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Muscle Action
Phrases that we need to know:
Antagonistic muscle action
Muscles are arranged in pairs either side of a joint. One generally flexes the
joint and the other generally extends it. (flexor/extensor)
The muscle that is contracting is the agonist/prime mover, while the muscle
that is relaxing is called the antagonist.
Concentric muscle action
A contraction in which the muscle length shortens is called a concentric
muscle action.
A concentric muscle action in which a constant load is lifted is called an
isotonic muscle action.
If a muscle contracts but is unable to lift the load (i.e. the muscle generates
tension but does not shorten), it is termed an isometric muscle action.
Eccentric muscle action
When force is generated by a muscle when the muscle is lengthening, it is
termed an eccentric muscle action.
For instance, the ‘upwards’ phase of a press-up is generated by the
concentric contraction of the triceps muscle in the upper arm. In the
’downwards’ phase, the smooth movement of lowering the body against the
pull of gravity is achieved by the eccentric action of the triceps i.e. the triceps
muscle group is exerting force to produce smooth movement, even though the
muscle is lengthening.
The muscle contracting eccentrically is acting as a ‘brake’ to help control the
movement of the body part during negative work.The eccentric action of the
quadriceps allows smooth flexion of the knee joint during the landing phases
of the ‘hop’ and ‘step’ in triple jump.
Isokinetic muscle action
These actions require maximal muscle contractions, which are carried out
over the full range of movement.
Such training is only possible with specialist equipment.