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muscle activities |
co-contraction
| multi-joint contraction
Muscle Coordination
Muscle activities during motion
focal muscle
agonist or prime mover
agon = contest
the principal muscle that produces a joint motion or maintains a static posture
can be concentric,
isometric, or
eccentric
antagonist
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anti = against; agon = contest
the muscle that contracts in the opposite direction of the agonist
passively elongates or shortens to allow motion acted by agonist
synergist
syn = together; ergon = work
the muscle that contracts together with the agonist
stabilizer¡G
to stabilize the proximal component of the joint involved
neutralizer¡G to rule out unwanted motions
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postural muscle
anticipatory postural adjustment (APA)
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Co-contraction
agonists and
antagonists contract simultaneously
leading to joint approximation
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Actions of multi-joint muscles
single-joint muscle vs. multi-joint muscle
single-joint muscle¡G a muscle that cross one joint only,
e.g. the brachialis, the short head of the biceps brachii
two-joint muscle¡G a muscle that cross two joints,
e.g. the long-head of the biceps brachii, the grastrocnemius, etc.
multi-joint muscle¡G a muscle that cross more than one joint
e.g. the long finger flexors, the long finger extensors, etc.
active insufficiency
unable to reach the contraction force because of the limit of muscle length
examples¡G
Making a fist with the wrist extended is stronger than that with the wrist flexed
the strength of the elbow flexor decreases as the shoulder joint is more flexed
the contractile tension of the agonist is markedly weak when a
multi-joint muscle is attempt to contract at a shortened position,
i.e. the muscle contracts at the lower portion of its length-tension curve
passive insufficiency
unable to reach full range of motion because of the limit of muscle length
examples¡G
automatically open the hand as wrist flexed
difficult to reach the toes with the knee extended
as compared to that with the knee flexed
Even though the agonist may contract strongly,
motion may be limited because of the lack of excursion of the antagonist
NOTE¡G The totally insufficient grip strength produced with the wrist fully flexed is
due to the combination of active insufficiency of the long finger flexors and
passive insufficiency of the long finger extensors
- Have your friend keep his/her arm by the side and try to flex the elbow
to 90 degrees. Feel the maximum isometric strength he/she can generate.
Then, have his/her upper raise to the shoulder level and try to flex the elbow to
90 degrees.
Feel the maximum isometric strength again.
See which one is stronger.
Is this an example of active insufficiency or passive insufficiency?
Which one of the elbow flexor is responsible for this phenomenon?
- Consider the gastrocnemius that is a two-joint muscle at lower leg.
Please give an example that the gastronemius demonstrates
active insufficiency and another example that it presents passive insufficiency.
- Think the muscles you have already learned from the Anatomy class.
Which one is the single joint muscle? Which one is the two-joint muscle?
Multi-joint muscle?
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