular failure will only fatigue the muscle fibers very slightly. It's such a high percentage of your maximum that you won't get out many more reps beyond the first 90 percent-of-maximum effort. In other words, the force-generation capacity doesn't have to drop very far for the output to fall below what you need to continue the set. The evidence suggests, however, that performing more reps may fatigue the muscle fibers more. Obviously, this calls for a lighter load.
For instance, if you use 50 percent of your 1RM on barbell curls (50 pounds in the above example) and curl until you hit failure, you experience a greater level of fatigue, as the muscle fibers will be fatigued enough that the force output drops by a full 50 percent, a considerable amount.
This explains, in part, why lifting lighter loads to muscular failure produces a greater degree of discomfort and exhaustion, particularly in the case of compound movements such as the squat or deadlift. Because the working muscles are lifting a load that represents something far less than the maximum for this movement, the muscles accumulate a large quantity of metabolic by-products, such as lactic acid, before the number of contractile protein interactions falls below what it will take to continue the set. Since some of these byproducts are associated with the well-known "burning" sensation, the sensation is more pronounced when you lift lighter loads to failure. Extending the set, that is, reducing muscular force further by performing drop sets or forced reps, fatigues the muscle fibers even more, adding to the discomfort.
As discussed above, the debate over the ideal rep scheme for stimulating muscular growth is by no means settled. It's safe to say, however, that in all likelihood there's no one perfect number of repetitions; that is, no one perfect load.
Studies have shown that human muscle has a range of fiber types, and studies involving nuclear magnetic resonance imaging have suggested that there are metabolic differences among the different fibers in human muscle and among the muscles at distinct training levels.
For instance, as lactate accumulates during heavy resistance training, the pH may drop at a greater rate in type II fibers compared with type I. It's also important to note that there are differences in fatigue recovery times both between individuals and between muscle groups. In short, a one-size-stimulates-all repetition scheme is perhaps more fantasy than reality Nevertheless, you should understand what the physiological objective of training should be in order to find what works best for you.