Types Of Muscle Action


Muscles work in different ways. They can contract & shorten, contract & lengthen or contract & stay the same length, with no movement occurring. They can also relax & lengthen or stretch. To lift a weight for example, the muscles shorten. To lower a weight the muscles lengthen. To hold position, e.g pausing an activity the muscles stay the same length.

Here we are going to look at a number of terms used to distinguish between these different types of muscular activity

Isotonic – Describes muscle actions involving movement, i.e. concentric & eccentric

– Concentric: The muscle generates force & shortens. The origin & insertion move closer together; this is usually the lifting phase of body movement, e.g. the upward phase of a curl-up, press-up or squat.

– Eccentric: The muscle generates force & lengthens. The origin & insertion move apart, usually the lowering phase of a body movement, e.g. the downward phase of a curl-up, press-up or squat.

– Isometric: The muscle generates force and stays the same length, i.e. plank or wall sit.

– Isokinetic (Same Speed): The muscle actions involve movement at a constant speed, i.e. treadmill or bike.

– Stretching: The muscle lengthens and relaxes; the origin and insertion move further apart.

Roles Of Muscles

Efficient human movement is dependant on the coordinated activity of whole groups of muscles and will involve varying combinations of different muscle actions happening simultaneously. During any movement different muscles can be working in the following ways:

– Agonist/Prime Mover: The muscle(s) that contacts and causes a desired action, e.g. the bicep contracts during a bicep curl or the quadricep contracts during a leg extension.

– Antagonist: The opposing muscle(s) to the agonist that relaxes, e.g. the triceps during a bicep curl or the hamstring during a leg extension.

– Synergist: The muscle(s) that contracts to assist or modify the movement of the prime mover, e.g. during hip extension the hamstrings act as a synergists for the gluten Maximus.

– Fixators: The muscles that contact to stabilise the part of the body that remains fixed, e.g. shoulder girdle muscles stabilise the scapula to allow for efficient movement at the shoulder joint when the arm moves.



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