Muscles. The following letter will highlight key information on muscles, contractions and fibres, and will hopefully be informative.

3. Cardiac Muscles

Cardiac muscles are found in the heart, and are not under conscious control, either. They never die due to a rich oxygen supply.

Muscles contractions

Muscles function by contracting (they never . The origin of a muscle is always attached to a stationary bone, and acts as an anchor; the insertion inserts across a joint and attaches to a moving bone. For example, the origin of the bicep is found near the shoulder, and it inserts across the elbow to move the forearm.

There are two types of muscle contraction: isotonic and isometric.

Isotonic involves movement, so the distance between the origin and the insertion changes, i.e. lifting weights.

This can further be divided into:

Concentric – the insertion moves towards the origin and the muscle shortens under tension

Eccentric – the insertion moves away from the origin and the muscle lengthens under tension

Isometric has no movement, and so the distance between the origin and the insertion does not change, i.e. holding a weight in one position.

Agonistic muscle contraction

During movement, the muscle that contracts to cause movement is known as the agonist or prime mover, and the muscle that relaxes is called the antagonist. This is called an antagonistic contraction.

For example: as the hamstrings contract to cause flexion at the knee, the hamstrings are the agonist and the quadriceps is the antagonistic. This is reversed during extension: the hamstrings become the antagonist and the quadriceps the agonist.

The different muscles and their functions

There are a variety of different muscles in the body, each with their own use:

Pectorals – pull the arm across the chest

Abdominals – control flexion at the trunk

Deltoids – control abduction at the shoulder

Latissimus Dorsi – controls adduction at the shoulder

Trapezius – rotates the shoulders

Biceps – control flexion at the elbow

Triceps – control extension at the elbow

Gluteals – controls abduction at the hip

Hamstrings – controls flexion at the knee

Quadriceps – controls extension at the knee

Gastrocnemius – points the foot

Muscle Fibres

There are two different types of muscle fibres, fast twitch and slow twitch, and these have different properties:

Fast twitch – these are white, and provide rapid contraction. They tire easily, and are used in anaerobic activities, such as the shot put.

Slow twitch – these are red, and provide slow contraction, but they do not tire as easily as fast twitch fibres. They are used in aerobic activities, such as in long-distance running.

I hope that this letter has been informative, and will be of use to you.