So we need to understand the different kinds of muscle fibres and how we can manipulate them.

First up, let's look at the difference types of muscle fibre and their contribution to muscular effort and how they utilise fuels. Every person is born with a unique genetic makeup and a predisposal towards a particular fibre type. Think of the different physiques of marathon runners, rowers and worlds strongest man competitors or weightlifters. Chances are each one has a higher percentage of a certain type of muscle fibre and that allows them to excel at their activity. Recruitment of muscle fibres can change due to stimulus, and specific training can increase fibre recruitment (myofibrilar hypertrophy) and even hyperplasia (fibre splitting, increase in number), so people do change their use of certain fibre types.

Slow twitch (Slow Oxidative), Type 1 muscle fibres are the smallest of the fibres. These are the muscle fibres we use to produce slow steady efforts such as long distance cardio or very light weights. These activities typically use a lot of oxygen and utilise fat as fuel. The mechanism for burning fat is much slower than the mechanisms for burning glucose and phosphates but the only waste products are heat and water and we can last much longer. Think of the physiques of Mo Farah, Paula Radcliffe or the finishing line of the marathon.
Larger muscle fibres are called fast twitch, Type 2 muscle fibres and there are two distinct types.

Type 2a (Fast Oxidative Glycolytic), are the next largest group of fibres. They produce faster efforts which may last 10 seconds to several minutes. They are used for activities such as 400m running, rowing, boxing, swimming. Efforts that are intense but not an all out sprint. They produce energy by burning a mixture of slow and fast release fuels (sugars and fats).
Type 2b (Fast Glycolytic) are the largest of the muscle fibres and produce high amounts of force very quickly but also fatigue the quickest. They are the fastest and most explosive muscles fibres and are used in heavy or explosive actions such as olympic weightlifting and sprinting. They rely heavily on the phosphagen energy system which breaks down very quickly.

Now it is important to understand that we may use a combination of these muscle fibres to perform a task but habitually the body will do things the easiest, the least energy costing way possible.

It does by way of order of neural recruitment. This is the brain activating groups of muscle fibres (motor units) based upon the work to be done. Consider this as a loose example.
I go to pick up my coat off the gym floor, the brain stores information and makes an assessment about the weight of the coat and assigns just enough force to lift the coat. I use my type 1 slow twitch muscle fibres and activate just enough motor units (groups of fibres) to lift the coat.

This time I go to move a large box of drinks off the gym floor, it weighs 20kg. I approach the box, my brain makes an assessment and activates Type 2a fast muscle fibres and Type 1 slow twitch to produce enough force.

Now I approach a deadlift. There is a barbell and it is loaded to, lets say, 80kg. My brain makes an assessment of the additional weight and activates Type 1, Type 2a and Type 2b muscle fibres. The biggest contribution will come from the Type 2b muscle fibres and the number and efficiency at which they perform will depend on my level of training.

A lifting rookie will probably not recruit enough motor units and may not yet have proper command of their fast twitch muscle fibres, type 2a or 2b. So they try to lift the weight with the type 1 fibres and it feels very heavy, they may struggle to lift or they may not make the lift at all.

An experienced deadlifter steps in front of the barbell and the brain activates the correct pattern of muscle fibres all the way up to 2b and he pulls the lift with ease.
Now! All muscle fibres will contribute to different actions and being stronger allows us to make use of more motor units, therefore a higher percentage of the muscle. More motor units working equals less work per motor unit. We will still only recruit the number of motor units necessary but by having that neural efficiency where the brain has the ability to recruit more motor units, movements begin to feel easier.

This means even if you are running, improving neural efficiency will make running easier as you will increase recruitment and have more 'backup', as such, than before.
Again, this is recruiting muscle fibres before the stage of growing them. Gaining weight would come down to energy balance, our food intake and specific lifting technique. Becoming stronger is not necessarily about lifting huge weights, or growing huge muscles it is about improving our neural adaptation from where we presently are.
Strength training is so powerful, both for weight loss and weight gain, and is vastly underestimated.

For weight loss, more motor units are being used, more muscle fibres are being activated - it feels easier to do more work. But energy cannot be created or destroyed, that additional work and effort has to come from somewhere and your nutrient turnover will go up massively as your body starts to turn over more and more fuel. This also goes on in between sessions. You take this new neural efficiency and strength and you will be applying it with whatever you do. More energy? Again that fuel is coming from somewhere. This is what we call NEAT, or Non Exercise Activity Thermogenesis - the cost of basic living and movement goes up.

For weight gain, more motor units are being stimulated we are getting blood into more parts of the muscle so we can grow more fibres. If you are hoping to grow, mix in some heavier low rep work with your high rep work to increase recruitment and see how you develop.

Now we understand the fibres themselves, we can look at how to use them in training.

Part two over the weekend where we look at different training outcomes. If you have any questions relating to this topic please feel free to drop me an email.

Have a great weekend.


Chris Adams