Muscle types

There are three general categories of muscle within the body:

• Cardiac – (involuntary) forms the walls of the heart and pumps blood around the circulatory system
• Smooth (involuntary) – found in the walls of hollow structures e.g. blood vessels
• Skeletal (voluntary) – attached to bone

This article is concerned with muscle that we have conscious control over (voluntary) known as skeletal muscle. Skeletal muscle helps us create movement and support our skeletal structure. Having finite control over skeletal muscle will greatly enhance many aspects of our Wing Chun and our life.

Human skeletal muscles are made up of many bundles of muscle fibres separated by Myofascia, encapsulated by an outer fascia called the Epimyseum. Skeletal muscle is connected to bone by tendons and the beginning is at the Origin and the end is the Insertion. Through contraction (shortening) they create movement around joints. Muscles can only pull and as a result to have two opposing movements i.e. to flex or extend, there must be a muscle on each side of a joint, one to flex and one to extend. An example of this is the Biceps and Triceps in the upper arm, the Biceps flex and the Triceps extend the arm at the elbow joint.

Muscle Types

Muscle fibre can be categorised into two main types:

1. Slow twitch (Type I) muscle fibres
2. Fast twitch (Type II) muscle fibres. Fast twitch fibres can be further categorised into:
   • Type IIa fibres
   • Type IIb fibres

The above distinctions influence how muscles respond to training and physical activity, and each fibre type is unique in its ability to contract in a certain way. Each person has a predetermined mixture of both slow and fast twitch muscle fibres which is determined by genetics and, on average, we have about 50 percent slow twitch and 50 percent fast twitch fibres within the majority of skeletal muscle.

Slow Twitch (Type I / Slow Oxidative)

Slow twitch muscle fibres fire more slowly than fast twitch and are able to work longer before fatigue sets in. This is down the their ability to more effectively use oxygen from the blood to generate Adenosine Tri-Phosphate (ATP), the bodies fuel, enabling muscle contractions to continue over a long period of time.

An example of this is the way that you would use the muscles of the legs and postural muscles in the back to support your Yee Gee Kim Yueng Ma (basic stance) while completing Siu Nim Tao, the first form of Wing Chun.

Fast Twitch (Type II / Fast Glycolytic)

Fast twitch fibres are much better at generating short bursts of strength or speed and contract about twice as fast as slow muscles. They use anaerobic metabolism to create fuel and tire more quickly than their slower counterpart.

Fast twitch fibres in the Triceps and Biceps are essential for a Wing Chun practitioner in order to be able to quickly protract and retract the punch thus allowing the generation of great force using kinetic energy and the principles of energy production. The quick retraction, executed by the biceps, ensures that the spent punch is quickly returned to its ready position in preparation for its next movement.

Type IIa Fibres

Type IIa muscle fibres are also known as intermediate fast-twitch fibres and are able to use both aerobic (with oxygen) and anaerobic (without oxygen) metabolism almost equally to create energy. Also know as Fast Oxidative Glycolytic (FOG) fibres they are a combination of Type I and Type II muscle fibres.

Type IIb Fibres

Type IIb fibres generate ATP using anaerobic metabolism to create energy and has the highest rate of contraction of the muscle fibre types. This however comes at a cost and the result is that they have a much faster rate of fatigue and cannot operate for too long before needing rest.

What type do you have?

As noted the amount of each muscle type that an individual has is determined by genetics. This explains why some people excel in some activities and not in others.

It is not possible to change one type of muscle into another however it is possible to improve the abilities of each fibre with the use of specific training. In this way Type IIa muscles can be trained and adapted to get close to the ability of Type I or Type IIb fibres.

Aerobic activity for example will increase the number of mitochondria within a muscle cell resulting in a better ability to meet the demands for energy supply through the aerobic system.

Research is still looking at an ability of one type of fibre to switch to another type as some evidence exists to support this but to date the study is inconclusive.