- 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.