PUZZLE & PARADOX 113:

FURTHER COMMENTS ON ECCENTRIC ACTION

My original PP113 on eccentric action drew comments concerning the
observation that greatest EMG activity usually accompanies eccentric muscle
action, which should imply that greatest muscle tension should occur during
eccentric action.

Actually, even greater EMG activity can occur under explosive isometric
conditions which characterise the rapid termination of an eccentric action (as
occurs during the coupling phase between eccentric amortisation and the
rebound concentric phases in plyometrics). Dr Verkhoshansky and I discuss
this situation in detail in our textbook, 'Supertraining'.

Even if it were entirely correct that maximal EMG activity occurs during
eccentric action, this does not necessarily mean that the associated muscle
tension should be the greatest. This might simply imply that greater electrical
activity is being produced because acute or short-term fatigue is tending to
reduce the maximum tension already reached during the isometric action
directly preceding the eccentric action. Greater EMG activity is not
necessarily associated with the efficient, maximal or optimal production of
muscle tension, since the phenomena of spurious muscle tension and overflow
are well known. Electrical activity may also increase in an attempt to sustain
muscle tension when fatigue or failure processes begin to intervene.

Some comments still suggest that maximum eccentric action produces greater
muscle tension than isometric action, simply because one can lower or slowly
resist a load which is some 30-40% greater than that which can be held
statically. This argument has been propounded by strength authorities and
physiologists for many years, even though basic logic apparently contradicts
this popular belief.

Let us examine this issue once again from a simple engineering viewpoint.
Suppose we wish to determine in a laboratory the maximum force or torque
which a given motor can produce. One way which we could use is to keep on
adding a load until the motor could no longer move. When all movement
ceases, we may deduce that maximal loading conditions have been achieved
and that the tension in the cable supporting the load is now at a maximum for
that given motor. Any further attempt to load the motor further would
undoubtedly result in :

(a) damage to the motor, or
(b) rupture of the cable

For (a) not to occur, the motor would have to safely be able to produce greater
power.
For (b) not to occur, the cable would have to be structurally strengthened.

Let us now apply this analysis to the case of muscle action. When the muscle
can no longer produce enough force to overcome the added load, then external
joint action will cease and maximal strength capabilities and maximal muscle
tension for that muscle group will have been reached. Thus, maximal muscle
tension for that muscle group will be reached under isometric conditions,
unless:

1. that muscle group can somehow spontaneously increase its structural
strength, which is impossible.

2. that muscle group can be compelled to exceed its normal isometric
maximum output, provided that the greater force produced does not
exceed the maximal strength of the muscle tissue. This is what is
presumed to happen under eccentric conditions in general. If this is true,
then it implies that maximal muscle tension is not necessarily reached
under gradually reached isometric conditions.

This is an entirely reasonable deduction, since any sensibly-designed
structure allows for extraordinary or unexpected operating conditions (in
engineering, this refers to designing a device or structure with a certain
'Safety Factor' to permit safe operation under conditions which exceed
known maximal conditions). In the case of living muscle, this would
mean that maximal tension probably would not be attainable under
conditions where the load can be controlled voluntarily by relatively slow
activation of the muscles (unless one is mentally trained to be able to
produce a voluntary maximum which equals one's involuntary maximum,
an achievement which is attained by very few individuals).

In other words, it would appear to be unlikely that maximal muscle tension
would be produced under 'normal' isometric, concentric or eccentric
conditions, where one can consciously intervene by modulating muscle tension
by response to perceived feedback (or automatically via Golgi tendon and
other reflex processes). However, if the body and its joints are exposed to
sudden increases in loading, the muscle may be stimulated to produce closer to
maximum power output. This limiting condition tends to occur under
involuntary conditions when survival of some or all of the body is of
paramount importance.

This survival may take place in two diametrically opposite ways:

1. Inhibition of any further increase in muscle tension (so that one is forced
to lower or stop striving against the load). This action is commonly
associated with greater activation of the Golgi Tendon Organ and with
astute training may be overridden to a certain extent.

2. Stimulation of further increase in muscle tension. This tends to occur
most readily under reactive or rebound conditions such as those
encountered in running and jumping. This process forms the foundation
of the entire system now known as PLYOMETRIC TRAINING. It
should be pointed out that PLYOMETRIC ACTION, which occurs quite
naturally when the Rate of Force Development (RFD) is great, is not the
same as plyometric TRAINING, which is a system of drills using
exercises which naturally produce various plyometric actions (see Siff &
Verkhoshansky 'Supertraining' Ch 5).

It should also be noted that the duration of operation under maximal conditions
is another important factor which determines safety and effectiveness.
Maxima are not maintained for prolonged periods, but are achieved for limited
periods which solve the emphemeral survival problem. One then obviously
has to examine the link and differences between the different classes of fatigue
and failure. We also have to scrutinise how the different types of hypertrophy
(sarcomere and sarcoplasmic - see 'Supertraining' Ch 1.12), strength and
muscle endurance are influenced and developed by the type, intensity, duration
and pattern of muscle action.

All of this shows that the issue of muscle tension and muscle activation during
isometric and all other types of muscle action is by no means as simple or basic
as is implied by some of the popular literature, many highly visible fitness
'experts' or by machine manufacturers.
_________________________________________________________



Dr Mel C Siff
School of Mechanical Engineering
University of the Witwatersrand
WITS 2050 South Africa
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