Muscle Fibre TypesMuscle Fibre Types

There are two kinds of muscle fibres

Slow-twitch: red/dark in colour Generate tension slowly Relax slowly Able to maintain a lower level of tension for a

long duration Useful during activities such as long-distance

swimming, cycling and running

Slow-twitch cont...Slow-twitch cont... Have low levels of an enzyme called myosin

ATPase – used to provide instant energy for muscle contraction

Also have low levels of glycotic enzymes which allow the release of glycogen within muscles

What is an enzyme? An enzyme is a protein that acts as a catalyst

for chemical reactions The enzyme itself is not affected by the

chemical reaction

Fast-Twitch Muscle FibresFast-Twitch Muscle Fibres

More pale in colour Tense and relax quickly Can generate large amounts of tension for short

periods of time High level of myosin ATPase and glycolytic

enzymes Activate 2-3x faster than slow-twitch fibres Short sprints, powerlifting, explosive jumping

The Importance of Myoglobin The differences between muscle fibre types =

the extent to which the muscle relies on oxygen in the production of energy

Myoglobin is a protein that delievers oxygen to working muscles

This allows energy-producing biochemical reactions to be sustained over a long period of time

Using aerobic processes for energy production = ability to sustain activity longer

Three Fibre Types 1 type for slow-twitch 2 types for fast-twitch Type I or Slow-Oxidative (SO): these muscles

generate energy slowly More fatigue-resistant Depend on aerobic processes

Type IIA Type IIA or Fast-Oxidative Glycolytic (FOG)

Intermediate High-speed energy release Glycolytic capacity

Type IIB Type IIB or Fast-Glycolytic (FG)

Store a lot of glycogen and high levels of enzymes necessary for quick contraction

Does not require oxygen

The Distribution of Muscle Fibre Types

A muscle's fibre makeup determines its function and at the same time what a muscle does gives us an indication of what it is made of

Use the terms tonic muscles and phasic muscles as a way to describe basic functions

Tonic Muscles

Assist the body with maintaining posture or stability during walking, standing, throwing, etc

High % of type I fibres (slow-twitch) i.e. Soleus – performs dorsiflexion and is key in

maintaining body posture

Phasic Muscles Higher % of type IIA and IIB fibres i.e. The biceps – key muscle for lifting and

power in the arm Lower % of type I

How Do I Find Out My Muscle Type?

The only way to find out what percentage of muscle fibre types are found in your muscles is to have a biopsy performed :( Must acquire a tissue

sample Take out a small

portion of the muscle and placing it under a microscope

Fibre Type and Athletic Performance

Read this section on page 93 of your textbook Answer the following questions: Give an example of a sport that requires fast-

twitch muscles fibres and an example of a sport that requires slow-twitch

How would an elite athlete maximize their performance?

What is the goal of the workout of an Olympic shotputter and a hockey player (think of the energy system they use)

Questions cont...

Endurance athletes train their muscles to? The goal of an endurance workout is to? What is the outcome of endurance workouts?