MUSCLE FIBER RECRUITMENT

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Conventional wisdom holds that different exercises should be applied to a muscle group from different angles for optimum development. Conventional wisdom, however, is notoriously unwise.

June 13, 2008

Written by the FLEX staff

The idea of exercises targeted to particular muscle groups from different angles is that each individual muscle must be hit with a movement so that it works directly and precisely, and the stress does not have to be shared (diluted) by other muscles in the group; i. e., a muscle group grows only from the sum of its parts, not from the synergism of its parts—so they say.

Certainly, this is not as valid as logic and common sense, both of which tell us that the more muscle fibers that you can activate simultaneously in a muscle group, the more it will grow. This is called muscle-fiber recruitment, and it's based on the fact that the human body acts in a systemic manner, performing work not by the sum of individual muscles acting in a disorganized manner, independent from their teammate-muscles in the muscle group, but by their collective power, each one helping all the others, synergistically.

The problem with using too many angles and isolation tricks is precisely what "angle-activists" claim as a benefit: namely, that you limit the stress of focus to only one region of a muscle group's fibers, to the exclusion of the rest of the fibers in that muscle group.

A good example is incline presses as a chest exercise. While it's true that both the upper chest (clavicular pectoralis) and lower chest (sternal pectoralis) portions of the pec share a common tendon of insertion, meaning that the fibers in both regions are activated whenever any part of the muscle complex is called into action, the angle nonetheless becomes the culprit by decreasing the range of motion for all of those muscles, thereby reducing stress on fibers throughout the muscle group.

Also, because of the isolation and angle, maximum strength cannot be applied, thereby reducing the maximum amount of stress that can be exerted on the overall chest body part. Essentially, the movement is a compromise exercise: half pecs and half shoulders, neither of which receives optimum stress to fully fatigue either muscle group. And that's only one example of limiting muscle-fiber recruitment; most workouts today are rife with angled exercises that over-isolate and under-recruit.

The only factor that fully recruits a muscle group's fibers is the heaviest weight that muscle group can resist in direct opposition to its contraction, and that means not at an angle.

The heavier the weight and the more directly it is applied, the more fibers are recruited to lift it, which means that the more fibers will be stimulated to grow larger (hypertrophy). It's simply a matter of force requirements over geometry.

That's not to say that only free weights should be used. When it comes to weight, a muscle cannot distinguish between a barbell, a machine or a suitcase full of rocks; its only concern is whether enough fibers are recruited to get the job done.FLEX.

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