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34 Ins. Counsel J. 455 (1967)
Quantitative Electromyographic Investigation of the Spasm Theory of Muscle Pain

handle is hein.journals/defcon34 and id is 457 raw text is: INSURANCE COUNSEL JOURNAL Quantitative Electromyographic Investigation Of The Spasm Theory Of Muscle Pain HERBERT A. DE VRIES, PH.D. Los Angeles, California T WO types of pain are associated with severe muscular exercise: 1) pain during and immediately after exercise which may persist for several hours, and 2) a localized soreness which usually does not appear for 24 to 48 hr. The first is probably due to the diffusible end prod- ucts of metabolism acting upon pain re- ceptors.9 The second is widely attributed to torn muscle fibers and/or connective tissue.1'1,22,2 It is the second type, the de- layed, localized pain or soreness, with which this paper is concerned. The hy- pothesis of torn tissues was probably first presented by Hough at the turn of the century. It must be emphasized that he presented no direct evidence for this theory and that, furthermore, other hypotheses could explain his data equally well. How- ever, this hypothesis has gained* acceptance over the years in spite of an apparent lack of evidence found by either Hough or other investigators since that time. It must be considered somewhat unrea- sonable to postulate structural damage to a tissue, caused by the very function for which it is specifically differentiated. A more reasonable hypothesis is suggested by observation of typical muscle fatigue curves. In addition to the decrement in amplitude of contraction, an increasing inability to achieve complete relaxation is typical and, significantly, this may end in contracture. For these reasons, the writer has suggested a seemingly more attractive hypothesis: The delayed, localized sore- ness which occurs following unaccustomed exercise is caused by tonic localized spasm of motor units, whose number varies with the severity of pain. A rationale based upon considerable physiological evidence can be constructed to support this hypothe- sis on a sound theoretical basis. First, it has been shown that exercise above a minimal level causes some degree of ischemia in the active muscles.'9,21 Sec- *Reprinted with permission from the AMERICAN JOURNAL OF PHYSICAL MEDICINE, Vol. 45, p. 119. ond, it is well known that ischemia causes muscle pain. This pain probably occurs by means of the transfer of P-substance5 across the muscle cell membrane into the tissue fluid. From this fluid it gains access to pain endings. Third, the pain brings about a reflex, tonic muscle contraction, which prolongs the ischemia and thus be- gins a vicious cycle. Evidence has been presented20 to support the concept of spasm caused by painful stimuli. If this hypothe- sis proves tenable, it could be logically generalized to apply to other types of clinically-observed pain involving skeletal muscles. It has already been suggested by others that: The pain inducing nature of sustained muscle contraction is particularly important because many pains and aches in organic disease and anxiety states result from it. The underlying mechanism is probably diminished blood flow caused by compression of blood vessels within the muscles .. (Fulton,'° p. 363). Because the vicious cycle hypothesized above has a vulnerable aspect allowing simple experimental testing and providing an immediate clinical approach to relief from such muscle pain, the spasm theory becomes even more attractive. Most com- petitive swimmers and swimming coaches are well aware of the fact that swimmer's cramp (Gastrocnemius) is promptly re- lieved by gently forcing the involved mus- cle into its longest possible state and hold- ing it there for a moment. This relief of cramp by stretching has also been demon- strated experimentally.20 It seems likely that the inverse myotatic reflex originating in the Golgi tendon organs is the basis for this phenomenon. To test the spasm theory, several lines of investigation have been pursued in the writer's laboratory. First it was shown that a significant degree of prevention could be provided against soreness from a standard- ized experimental exercise if the active muscle were stretched periodically.3 The stretching technique was developed to take July, 1967 Page 455

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