So, when a lifter un-racks the barbell for a heavy set of 5 reps (think 80-85% of 1RM) the lifter is under the ideal conditions for optimally placing the most amount of muscle fibers under the optimal amount of mechanical tension. Heavy weights demand that the bigger type-II muscle fibers (those with the most potential for growth and force production) are recruited early in the set – and in this case, from the very first rep. We know this because even for the very first rep of a heavy set of 5 we have to exert maximal or near-maximal effort on the barbell in order to move it.
A similar event happens in a maximum effort set of 12 reps. Perhaps the first 6-7 reps of this set move with a sub-maximal amount of effort (submaximal implies less motor unit recruitment and thus less muscle mass being trained). But then, as fatigue starts to build in the working motor units, the barbell slows down, and the lifter must exert more and more effort to move the barbell for more reps. As the set progresses and voluntary effort increases, motor unit recruitment increases (specifically the bigger type II fibers), the barbell slows and a very high percentage of type II muscle fibers are placed under a high degree of mechanical tension. (Note: I am differentiating between a single 12RM set used here and the earlier example of metabolic stress that involved multiple sets of 8-12 on short rest periods. These are two fundamentally different events).
In essence, the last 5 reps of the 12RM, were similar to the 5RM in terms of the number of muscle fibers trained, even though there are still some qualitative differences between these two events. First, if we are concerned at all with force production, then the amount of weight on the barbell actually matters. Muscle fibers can experience a high level of mechanical tension even with relatively light loads, so long as those loads are pushed right up to the brink of failure. But this is not the same as the force production capacity of the entire muscle, much less the entirety of the musculo-skeletal system.
For force production, there is no end-run around heavy weight. And yes, it is possible to actually achieve some degree of hypertrophic response through the use of submaximal weights taken to failure, and achieve very little improvement in force production capacity at heavier weights (or even a loss of force production capacity).
So if we are primarily interested in hypertrophy, and we have a couple of potential pathways to get there, what do we choose? There are a few factors to consider. First, we already alluded to the fact that training with sets of 5 will automatically select for a load that gives you the dual benefit of placing a large number of muscle fibers under high degrees of mechanical tension and allows for actual strength/force production work to be performed (because the weight is actually heavy, not just perceived as heavy due to fatigue). If we compare to a set of 10 or 12 taken towards failure, we may potentially get the hypertrophy response, but we utterly lack the component that trains force production.
This has consequences in terms of long-term progressibility of a system that relies solely or mostly on high-repetition work. And progressibility must be accounted for. If there is no mechanism in the program that trains force production, then there is no mechanism that creates a catalyst for long-term progress. As odd as it may sound, your ability to squat 315 x 20, will by and large be predicated on your ability to squat 495 x 5 first. The best way to increase your capacity with submaximal loads is to increase your capacity with near-maximal loads.
Originally Posted by coldfire
