The Law of Muscle Fiber Recruitment

As far as building muscular mass is concerned, the sole objective is muscle fiber recruitment. The more muscle fibers recruited, the more activated; the more activated, the greater the growth stimulation. It therefore stands to reason that the more muscle fibers called into play or made to contract against resistance, the more muscle fibers will be stimulated to hypertrophy, or grow larger. In this post we would like to talk about how the muscle fiber recruitment process works. Also, we will show you the ways how to achieve maximal muscle fiber recruitment so that you can increase the size of your muscles in no time.

How the muscle fiber recruitment process works?

When your body needs to move or perform a certain task, it calls upon your muscles to complete it. We have two types of muscle fibers to do this:

• Type 1 – Slow Twitch fibers are slow contracting, lower force producing, suitable for long-lasting activities, and have lower fatigability;
• Type 2 – Fast Twitch Fibers are fast contracting, high force producing, not suitable for endurance (they quickly run of power), and have high fatigability (low resistance to fatigue);

It was demonstrated clinically in 1973 that, at light loads, slow-twitch fibers contract and are capable of sus­taining repeated contractions at this relatively low inten­sity. Since these fibers are weaker, they’re not suited to a higher intensity of effort or overload.

If a greater load is imposed upon the muscle, a progressive recruitment of larger and stronger (fast-twitch) muscle fibers occurs. Thus, when the load increases from light to heavy, there is a progressive increase in the number of muscle fibers involved in the contraction.

Something we find exceptionally interesting is that our body always calls the slow twitch muscle fibers before the fast twitch. It does not matter what kind of task is being performed. If you’re walking through the woods and see a bear, as soon as you start running for your life, your body is going to recruit the Type 1 fibers first. Even if it’s only a nanosecond before the fast twitch fibers will also start to act. Think of a car shifting from first gear to second or a thermometer rising. The Type 1 Slow twitch fibers engage first. Then, if the load becomes too great, or the demand too high, the Type 2 Fast Twitch fibers take over. We hope this helps clarify the muscle recruitment process.

So, what’s the bottom line?

The nervous system will only switch on as much muscles as it needs to overcome the resistance.

In essence, light loads, regardless of how many sets and reps you perform with them, recruit primarily slow-twitch muscle fibers, which have the lowest capacity to increase in size. Heavier loads recruit fast-twitch fibers in addition to the slow-twitch fibers already activated.

From this we can conclude, quite without fear of contradiction, that the amount of weight lifted, as opposed to the speed of the contraction, is what recruits and stimulates the greatest amount of muscle fibers, thereby allowing for the greatest increases in size (muscle hypertrophy) and strength.

Closing thoughts about the muscle fiber recruitment

According to the law of muscle fiber recruitment, the heavier the weight, the more muscle fibers are called into play to move it. Conversely, the lighter the weight, the fewer fibers that are required to move it.

As a result, you must consistently strive to lift heav­ier and heavier weights instead of increasing the number sets and repetitions. Consistent increases in size and strength are your goals, after all.

If you have the fiber recruitment potential to bench-press 200 pounds for 6 sets of 30 rep­etitions, yet the most you ever lift in any given workout is 125 pounds for 6 sets of 30 repetitions, then neither your muscle mass nor your strength will ever increase. They don’t have to: the muscles are only being called upon to do work that’s well below their existing maxi­mum capacity. And that work, incidentally, is quite capable of being handled solely by the slow-twitch fibers, which happen to be the ones that have the least growth potential.

The law of muscle fiber recruitment makes it abundantly clear that you must use a load of at least a threshold poundage, since in the body’s ongoing effort to conserve energy, it activates only the minimum number of muscle fibers required to perform a particular movement for any given demand.