I have received quite a few requests on addressing the topic of muscle activation. In my post about targeting the Glutes and Hamstrings and in my “Tighten the Lower Body” Series I already pointed out that a specific Warm up Routine is necessary to activate the Glutes. However, some people seem to feel the Glute Bridge, which is normally a Glute Isolation exercise, mostly in their Quadriceps (front of the thighs).
The reason for this lies in the neuronal connections between the brain and the muscles. If you haven’t utilized a specific muscle much before, your brain will not be able to activate all muscle fibers at once. If you think about it, it makes sense. The body tries to consume the least energy as possible, so why should your brain activate all parts of a muscle if it is not used anyway?
To effectively activate the muscles we want to train during the workout, I want you to have a general understanding of how the brain and the muscles are connected to each other. In my experience, what I learned in med school has helped me a lot in understanding how to train my body to overcome my muscle imbalances due to scoliosis.
Scientific Background: Motor pathways
This picture illustrates the connection of your brain and muscles in a very simple way. There are different parts of the cortex of the brain that are responsible for the execution of different things: Movement, seeing, hearing, emotions etc. On this picture you see the motor cortex, which is again divided into regions that look after different body parts. In those regions there are millions of neurons. They are connected to the motor neurons in the spinal cord via the pyramidal and the extrapyramidal system (colored green and red). These motor pathways are stimulated via activation of different parts of the cortex and/or thalamus. The thalamus is a station in the brain that basically either tells the cortex to stop stimulation of the motor pathways or to activate them.
The motor neurons are connected to our muscles via nerves and their activation determines the number of muscle fibers that are stimulated. One motor neuron often activates many muscle fibers at once. This is called a motor unit .
In our muscles we have little receptors that detect whether the muscle is contracted or stretched and this information is sent to the motor neurons in the spinal cord. When one muscle is contracted, the antagonist to that muscle is stretched and vise versa. This is how we are able to contract the Quadriceps (front of the thighs) and stretch the hamstrings (back of the thighs) to raise our knees, for example.
Back to the motor unit: There are smaller and bigger units, as there are smaller and bigger motor neurons. The muscles in our eyes, for example, contain of 100 – 300 muscle fibers. In contrast, the big leg muscles are innervated by big motor neurons as part of a bigger motor unit. They consist of 2000 muscle fibers!
Now, the next question is: How do we activate 2000 muscle fibers?
When a muscle is activated, smaller motor units are recruited primary. As the demand increases (for example when you lift something heavy), more and more muscle fibers need to be stimulated to be able to execute the movement. (Hennemansches Principle). To be able to maximally contract a muscle, the neuronal impulse to the motor neurons needs to be increased to its full potential.
Now that we know how movement occurs, we can conclude that to really activate all muscle fibers of a motor unit we need to do one thing: Lift heavy.
So, should we just jump straight into heavy sets of Squats? No. The information above tells us that a muscle simply needs a lot of impulse to be activated. This is where the principle of Pre – Exhaustion plays an important role.
Pre – Exhaustion
Body builders are really good at activating all their muscle fibers. They often do a few sets of light weight exercises before they hit the heavy weights to exhaust the muscle just a little bit – as much as is needed to fully stimulate all muscle fibers when lifting heavy.
Now, it is not my goal to become a body builder. I train because my muscles help me to straighten out my spine and pelvis and make it possible to move without being in pain. You might have different goals, like shaping your body, increasing your metabolism, weight loss or just living a healthy life.
But, in order to achieve our goals, we basically need to train like a body builder (not eat like one though) and do light isolation exercises before we hit the heavy weights. Whatever muscle group you want to train that day, there are specific isolation exercises that really fire up solely that muscle. At first, you will not reach 100% activation, but as you repeat the stimulus over and over again, your brain will notice that a bigger impulse is needed.
Then you will be able to fully engage the muscle and for example feel Squats mainly in your Glutes and not your Thighs. I am proud that I reached that point after a half a year of Isolation exercises! Now, remember that your body might respond differently and be much faster or slowly.
To sum it up:
It all comes down to this: If you want to work out, you need to focus on what you are doing and really try to squeeze the muscles you are working as much as possible. It will be hard at first, because your motor pathways are not accustomed to that increased stimulus, but our bodies adapt quickly. After some time, you will be amazed how strong your body actually is!
Also, I find that trying to focus solely on the muscle I am trying to build is like a meditation. I cannot think about what I experienced in the hospital that day because otherwise I might lose my form and injure myself. And really, working out alone is pretty tough, so why should you waste your time?
In the next posts I will share exercises that focus solely on these muscles. In my experience, these are the muscles that are the hardest to activate.
- Lower Body : Glutes, Hamstrings – only
- Upper Back
- Latissimus dorsi (creates the Illusion of a smaller waist!!)
I hope this post created a general understanding of how movement works and how we can use that knowledge to shape our bodies!
Which muscles do you find the hardest to activate? If there are other muscles you would like me to add, speak up now 😉
References: “Physiologie des Menschen (Human Physiology)” – Schmidt, Lang, Heckmann – 31. edition0