Can genetic traits be overwritten by muscle stimulation?

I look for the answer to whether muscle stimulation can change genetic traits, your congenital muscle fiber ratio, and how much performance change you can achieve with its help. The points described here are only meaningful if you understand the basics of muscle stimulation. If you don’t yet, read my series on the basics of muscle stimulation.

I will briefly summarize the essentials.

• With well-regulated electrical impulses, your muscles can be induced to contract.
• It does not matter to the muscle whether the impulse that triggers the contraction comes from your brain or from a device. In both cases the contraction happens in exactly the same way. And if the mechanism is identical, the training effect on the muscle is also the same.
• Which muscle quality the treatment affects—strength, mass, endurance, stamina, reaction speed, etc.—depends on the impulse parameters.
• However, you cannot improve all the listed muscle qualities at once. If you increase muscle mass, you lose endurance; conversely, if you work on improving endurance, you lose some muscle mass.
• With muscle stimulation you can bypass brain control, allowing you to isolate and focus on specific fiber types.
• Different impulses are required for the upper arm, chest, abdomen, back, or thigh (which is due to the different proportion of fiber types).
• Different impulses are required for slow, intermediate or very fast muscle fibers.

Can genetic traits be overwritten?

Your sporting results—i.e., what you are truly good at—are based on the muscle fiber ratio you were born with.

If type I (so-called slow) fibers dominate, you are suited to endurance sports. If you have many type IIb fibers, you can build significant muscle mass and generate huge force, but running 1 km will feel very unpleasant.

According to research, the genetically determined muscle fiber "mix" can only be modified to a limited extent. Type I fibers cannot be "converted" into very fast fibers and vice versa.

This means you are in a "genetic trap." If you have slow fibers, don’t try to become a bodybuilder, because you won’t be able to build huge mass.

If, however, you have IIb fibers, you may excel in strength sports and combat sports, but as a marathon runner you can only reach at best a mediocre result.

Scientific talent selection in sports, for example, aims to steer a child toward the sport for which their muscles make them best suited.

"Loophole": the intermediate (IIa) fiber

Current research suggests that the ratio of type I and IIb fibers is fixed and they do not convert into one another under any training.

It seems that type IIa (intermediate) fibers represent the only loophole.

Under appropriate training they tend to "change shape," i.e., optimize their capabilities toward type I or type IIb. (But not all of them and not completely).

The problem is that the activation of your muscles is under brain control. Voluntarily you are not able to tense only the IIa fibers.

No matter how you train, there is no natural way to do this.

But what is the obstacle?

Hennemann's size principle

During a movement, muscle activation follows the rule defined by Hennemann. According to this, muscle activation is under neural (brain) control and cannot be bypassed voluntarily.

• for a movement, the neuromotor system first activates the smaller, then the larger motor units
• first your type I (slow) fibers activate, then the IIa, and finally the IIb fibers
• IIa fibers begin to activate when the movement requires more than about 50% of your maximal force,
• the very strong IIb fibers only activate when the movement requires at least about 75% of your maximal force.

Consequences of the size principle

Most of your muscles are a mixture of white and red fibers, so there are no exclusively white or exclusively red muscles.

According to Hennemann’s rule, which fiber type your training targets depends on the training method.

If your goals are endurance-based, you perform low-to-moderate intensity, long-duration workouts. Such efforts require mainly type I fibers and to some extent IIa fibers.

Your endurance improves, your strength increases slightly, but your muscle mass grows only negligibly.

If your goals require sustained strength and power, you need to strengthen endurance and intermediate fibers, i.e., keep training load around 60–70% of maximal. This strengthens both type I and IIa fibers. Your strength increases, muscle mass increases moderately, and your stamina improves, meaning you can sustain high force outputs for longer (usually a few minutes). With such muscles you may excel at CrossFit, combat sports, canoe/kayak, etc., because these require near-maximal intensity to be tolerated for as long as possible.

If you want to increase muscle mass, however, you need a completely different training approach. You must train with weights above about 80% of your max, low repetitions, and very high force output. Such work activates not only type I and IIa but also IIb fibers. The latter provide the large mass. With such musculature you lose endurance. With that much muscle mass you are typically capable of maximal efforts for at most about 1 minute. Running competitions are not for bodybuilders.

"Bypassing method"

There is only one method that can "bypass" Hennemann’s rule: electrical muscle stimulation.

Type IIa fibers, according to Hennemann’s size principle, begin to activate when the required output uses more than 50% of your maximal force. The motoneurons supplying those fibers fire at frequencies between about 50–80 Hz.

By setting the appropriate frequency, pulse duration and intensity, you can very precisely focus stimulation on the IIa fibers and thus direct which way they shift.

With stimulation you can therefore "show" your muscles something you cannot achieve voluntarily in any way.

However, you must choose between improving endurance, sustained strength, maximal strength, or muscle mass. You can fully maximize only one of these. Increasing muscle mass will certainly worsen your endurance, whereas improving endurance will reduce muscle mass.

Read my article The theoretical basics of muscle stimulation as well.

Everything about sports muscle stimulators in one place