1) If you were handed a weight and you tried to prevent
it from falling but could not because it was too heavy, would
not the golgi tendon organ's inhibitory responses be greater
than the muscle spindles myotatic reflex?
I don't
believe so because of the reasons outlined in points 1 and 4
above - if there is an inhibitory effect it almost certainly
doesn't come from the GTO. However, my exact response would depend
on how much weight I was given. Assuming that the load was just
above my max for an isometric contraction the eccentric contraction
would be slow. In this case the spindles would be strongly activated
by the stretch and would deliver a powerful excitatory effect
to the motoneurone pool.
You may remember the previously quoted studies that indicate
that the sensory information from muscle is much more excitatory
than inhibitory during attempted isometric MVCs (when this feedback
is taken away the output from the spinal cord decreases by 30-40%).
I would imagine that this would be the same during slow eccentric
contractions with 105-130% of the maximum load.
If the load was extremely heavy (160-200% max) I would probably
drop it based on the feedback obtained from a number of sensory
organs, including the GTO. This information would arrive in the
brain and I would decide that resistance was futile. In this
case the GTO (along with other sensors) provides the feedback
necessary for a safe decision to be made but does not actually
inhibit effort during an MVC.
Whilst on the topic it must be said that muscle activation
is incomplete during eccentric MVC's (Amiridis et al., 1996;
Westing et al., 1990), but the reason why is a mystery. For the
reasons stated above it seems unlikely that the GTO would exert
a powerful enough effect to significantly limit muscle activation.
2) If you were performing a bench press and paused the
bar at the chest, would you not inhibit the muscle spindles reflex.
You have noticed that it is much more difficult to push the weight
back up after a pause. It seems the muscle spindle reflex is
greatest immediately at end of the eccentric contraction, or
change in direction. If this is true, would there not be phases
of a weight training exercise that the golgi tendon organ inhibitory
reflex could be potentially greater than the muscle spindles
excitatory reflex - for example, the middle of the concentric
contraction?
The contribution of the stretch reflex would be smaller with
the pause, however for the same reasons (1 & 4) it is doubtful
that the inhibition provided by the GTO is powerful enough to
provide much inhibition. Furthermore you do not eliminate the
stretch reflex with a pause - the excitatory input from type
Ia and type II fibers (from muscle spindles) is still high during
maximal isometric and concentric contractions (eg. Hutton and
Atwater, 1992). In these cases the spindles are stretched by
the action of the intrafusal fibers which are powerfully activated
(by the gamma motoneurones) during MVC's.
The pause interferes with performance mainly because the mechanical
energy stored within the cross-bridges is allowed to dissipate.
3) Does your research negate the golgi organs role in Proprioceptive
neuromuscular facilitation (PNF) stretches.
PNF techniques
and the sometimes dodgy theories behind them are covered well
by Hutton in chapter 2c of Strength and Power in Sport that you
quoted Komi from. Hutton suggests that the GTO does not play
the role that many people think and provides some convincing
evidence for his arguments.
It is most everyone's experience who perform PNF stretches
that after pushing against an immovable force, a muscle can be
stretched significantly more through reciprocal innervation.
Does this not demonstrate that the golgi tendon organ inhibitory
reflex can be greater than the muscle spindles excitatory reflex?
No - it demonstrates that PNF stretches are a valuable means
of increasing flexibility but it demonstrates nothing with regard
to the GTO's involvement because numerous other factors could
equally well explain these observations.
4) In accordance with your studies, is this still true?
During running, don't we experience the effects of both the golgi
tendon organ and the muscle spindle. On impact of the heel: golgi
tendon organ's inhibition to the dorsal flexors and excitation
of its antagonist (plantar flexors). As the body moves forward,
weight is shifted to the forefoot stretching the plantor flexors:
muscle spindles' excitation to the plantar flexors.
You are probably on the right track here because reflexes
do take a significant role in gait which is automated to a significant
extent. MVCs are not automated to the same extent.
5) In what movement contexts does the golgi tendon organ
exhibit an excitatory influence to both the muscle that they
innervate and that muscle's synergists (re: Pratt et al., 1995)
When load bearing - an increase in load is met by a reflex
that excites the extensor muscles of the weight bearing limbs
(this is aka the loading reflex). Thus when it is desirable for
an increase in load to be met by an increase in extensor force
the GTOs input is processed differently than when an increase
in force is not desirable.
6) As reported by Kreighbaum's Biomechanics text: Komi
(1992) proposed the decreasing the sensitivity of the Golgi organs
through strength and power training... ...If decreasing the Golgi
organs sensitivity is possible, would not increasing its sensitivity
also be possible?
Komi made the proposal but this is not evidence that the adaptation
actually occurred. I don't know of any research that can back-up
his guess. Neither did Hutton in 1992 (Hutton and Atwater, 1992).
Interesting that Hutton contributed to Komi's book just before
he discredited Komi's claim in another article.
7) As far as proprioceptive functions, would you disagree
that golgi tendon organs are sensitive detectors of tension in
their host muscle? As sensors of degrees of tension, would they
not be important contributors to fine motor control as well as
protective agents?
No I would not disagree with the statement that the GTOs are
detectors of tension. However, whether they protect us in the
manner that you suggest is doubtful for reasons 1 & 4. They
may, however, (along with a number of other receptors such as
pressure receptors in the skin and joints) protect us in the
manner outlined in answer to question 1. (ie. they may let us
know when it is wise to jump out of the way).
It is important to consider that much of the neurophysiological
research that influenced strength and conditioning (S&C)
researchers and practitioners in the early days was performed
on animal preparations in which certain parts of the nervous
system were surgically removed. For example, much of Houk's work
on the GTO was done with cats who had had their spinal cords
cut or certain parts of the brain destroyed. Consequently, this
work showed how the spinal reflexes could work in the absence
of voluntary control and without the addition of longer loop
reflexes that involve the brain. The picture of the GTO that
emerged from these studies is significantly different from that
which is emerging from more recent studies on intact animals
and humans.
Hope this helps. Best regards.
Tony Shields
