What are High Threshold Motor Units?

Do you want to build size and make gains even during this quarantine? Do you want to get more powerful and gain strength so when it's time to get back in the gym or on the playing field, you’ll be ready to pick back up from where you left off and dominate the competition? Then, learning that it can be as simple as increasing movement acceleration and mental effort at the physiological level will lead to massive gains!

The simplicity of gains lies within the central nervous system (CNS) and the innervation of high threshold motor units (HTMU). They are the key to strength and size. Within larger nerve cells high threshold motor units innervate around 300-500+ muscle fibers, in comparison to low threshold motor units in a smaller nerve cell and only innervate around 10-180 muscle fibers. This means that in big muscles, high threshold motor units stimulate a greater amount of muscle fibers than in smaller muscles. This explains why Olympic sprinters have larger, more defined muscles than endurance runners.

According to the Henneman Size Principle, motor units and muscle fibers are recruited in order from smallest to largest, beginning always with slow-twitch muscle fibers. When a heavy load is used, slow twitch fibers will begin the contraction, but they will quickly be taken over by fast twitch muscle fibers. When load increases, the CNS will detect the greater weight or speed and recruit HTMUs.

In strength training and sports performance, movements will require different amounts of motor unit recruitment and  different types of muscle fiber recruitment. During movements with a lighter load you will recruit lower threshold motor units  because it is typically of lower intensity.  Conversely, if heavy strength movements or explosive ballistic movements are being performed, requiring high levels of force and power, higher threshold motor units and type II fibers will be recruited and utilized at a very rapid pace.

Checkout this podcast Dane did on High Theshold Motor Units!

Now how will this get me BIG??

In hypertrophy, HTMU recruitment is key! When light loads are lifted for very high reps (20+), or to failure, the CNS will recruit all available muscle fibers at the end of the set. For example, during the beginning of a set of high rep preacher curls, typically the body will utilize low threshold motor units but around rep 13 when fatigue starts to set in, the CNS will recruit HTMUs to meet the needs of the biceps brachii (a prime mover in the curl) to take over and complete the set for the fatigued fibers no longer producing enough force.

What about being more athletic??

HTMUs are the determining factor when trying to build explosive power. If you want to MOVE FAST, then you have to train with the intent to move FAST. When performing movements like jump squats, medicine ball throws, or short distance sprints (5-15 yards), the CNS will recruit nearly all the motor units in the prime moving muscles to maximize muscle fiber recruitment. Remember, as force and velocity increase so too will the HTMU recruitment.

Neural drive and mental intent will assist in HTMU recruitment. This is the combination of the “mind to muscle connection.” Through repetition the body becomes more experienced with movements, giving the brain and CNS a greater ability to contract HTMU’s at a faster rate and assist in accelerating a movement. When exhibiting intense focus and being locked in with performing a task, like blasting off the line during a 40 yard dash, you can increase your performance through mental intent. The brain will naturally learn how to activate motor units at a more consistent rate as the repetition of a movement continues. When the time comes to perform with perfect execution, the body will be able to coordinate appropriately at an accelerated rate.

Recap (what does this all mean??)

To get big and strong, it comes down to two very simple tips, have the intent to move fast and execute movement with complete mental focus. As the acceleration of movements increases, the role of HTMUs also increases to perform the movement, given they are responsible for high power and force production. The same goes for mental focus and neural drive. The more attentive you are while performing a task, the better the brain will be able to learn the movements, so when they are needed to be performed with max force, the CNS will key in on recruiting HTMUs at a much faster rate.

Utilize these tips in your training, and the gains will soon show for themselves!!