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Muscle Fiber Types

What are the Different Muscle Fiber Types

Red Slow Twitch Muscle Fibers:

Slow Oxidative Type 1 Twitch muscle fibres contract efficiently in the presence of oxygen during aerobically based activities. Oxidative fibres have a high myoglobin content, which not only helps support their oxygen dependency, but also imparts a red colour to them, just as oxygenated haemoglobin is responsible for the red colour of arterial blood.

Accordingly, these muscle fibres are referred to as red fibres. Slow Twitch muscle fibres have the ability to use fat as a fuel source, but only during aerobic conditions. Fat cannot be mobilised for energy without the presence of oxygen and carbohydrate.

Intermediate Muscle Fibres:

Intermediate Slow Oxidative Type 2a Twitch muscle fibres share characteristics of both other fibre types. They can adapt to use A.T.P. like the fast twitch fibres, as well as having a high oxidative capacity like the Slow Twitch fibres. They contract more rapidly than the Slow Twitch fibres and can maintain the contraction for longer periods of time than the Fast Twitch muscle fibres. In humans, most of the muscles contain a mixture of all three types. The percentage of these various fibres not only differs between muscles within an individual, but also varies considerably among individuals. You cannot increase the total amount of muscle fibres, but you can increase the proportion of existing muscle fibres by manipulating training so that the intermediate muscle fibres adapt, and increase the proportion of either Fast or Slow Twitch muscle fibres, which takes up to three weeks.

White Fast Twitch Muscle Fibres:

Fast Glycolitic Type 2b twitch muscle fibres are used during short bursts of energy and physical activities that are predominantly anaerobic in nature, e.g. fast sprints. They contain an abundance of glycogen for energy. These glycolitic fibres contain very little myoglobin and therefore are pale in colour, so they are sometimes called white fibres. Fast twitch muscle fibres use primarily the A.T.P - pcr and Lactic Acid energy systems. Therefore, the amount of each type of muscle fibre you possess may have important implications for weight training and certain sports. Although not everyone has the potential to perform at elite level, it is still possible to maximise the capacity of each of the three energy systems by adopting specific training strategies.

People with a higher percentage of white fast twitch muscle fibres will automatically be good candidates for achieving results in strength, bodybuilding and power training strategies, whilst those with a greater proportion of red slow twitch muscle fibres are more likely to gain optimum results in endurance based activities.

Training Gains:

During any 4 to 6 or 8 to 12 week meso cycle, regardless of whether you are training for bodybuilding, endurance, strength training, cardiovascular fitness, or fat burning, you must always use exactly the same exercises during the entire meso cycle so that you ensure maximum muscle fibre recruitment and that the body can learn the most effective way in which to perform these exercises, the most efficient way of processing nutrients and removing waste products, and also the best way of maintaining and recovering from the demands imposed.

Apart from the type and length of training, nutrition and rest days, gym or endurance, gains will be highly dependent on the percentages of the relevant muscle fibre types that the trainer possess.

After the first few weeks of training gains will be further increased as a result of the intermediate fibres adapting to the type of overload / training performed, thus becoming more efficient. As they do so they either convert to fast or slow twitch muscle fibres. This is why (allowing for all other factors that affect achieving gains, such as the type and length of training, nutrition and rest days) after the first 4 to 6 weeks, people with a large proportion of intermediate muscle fibres make surprisingly fast gains either in terms of endurance or muscular gains.

The reason for this 4 to 6 week time scale is due to the fact that the first two weeks of a new training cycle is where the muscle fibres are learning to recruit the existing muscle fibers in the best sequential order before you can get the optimum performance from those muscles. It will then take a minimum of another two weeks for the body to learn to recruit the pink intermediate muscle fibers. The new maximum output of that new exercise is therefore going to be 4 to 6 weeks.

The adaptation period will shorten for advanced trainers due their experience of training which conditions the muscles and energy pathways to recruit muscle fibres more effectively than trainers who have just started out. The exact length of the shortened time scale cannot be given as this will be totally dependent on the type of training and the genetics of the individual in question.

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