Dr M. C. Siff
09-04-1995, 12:15 AM
Here are a few more P&Ps for the week.

I look forward to seeing some puzzles or paradoxes from your
experience as well. The following are a few more of the PROPOSITIONS
(not facts!) that I use in teaching my students. They have to
discuss, find references or propose their own answers based on
existing theory. Your comments are invited.


17. Ballistic stretching may not be as well understood or as harmful
as has been claimed.

Ballistic stretching commonly is regarded as stretching performed
with bouncing or with the use of momentum to
extend one's normal range of movement. Little is ever said about the
state of the tissues involved during the process, which constitutes a
serious omission. The bouncing may be imposed either on relaxed
muscles or contracted muscles, the mechanisms and results in each
case being very different. One must also appreciate the differences
introduced by changing the rapidity of the bouncing, taking into
account the fact that explosive bounces on contracted muscles may
constitute what is known as 'PLYOMETRIC' ACTION (not plyometric

This then necessitates considering the roles played by
elastic energy, eccentric muscle action and reflex processes. On the
practical side, we note that ballistic actions involving both relaxed
and contracted muscles occur all the time in most sports, in most
cases sparing energy and improving efficiency without causing injury.
Yet most 'experts' on stretching advise against the use of ballistic
stretching, especially on contracted muscles. Comment.

18. Reliance on the hyperbolic Force-Velocity curve to understand
the relationship between training load and speed may lead to serious
misunderstandings of strength training.

The well-known hyperbolic F-V curve shows that FORCE DECREASES as the
movement velocity increases and increases as the movement velocity
decreases. Or does it show that the VELOCITY INCREASES as the force
decreases (and conversely that the velocity decreases as the force
increases)? Are these just inverse ways of stating the same thing or
is one of these statements incorrect or misleading?

Let us now take this curve out of the laboratory where it was derived
and take it into the world of real sport where movement efficiency
depends not only on rate of voluntary (or electrically stimulated
contraction), but also on the storage and release of elastic energy.
Does this standard F-V hyperbola still apply here? What about the
force-velocity relationships in the case of cyclic versus acyclic
activity, bearing in mind the fact that Russian scientists have found
at least two peaks in the cyclically-produced F-V curve? Let us also
consider the characteristics of the F-V curve when the action is
rapidly terminating eccentric. Comment on all of this.

19. Our understanding of bouncing squats may be incomplete or
incorrect.Most of us have been warned about the increased patello-
femoral force produced by bouncing at the lowest point of the squat
and the consequent risk of knee damage (to the joint, ligaments,
tendons etc). Elite Bulgarian lifters, however, maintain that it is
less dangerous and much more efficient to bounce in the squat when
one recovers from the lowest position of the Olympic snatch or clean.
They emphasise that knee injuries are more common among powerlifters
who squat SLOWLY to and from a HALF squat position with the aid of
protective knee wraps or bandages, compared with weightlifters who
bounce rapidly with unprotected knees out of a full squat, often
producing greater reactive forces as measured on a force plate.
Which viewpoint is correct and why?

20. Defining isometric muscle contraction simply as a static muscle
action is a misleading oversimplification that can confuse research
and training.

Firstly, do we know if the same muscle fibres producing
the isometric contraction are exactly the same or are they rapidly
and regularly relaxing and recruiting other fibres to maintain the
action? Next, there is not just one type of isometric action. One
has to take into account how rapidly the peak isometric force is
produced, since the activation curve and effects of fatigue will be
different for each situation. Russian scientists recognise at least
two types of isometric action: SLOW (gradual onset) isometrics and
EXPLOSIVE isometrics (which occurs during the coupling phase between
the eccentric amortisation phase and the concentric driving phase in

Furthermore, they distinguish between CONCENTRIC
isometrics (produced if the contraction is on the point of overcoming
a load) and ECCENTRIC isometrics (produced if the load is just about
to overcome the contraction). We must also remember that different
neural mechanisms are involved with motor activity at different
speeds and that the Russians explosive isometrics for speed and power
development. The torque (or force) - joint angle curves derived in
the laboratory are produced under slow isometric conditions and
cannot accurately be related to actions that involve explosive
isometrics. Most of the studies of the effects of isometric training
on muscle strength, power, hypertrophy and endurance have involved
only slow isometrics. How much of our research on isometrics is then
of definitive scientific or practical value?

Dr Mel C Siff
School of Mechanical Eng
University of the Witwatersrand
South Africa