Motor neuron recruitment, exercise and the whole picture

There is always lots of talk about the best way to get big or strong or even how not to put on too much size. Before we go into how it all works lets first break up the different areas.

You have three types of muscle fibres, type I, type II and type IIa. Type 1 is a slow twitch fibre that is responsible for more aerobic activities like running longer distances or light resistance work. They store triglycerides that they break down for energy. Triglyceride stores are created from fat, so these use fat as energy. Type IIa is more of a fast twitch fibre involved in sustained strength movements like a 400m race or lifting above 40% of your 1RPM. They have high glycogen stores that are created from glucose/sugar (not the kind from a chocolate bar). They can last for a good amount of time before running out of puff. Finally, type II fibres are explosive, think 100-metre sprint or a maximal lift. These have a very short shelf life when it comes to energy stores, working off of a system called the ATP system and only lasting about 10 seconds before running dry. When training you can fatigue one energy system and still have plenty to give with all the others and vice versa so when planning your programmes it is important to keep this in mind.

Next we look at motor units. When we lift any object or move in any way, our body has to decide on how much of our muscles to activate to appropriately complete the task. Your motor neurons are in charge of this. They control each motor unit that consists of some muscular fibres. Your bigger motor units with more growth and strength potential are only activated when you are lifting 60-100% of your 1RPM, in fact unless you are at 90-100% they won’t engage until you add speed to your lift. Only if you are putting everything you have behind the lift will these units start to recruit, if the lift is below 90%. Just so we are clear, when I talk about speed, I don’t mean you should be moving heavy weights at speed, but to move the weight as fast as you can in the correct form, if you are aiming at these bigger units. These are type II fast twitch moves and remember they only have around 10 seconds of bang before you’re out of energy.

This all fits together to show what can be achieved, for example, by well-conditioned athletes in the cross-fit games, being able to hit PB’s in big compound lifts even after some gruelling work outs before hand. This is due to the need of different energy systems and recruitment of different motor units for each event. Whatever result you want, strength or size, look at working through these systems to completely over load the muscle group, fatiguing the bigger units and then hitting the same area again with something for the smaller units running on a different energy system. This creates a more complete work out on the area and is great for quick size results. This will increase your time under tension and completely exhaust the area creating rapid change.




Christian Thomson

Body Transformation Coach & mentor at body core 

Find out how I use physiological and neurological techniques to create pain free powerful bodies