Make sure you understand the following terms:
- plantar flexion
- dorsi flexion
|Flexion||Involves decreasing the angle between two bones, e.g. bending the elbow or leg|
|Extension||Increasing the angle between two bones, e.g. bending backwards at the trunk|
|Abduction||Moving body parts away from the body’s midline|
|Adduction||Moving bones towards the body’s midline|
|Pronation||Turning the hand to have it palm downwards (radius and ulna are crossed)|
|Supination||Palms facing upwards (radius and ulna are uncrossed and parallel)|
|Inversion||Moving the sole of the foot inwards at the ankle|
|Eversion||Moving the sole of the foot outwards at the ankle|
|Dorsiflexion||Pointing the toes upwards towards the tibia|
|Plantar flexion||Pointing the toes away from the tibia|
|Circumduction||Moving the end of a bone so that it makes a circle|
|Rotation||Moving the bone around a central axis|
Major Muscle Groups & the Microscopic Structure of Muscle
- provides an understanding of muscle action fibre types and their influence on activities
- Identifyies characteristics of fast and slow twitch muscle fibres.
- provides an understanding of the significance of fibre types on performance in different activities.
- provides an understanding of microscopic structure, sliding filament theory; agonist/antagonist relationship; joint actions (flexion/extension, etc.); contraction types (eccentric/concentric/isometric)
Summary of Muscles & Their Actions
There are three types of muscles in the body:
- smooth (intestinal wall and arteries)
Skeletal muscles are labelled according to the way the muscle fibres lie with respect to the tendon.
Fibres run in the same direction as the tendon. There aren’t a great number of these muscle types because they only produce low muscle force. However, they have great contractile range and so are found in muscles that require a great range of movement (e.g. gracilis muscle).
In these muscles, the fibres run at an angle to the tendon. They make up 75% of all the skeletal muscles in the body. They produce great force, but don’t have great range.
There are three types of penniform muscles:
- unipenate – branch to one side only (e.g. Semimembranosus)
- bipenate – branch both sides of the tendon (e.g. Rectus Femoris)
- multipenate – branch repeatedly (e.g. deltoid)
Muscle Fibre Types
There are two types of muscle fibres. Each has unique characteristics:
Fast twitch (white) fibres
These fibres are associated with explosive activities requiring speed and power.
They produce a great deal of force; however, they fatigue more rapidly than slow twitch.
View the video on sprinting, which depends on fast-twitch fibres.
Slow twitch (red) fibres
These fibres are smaller than their FT counterparts and are best suited to aerobic activities. They are associated with oxygen, hence the term “red” fibres. All muscles have a percentage of both types of fibres. This is genetically determined to a large extent.
For example, distance runners typically may have:
79% ST fibres
21% FT fibres
100 metre sprinters may have:
75% FT fibres
25% ST fibres
Muscle Fibre Types: Features
Characteristics of FT and ST fibres that you need to remember:
|Characteristic||Slow twitch fibres||Fast twitch fibres|
|Force of contraction||low||high|
Training – it is possible to improve the endurance potential of FT fibres (i.e. give FT fibres more aerobic tendencies). It is, however, hard to develop FT characteristics with people who have predominantly ST fibres.
Preferential treatment – the intensity of the task determines which muscle fibre type is preferentially recruited. If immediate and rapid response to a stimulus is required, then FT fibres will contract first, then ST fibres. However, ST fibres get preferential treatment if the task is of low intensity.