Dear Dr.
About muscle Classification there some Kinesiologic controversies with the
V.M.O.
Do you consider this muscle as Tonic or Phasic?
Best wishes all.Thanks.
Sergio Velasquez V.
[log in to unmask]
Medellin,Colombia
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, April 28, 2001 8:30 AM
Subject: Agonists and Antagonists?
> The use of the terms, "agonist" and "antagonist" is fraught with
> misunderstanding and misapplication. Although "agonists" traditionally
refer
> to the "prime movers" in a given joint action and the "antagonists"are
> understood to be those muscles which act in the opposite direction to the
> agonists, it is incorrect to presume that, when a given joint is moving,
the
> antagonists are always opposing the agonists. As I pointed out in other
> letters on concontraction and ballistic action, antagonists sometimes are
not
> antagonists at all - they may simply be inactive spectators during much of
> the joint action. That is a major reason why Basmajian, for one, suggests
> that all muscles should rather be thought of as "synergists", or
co-workers
> who cooperate in specific patterns, as the movement need arises.
>
> Thus, while the triceps may be the anatomical or STRUCTURAL antagonists to
> the agonistic biceps, they are not necessarily the FUNCTIONAL antagonists
to
> every action involving the biceps or elbow flexors, in general.
Similarly,
> the hamstrings do not necessarily act antagonistically to the quadriceps
in
> all actions involving the knee joint, especially during explosive
movemenst
> such as running, jumping and kicking. Any marked concurrent contraction
of
> the hamstrings while the quadriceps are contracting powerfully in these
> situations would rapidly slow down the knee extension or lead to hamstring
> injury. The antagonists come into meaningful play only when the end stage
> movement of the joint has to be halted, not throughout the movement. That
is
> the nature of ballistic movement.
>
> Here is some more information on agonists and antagonists:
>
> -------------------------------------------------------
>
> CLASSIFICATION OF MUSCLE ACTIONS
>
> [Siff MC "Supertraining" 2000 Ch 1.8 ]
>
> In producing the various directions of movement, many muscles are
> simultaneously involved in controlling the action from its beginning to
its
> end. This orchestration of diverse contributing muscles has led to
different
> roles being allocated to each muscle group. One of the typical
classification
> schemes recognizes the following traditional roles:
>
> * Agonists: Muscles acting as the so-called prime movers of the action.
> Prime movers produce the most significant contribution to the movement,
while
> assistant movers play a more secondary role in assisting this prime
action.
> Some authorities recognise emergency muscles as a special class of
assistant
> movers which come into play only when maximal force must be generated
during
> a particular movement. In physiotherapy, the phenomenon of assistant
movers
> being recruited by significant increases in loading is referred to as
> overflow. The value of training periodically against near maximal or
maximal
> resistance then becomes obvious.
>
> * Antagonists: Muscles acting in direct opposition to the agonists. As
> emphasized by Basmajian (1978), this action does not necessarily accompany
> every agonistic contraction, but only under certain circumstances.
Central
> nervous processes are sufficiently refined to control agonist activity
> without routine reliance on opposition by antagonists. After all, in
> engineering situations it is rarely necessary to use two motors in
opposition
> to offer sophisticated control of any movement. All that is necessary is
a
> single sufficiently powerful motor with rapid feedback processes to ensure
> accuracy, control, appropriate force and appropriate speed throughout the
> defined movement range.
>
> Moreover, it is important to note that reciprocal inhibition of the
> antagonist usually occurs whenever an agonist is strongly activated (see
> 3.5.3). In other words, the antagonist invariably relaxes when the
agonist
> contracts, except when the action is extremely rapid and some
'antagonists'
> come into play to prevent joint damage due to the large momentum of the
> moving limb. The inappropriate activation of 'antagonists' to oppose
> strongly contracting agonists, however, is recognised as one of the causes
of
> musculoskeletal injury. For instance, the hamstrings can rupture if they
> contract to oppose the quadriceps while an athlete is sprinting or
kicking.
> Russian researchers have shown that antagonist inhibition occurs most
readily
> during rhythmic activity associated with motor learning.
>
> So-called 'antagonists' may act continuously or in periodic spurts
throughout
> a movement. Moreover, the presence of antagonist activity may be due
to
> motor learning and not inherent reflexes. Sometimes, the existence of
> antagonistic activity is a sign of unskilled movement or nervous
abnormality.
> Clearly, the automatic labelling of specific muscle actions as
antagonistic
> needs to be tempered with caution, unless confirmed by careful
> electromyography (recording of electrical signals from the muscles).
>
> * Stabilisers: Muscles stabilising or supporting a body segment
statically
> or dynamically while other muscles carry out a movement involving other
> joints. During static stabilisation, the muscles either contract
> isometrically or quasi-isometrically (very slowly). An example is the
action
> of the spinal erectors (erector spinae) during pushups. They maintain an
> isometric contraction to prevent the spine from hyperextending (sagging)
> while the pectoral and anterior deltoid muscles produce the up and down
> movement of the upper body relative to the ground. During dynamic
> stabilisation, the muscles are in continuous contraction while
simultaneously
> carrying out a mobilising role. For instance, during running and walking,
> the quadriceps contract not only to extend the knee, but also to stabilise
it
> during the ground contact phase of each stride. Stabilising muscles often
> augment the action of ligaments, which are passive stabilisers (unlike
> muscles, which are active stabilisers).
>
> In keeping with the concept of emergency muscles described earlier, one
may
> also recognise the existence of assistant or emergency stabilisers which
are
> recruited to assist the 'prime' stabilisers during very intensive effort
by
> the prime and assistant movers. This principle is used in rehabilitation
by
> physiotherapists to recruit 'lazy' muscles.
>
> * Neutralisers: Muscles counteracting the unwanted actions of other
> muscles by tending to produce opposite movements. An example is offered
by
> situps, in which the internal and external obliques contract
simultaneously
> to produce trunk flexion. Singly, these muscles tend to produce lateral
> flexion and rotation of the trunk. Simultaneously contracting, they
oppose
> one another to cancel these movements and thereby assist the rectus
abdominis
> muscles in producing pure trunk flexion. Similarly, the anterior and
> posterior heads of the deltoid muscles neutralise one another's tendencies
to
> elicit medial/lateral rotation and horizontal flexion/ extension, thereby
> assisting the medial head in producing pure abduction (raising of the arm
> laterally).
>
> Variations on these categories exist, such as the division of muscles into
> two classes: synergists, which cooperate to produce a movement, and
> antagonists which act in opposition to the direction of movement.
However,
> it must be emphasized that all muscles operate synergistically in the
normal
> person; they all co-operate by contributing forces in the most
appropriate
> directions to produce the desired motion, although not necessarily with
> maximum efficiency. It is preferable to remember that all muscles
interact
> to produce the two fundamental characteristics associated with all human
> movement: stability and mobility (see 1.7.4). To do this, the same muscle
> may act as a mover at one time and a stabiliser at another. It is
> inappropriate to identify a muscle as one of the above types under all
> circumstances. Accurately speaking, a muscle may only be identified as
> carrying out a specific role in a specific situation. Thus, it is
imprecise
> to refer to specific muscles as being agonists, antagonists, stabilisers,
> synergists and so forth: it is more accurate to state that each muscle
plays
> a specific role at a given moment (or during a certain movement phase) in
a
> given situation.
>
> Muscles are also categorised as being tonic (postural or anti-gravity) to
> offer stability and resist gravity, or phasic (dynamic) to provide
movement.
> Tonic muscles are usually penniform, contain a higher proportion of slow
> twitch muscle fibres, generally cross only one joint, lie deeper below the
> surface and perform extensor actions including abduction or lateral
rotation.
> Phasic muscles usually occur more superficially, contain more fast
twitch
> muscle fibres, often cross more than one joint and perform flexor
functions,
> including adduction and medial rotation.
>
> -------------------------------------
>
> Dr Mel C Siff
> Denver, USA
> http://groups.yahoo.com/group/Supertraining/
>
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