|MadSci Network: Anatomy|
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 speculation. 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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