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Dear colleagues:
About two weeks ago, I posted a message regarding the definition of
'antagonist'. I am grateful to all the individuals who spent their precious
time to respond to my message.
First, here is the original message:
---------------------------------------------------------------
According to the textbook I am using for my undergraduate Kinesiology
course, 'antagnist' is defined as "the role played by a muscle generating
torque opposing that generated by the agonists at a joint". Then it goes,
"When a muscle opposes a movement at a joint through development of
eccentric tension, it is acting as an antagonist." I witnessed similar
statements in some other textbooks I happened to possess. But I believe
there is a discrepancy between these two statements.
The definition implies that the antagonists opposes the agonists for fine
control of the movement and safety. When the agonists produces too much
tension or when the joint angle reaches the extreme of the joint range of
motion, the antagonists will produce tensions to control or slow down the
joint motion for fine control and safety since muscles produce tension only.
When the agonists contract concentrically, it is obvious that the
antagonists should contract eccentrically to slow down the joint motion. So
both statements above seem to agree. But what about the eccentric
contraction of muscles due to external load such as gravity?
Let's imagine some one is doing pushups. The triceps contract concentrically
during the up-phase, but eccentrically during the down-phase. According to
the second statement above, the triceps are the agonists during the
up-phase, but the antagonists during the down-phase. Which group of muscles
are the agonists in the down-phase then? Since the elbow flexion during the
down-phase is basically caused by the gravity, the elbow flexors can not be
the agonists. So the definition does not hold here.
Here is my view:
We can view the triceps as the agonists in both phases? The main job of
the muscles which the man intended during the down-phase was to slow down
the elbow flexion against the torque produced by gravity. Triceps are
undertaking this job. When triceps produce too much tension causing too slow
an elbow flexion, the elbow flexors can compensate that as antagonists.
According to the same author, agonist is defined as "a role played by a
muscle acting to cause a movement". The triceps are causing 'slow-down' of
the elbow flexion during the down-phase of pushup. Whthout the activation of
the triceps, he will simply collapse. If we stick to the definition, the
second statement is incorrect.
I'd like to get some comments or feedback on this issue from the readership.
I also posted this message to Biomch-L.
I WOULD APPRECIATE IT IF IN YOUR REPLY YOU MENTION YOUR AREA OF
EXPERTISE AS WELL. I'D LIKE TO SEE IF PEOPLE WITH DIFFERENT
BACKGROUNDS SHARE DIFFERENT VIEWS ON THIS.
-------------------------------------------------------------------
I posted this message to both Biomch-L and Sportscience and have received
about 15 responses so far. In order not to violate the message size limit of
both lists I compiled and put the individual replies at
http://www.cs.bsu.edu/~ykwon/miscellaneous/antagonist.htm.
Here are some of the observations from the replies and my thoughts:
1. The majority of the replies, with few exceptions, either supported my
view or at least mentioned the limits of the conventional anatomy-oriented
definitions of agonist & antagonist.
2. The view of the author of the textbook I am using for my undergraduate
Kinesiology course can not correctly address the 'ANTAGONISTIC RELATIONSHIPS
AMONG THE MUSCLES' when the intention of motion is to oppose the effects of
the external forces such as gravity. Muscles only produce tensions. When the
agonists produces too much tension or when the joint angle reaches the
extreme of the joint range of motion, the antagonists will produce tensions
to control or slow down the joint motion for fine control and safety. I
believe the agonist-antagonist issue is more than just to start motion
concentrically or to slow down a motion eccentrically. It implies the
control and safety mechanism in using the muscles. Antagonists will remain
relaxed unless their involvement is necessary for safety and control.
3. We may generally define the agonist as the main muscles which are
responsible for the intended motion of the joint, regardless of the type of
activation (concentric or eccentric). Technically, the agonist may be the
muscle group which generates the dominant net joint torque in relation to
the intention of the motion. The antagonists are the muscles which oppose
the action of the agonists. We may have to use a different approach to
explaining this issue to the undergraduate students who don't have much
biomechanics background, but still in this context.
4. The energy-oriented view is no different from the author's view,
especially in a single-joint muscles since single-joint muscles that produce
tension through eccentric contraction do negative work. The only difference
is in the case of two-joint muscles. A two-joint muscle may do a negative
work at a joint while it actually undergoes concentric contraction. But this
work-oriented view still can not effectively address the antagonistic
relationships among the muscles.
5. There are some additional issues such as two-joint muscles, multiple
degrees of freedom, and the location of the muscles. Firstly, two-joint
muscles may play one role in one joint and another in the other joint,
depending on the situation. Secondly, we may have antagonistic relationships
among the muscles for each possible joint motion at a joint. Thirdly, the
antagonists may not necessarily have to locate at the opposite side of the
joint to oppose the agonists in the cases such as pronation/supination. We
will have to focus on the functional role of the muscles rather than the
location in this case.
It was good to learn that there are some textbooks available which address
this issue in the right direction.
Cheers!
Young-Hoo
-------------------------------------------------------------------
- Young-Hoo Kwon, Ph.D.
- Biomechanics Lab, PL 202
- Ball State University
-
- Phone: +1 (765) 285-5126
- Fax: +1 (765) 285-9066
- E-mail: ykwon@cs.bsu.edu
- Homepage: http://www.cs.bsu.edu/~ykwon/
-------------------------------------------------------------------
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To unsubscribe send UNSUBSCRIBE BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://www.bme.ccf.org/isb/biomch-l
-------------------------------------------------------------------
About two weeks ago, I posted a message regarding the definition of
'antagonist'. I am grateful to all the individuals who spent their precious
time to respond to my message.
First, here is the original message:
---------------------------------------------------------------
According to the textbook I am using for my undergraduate Kinesiology
course, 'antagnist' is defined as "the role played by a muscle generating
torque opposing that generated by the agonists at a joint". Then it goes,
"When a muscle opposes a movement at a joint through development of
eccentric tension, it is acting as an antagonist." I witnessed similar
statements in some other textbooks I happened to possess. But I believe
there is a discrepancy between these two statements.
The definition implies that the antagonists opposes the agonists for fine
control of the movement and safety. When the agonists produces too much
tension or when the joint angle reaches the extreme of the joint range of
motion, the antagonists will produce tensions to control or slow down the
joint motion for fine control and safety since muscles produce tension only.
When the agonists contract concentrically, it is obvious that the
antagonists should contract eccentrically to slow down the joint motion. So
both statements above seem to agree. But what about the eccentric
contraction of muscles due to external load such as gravity?
Let's imagine some one is doing pushups. The triceps contract concentrically
during the up-phase, but eccentrically during the down-phase. According to
the second statement above, the triceps are the agonists during the
up-phase, but the antagonists during the down-phase. Which group of muscles
are the agonists in the down-phase then? Since the elbow flexion during the
down-phase is basically caused by the gravity, the elbow flexors can not be
the agonists. So the definition does not hold here.
Here is my view:
We can view the triceps as the agonists in both phases? The main job of
the muscles which the man intended during the down-phase was to slow down
the elbow flexion against the torque produced by gravity. Triceps are
undertaking this job. When triceps produce too much tension causing too slow
an elbow flexion, the elbow flexors can compensate that as antagonists.
According to the same author, agonist is defined as "a role played by a
muscle acting to cause a movement". The triceps are causing 'slow-down' of
the elbow flexion during the down-phase of pushup. Whthout the activation of
the triceps, he will simply collapse. If we stick to the definition, the
second statement is incorrect.
I'd like to get some comments or feedback on this issue from the readership.
I also posted this message to Biomch-L.
I WOULD APPRECIATE IT IF IN YOUR REPLY YOU MENTION YOUR AREA OF
EXPERTISE AS WELL. I'D LIKE TO SEE IF PEOPLE WITH DIFFERENT
BACKGROUNDS SHARE DIFFERENT VIEWS ON THIS.
-------------------------------------------------------------------
I posted this message to both Biomch-L and Sportscience and have received
about 15 responses so far. In order not to violate the message size limit of
both lists I compiled and put the individual replies at
http://www.cs.bsu.edu/~ykwon/miscellaneous/antagonist.htm.
Here are some of the observations from the replies and my thoughts:
1. The majority of the replies, with few exceptions, either supported my
view or at least mentioned the limits of the conventional anatomy-oriented
definitions of agonist & antagonist.
2. The view of the author of the textbook I am using for my undergraduate
Kinesiology course can not correctly address the 'ANTAGONISTIC RELATIONSHIPS
AMONG THE MUSCLES' when the intention of motion is to oppose the effects of
the external forces such as gravity. Muscles only produce tensions. When the
agonists produces too much tension or when the joint angle reaches the
extreme of the joint range of motion, the antagonists will produce tensions
to control or slow down the joint motion for fine control and safety. I
believe the agonist-antagonist issue is more than just to start motion
concentrically or to slow down a motion eccentrically. It implies the
control and safety mechanism in using the muscles. Antagonists will remain
relaxed unless their involvement is necessary for safety and control.
3. We may generally define the agonist as the main muscles which are
responsible for the intended motion of the joint, regardless of the type of
activation (concentric or eccentric). Technically, the agonist may be the
muscle group which generates the dominant net joint torque in relation to
the intention of the motion. The antagonists are the muscles which oppose
the action of the agonists. We may have to use a different approach to
explaining this issue to the undergraduate students who don't have much
biomechanics background, but still in this context.
4. The energy-oriented view is no different from the author's view,
especially in a single-joint muscles since single-joint muscles that produce
tension through eccentric contraction do negative work. The only difference
is in the case of two-joint muscles. A two-joint muscle may do a negative
work at a joint while it actually undergoes concentric contraction. But this
work-oriented view still can not effectively address the antagonistic
relationships among the muscles.
5. There are some additional issues such as two-joint muscles, multiple
degrees of freedom, and the location of the muscles. Firstly, two-joint
muscles may play one role in one joint and another in the other joint,
depending on the situation. Secondly, we may have antagonistic relationships
among the muscles for each possible joint motion at a joint. Thirdly, the
antagonists may not necessarily have to locate at the opposite side of the
joint to oppose the agonists in the cases such as pronation/supination. We
will have to focus on the functional role of the muscles rather than the
location in this case.
It was good to learn that there are some textbooks available which address
this issue in the right direction.
Cheers!
Young-Hoo
-------------------------------------------------------------------
- Young-Hoo Kwon, Ph.D.
- Biomechanics Lab, PL 202
- Ball State University
-
- Phone: +1 (765) 285-5126
- Fax: +1 (765) 285-9066
- E-mail: ykwon@cs.bsu.edu
- Homepage: http://www.cs.bsu.edu/~ykwon/
-------------------------------------------------------------------
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To unsubscribe send UNSUBSCRIBE BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://www.bme.ccf.org/isb/biomch-l
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