Here is an extract from “Supertraining” that we discussed on some clinically
oriented groups a while ago. I felt it appropriate to repeat here, because
we often encounter spectacular claims about the magical power of some rather
dogmatic methods of ‘muscle testing’.

MUSCLE TESTING

Standard anatomical textbook approaches describing the action of certain
muscle groups in controlling isolated joint actions, such as flexion,
extension and rotation, frequently are used to identify which muscles should
be trained to enhance performance in sport. Virtually every bodybuilding
and sports training publication invokes this approach in describing how a
given exercise or machine ‘works’ a given muscle group, as do most of the
clinical texts on muscle testing and rehabilitation.

The appropriateness of this tradition, however, recently has been questioned
on the basis of biomechanical analysis of multi-articular joint actions
(Zajac & Gordon, 1989). This classical method of functional anatomy defines
a given muscle, for instance, as a flexor or extensor, on the basis of the
torque that it produces around a single joint, but the nature of the body as
a linked system of many joints means that muscles which do not span other
joints can still produce acceleration about those joints.

The anatomical approach implies that complex multi-articular movement is
simply the linear superimposition of the actions of the individual joints
which are involved in that movement. However, the mechanical systems of the
body are nonlinear and superposition does not apply, since there is no
simple relationship between velocity, angle and torque about a single joint
in a complex sporting movement. Besides the fact that a single muscle group
can simultaneously perform several different stabilising and moving actions
about one joint, there is also a fundamental difference between the dynamics
of single and multiple joint movements, namely that forces on one segment can
be caused by motion of other segments. In the case of uniarticular muscles
or even biarticular muscles (like the biceps or triceps), where only one of
the joints is constrained to move, the standard approach is acceptable, but not
if several joints are free to move concurrently.

Because joint acceleration and individual joint torque are linearly related,
Zajac and Gordon (1989) consider it more accurate to rephrase a statement
such as “muscle X flexes joint A” as “muscle X acts to accelerate joint A
into flexion”. Superficially, this may seem a matter of trivial semantics,
but the fact that muscles certainly do act to accelerate all joints has
profound implications for the analysis of movement. For instance, muscles
which cross the ankle joint can extend and flex the knee joint much more
than they do the ankle.

Biomechanical analysis reveals that multiarticular muscles may even
accelerate a spanned joint in a direction opposite to that of the joint to
which it is applying torque.

In the apparently simple action of standing, soleus, usually labelled as an
extensor of the ankle, accelerates the knee (which it does not span) into
extension twice as much as it acts to accelerate the ankle (which it spans)
into extension for positions near upright posture (Zajac & Gordon, 1989).
In work derived from “Lombard’s Paradox” (‘Antagonist muscles can act in the
same contraction mode as their agonists’), Andrews (1985, 1987) found that
the rectus femoris of the quadriceps and all the hamstrings act in three
different ways during cycling, emphasizing that biarticular muscles are
considered enigmatic.

This paradox originally became apparent when it was noticed that in actions
such as cycling and squatting, extension of the knee and the hip occurs
simultaneously, so that the quadriceps and hamstrings are both operating
concentrically at the same time. Theoretically, according to the concept of
concurrent muscle antagonism, the hamstrings should contract eccentrically
while the quadriceps are contracting concentrically, and vice versa, since
they are regarded as opposing muscles.

Others have shown that a muscle which is capable of carrying out several
different joint actions, does not necessarily do so in every movement
(Andrews, 1982, 1985). For instance, gluteus maximus, which can extend and
abduct the hip, will not necessarily accelerate the hip simultaneously into
extension and abduction, but its extensor torque may even accelerate the hip
into adduction (Mansour & Pereira, 1987).

Gastrocnemius, which is generally recognised as a flexor of the knee and an
extensor of the ankle, actually can carry out the following complex tasks:

(a) flex the knee and extend the ankle
(b) flex the knee and flex the ankle
(c) extend the knee and extend the ankle

During the standing press, which used to be part of Olympic Weightlifting,
the back bending action of the trunk is due not only to a Newton III
reaction to the overhead pressing action, but also due to acceleration
caused by the thrusting backwards of the triceps muscle which crosses the
shoulder joint, as well as the elbow joint. This same action of the triceps
also occurs during several gymnastic moves on the parallel, horizontal and
uneven bars.

This back extending action of the triceps is counteracted by the expected
trunk flexing action of rectus abdominis and the hip exension action of the
hip flexors, accompanied by acceleration of the trunk by the hip flexors.

Appreciation of this frequently ignored type of action by many
multiarticular muscles enables us to select and use resistance training
exercises far more effectively to meet an athlete’s specific sporting needs
and to offer superior rehabilitation of the injured athlete.

Finally, because of this multiplicity of actions associated with
multiarticular complex movement, Zajac and Gordon stress a point made by
Basmajian (1978), namely that it may be more useful to examine muscle action
in terms of synergism rather than agonism and antagonism. This is especially
important, since a generalised approach to understanding human movement on
the basis of breaking down all movement into a series of single joint
actions fails to take into account that muscle action is task dependent.

References:

Andrews J G (1982) On the relationship between resultant joint torques and
muscular activity Med Sci Sports Exerc 14: 361-367

Andrews J G (1985) A general method for determining the functional role of
a muscle J Biomech Eng 107: 348-353

Andrews J G (1987) The functional role of the hamstrings and quadriceps
during cycling: Lombard’s paradox revisited J Biomech 20: 565-575

Basmajian J (1978) Muscles Alive Williams & Wilkins Co, Baltimore

Mansour J M & Pereira J M (1987) Quantitative functional anatomy of the
lower limb with application to human gait J Biomech 20: 51-58

Zajac F E & Gordon M F (1989) Determining muscle’s force and action in
multi-articular movement Exerc Sport Sci Revs 17: 187-230

Mel Siff
Denver, USA
Mel Siff Dot Com
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