MadSci Network: Anatomy

Re: What causes the floating sensation felt after an isometric exercise?

Date: Wed Mar 30 11:26:35 2005
Posted By: Jens Peter Bork, M.D., Internal Medicine, Erlangen University Hospital
Area of science: Anatomy
ID: 1112068233.An

Dear Abby,

many thanks for your question regarding that floating sensation – This is a
tough one, and I am afraid I can only offer another speculation, not a
watertight answer.

Your own thought about the lactic acid having built up inside the muscle is
probably a point: During a long isometric contraction, the muscle is all
but shut off from the circulation, since its internal pressure is higher
than the blood pressure. This will lead to some accumulation of lactic
acid. Also, there may have been a very slight trauma to some muscle fibers
if you really pushed hard – all that may well lead to a sensation of
tenderness inside the muscle. 

But „floating“...? Well, here is another thought: You might already know
about the phenomenon of muscle tone. This is a constant activation of
muscle activity which is present  even when the muscle is not engaged in
any conscious movement. Muscle tone is regulated largely on an unconscious
level – We would constantly be falling over if we had to actually think
about how to keep ourselves in the balance sitting, standing up, or running
 – the unconscious regulation of the tone in our leg and spinal column
muscles takes care of that. 

Now muscle tone is not only present in those muscles that are constantly
engaged in some stationary activity (e. g., helping us stay in the balance
when standing). Tone is also present in the muscles that you would
ordinarily consider to be completely „unemployed“ – for example, the
muscles in your arm when the arm hangs freely from the shoulder in a
relaxed position. This tone, while being amenable to regulation by our
consciousness (think of certain relaxation techniques, for example), is
also largely regulated unconsciously. The presence of high general muscle
tone may be responsible for you „feeling tense“ before an exam or after a
hard day at school. But even in very “relaxed” circumstances, a muscle is
never totally relaxed.

Muscle tone may be the solution to your question. We do know that exertion
induces higher general muscle tone. I think your „floating“ sensation
resulted form the fact that after those strenuous 30 s, your general muscle
tone was very high, especially in the muscles that actually took part in
the exercise. So while you willed your muscles to relax, they did not quite
do this, and a high tone was preserved – and since the muscles lifting the
arm took part in the exercise, they probably did lift your arms a bit
afterwards (or at least, they let your arm hang not limply but tautly from
your shoulder) – and that was the „floating“ sensation. 

So I hope this helps – Tell your biology teacher that the Mad Scientist did
not know the answer himself and that he could only offer some qualified

By the way, if you (or your biology class) want to do an experiment on
muscle tone, here is one: Muscle tone determines the intensity of our
tendon reflexes (the ones a doctor elicits with his small rubber hammer
banging on muscle endings). The higher the tone, the more vigorous the
reflectory response. Try this. Sit on a bench or table at a height that
allows your lower legs to hang freely from the knee, and have a friend or
teacher do the patella reflex. [You do not need a rubber hammer, it can
also be done with edge of the outstretched hand or any „top-heavy“
instrument with a reasonably soft tip. You can take a regular hammer and
wrap the metal top in a few layers of cloth. The important thing is that
the strike is vigorous and elastic but does not hurt. The place you have to
hit is the somewhat elastic gap between the lower end of the patella and
the upper end of the shin]. If you manage a relaxed position, the patella
tendon reflex will probably be moderately vigorous. Now do the following
maneuver: Staying in that position, form a „hook“ with the flexed fingers
of both hands; interlock your hands; and try to pull the two „hooks“ apart
as  strongly as you can for 5 – 10 s. Then try the patella tendon reflex
again, and you will notice how much more vigorous it is. This trick is
known as „Jendrassick‘s maneuver“ (Ernö Jendrassick, Hungarian physician,
1858 – 1921) and is a way to beef up flabby reflexes (for example in older
people, in states of diminished consciousness, or in people under the
influence of muscle-relaxing drugs) in order to test for pathologic phenomena. 

References: The general things about muscle tone can be found in the
General Principles section of any Anatomy book. It might help to look up
the subject in a Sports Sciences book on muscle training – Regulation of
muscle tone is an issue in workout schedules, etc. 

Maybe you can tell me through the MadSci network how the experiment worked
out – Yours truly 
Jens Peter Bork

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