physiology

The Physiology of Muscle Contraction and Muscle Fibres for Athletes

All about that twitch!

When it comes to sports and exercise, we suddenly become very aware of our muscles, prioritising warm-up and cool-down exercises to ensure these muscles are taken care of. But, did you know that there are various muscle factors that can influence the type of exercise you perform?

There are three main types of exercises:

  • Endurance exercise is usually prolonged activity at a lower intensity. Beneficial metabolic adaptations for this exercise require an increased oxygen supply by the muscles.
  • Resistance exercise uses short, intense bursts of power output. Metabolic adaptations that suit are an increase in strength, power and muscle mass. This is the type of exercise that is typically used to ‘bulk up’.
  • Last, but not least, sporting activities usually consist of stop-start movements and utilise a combination of endurance and resistance metabolic adaptations.

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In order to perform these exercises, muscles have certain requirements, such as:

  • Sufficient energy
  • Oxygen
  • Appropriate nutrients

At the same time, metabolic waste and heat need to be removed and a person’s fluid and electrolyte balance must be maintained.

What is muscle contraction?

A muscle contraction is the ability of skeletal muscle, which is an excitable tissue that shortens in length, to move i.e. walk or run.

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What causes muscle contraction?

There are various factors that determine the ability of muscles to contract, and when it comes to athletes and sports, muscle fibre type can play a big part in this.

  1. The cross-sectional area of a muscle i.e. how big your muscle is
  2. Muscle fibre type
  3. Number of active motor units (cluster of muscle fibres)
  4. Motor neuron firing frequency (the stimuli of a contraction to occur)
  5. Muscle length
  6. Velocity (or speed) of contraction

It is this coordinated response that makes movement possible.

Does muscle fibre type affect sports performance?

Many people believe that muscle fibres may determine what sports athletes excel at and how they respond to fitness training. Understanding your muscle fibre types will help you determine which energy system and nutrients best fuel your muscles for your chosen activity, but if you wanted to know for sure what type of muscle fibres you possess, a muscle biopsy would be needed. An easier (and less invasive way) to know which muscle type you most likely have would be to identify the type of activity you excel at — are you a marathon runner? Or, perhaps, you're better at the 100-metre sprint.

Your skeletal muscle is made up of bundles of these individual muscle fibres which can be broken down into two types, namely slow-twitch muscle fibres and fast-twitch muscle fibres.

Slow-twitch muscle fibres

Slow-twitch muscle fibres have the following attributes:

  • Fatigue resistant
  • Rely heavily on the aerobic/oxidative energy system (meaning that they need oxygen in the process of generating energy)
  • Contain a lot of mitochondria, w