There is scarcely any need to describe the pain of myalgia, since almost every one has suffered either from lumbago, or from a stiff neck produced by cold. The pain is essentially the same in all cases; it is an aching actually felt either in or toward the tendinous insertions of the affected muscles, and sharply renewed by every attempted contraction of those muscles. The variations in the character and severity of the pains are really entirely due to the greater or the less opportunity for physiological rest which the muscle can obtain. Thus the most obstinate and the most severe, kind of myalgic pain is undoubtedly that of pleurodynia--pain in the intercostal muscles and their fibrous aponeuroses--a fact which depends on the incessant movements which these muscles are compelled to perform in the act of respiration. And next to this in severity and obstinacy are myalgias of the great muscles which are incessantly engaged in maintaining, by their accurately opposed contraction, the erect position of the spinal column and of the head. This rate of proportional frequency and severity, however, must be taken as strictly relative; _i. e._, it is correct upon the supposition that the different sets of muscles were equally worked and that the state of nutrition was equal in the different parents. It is otherwise when the conditions are reversed. Thus, the unfortunate cobbler or tailor, who sits for long hours in one cramped and bent posture, is continuously exerting his recti abdominales (probably suffering from an under-nutrition common to all his tissues) to a degree perfectly abnormal, and out of all proportion to the functional work he is getting out of any other part of his muscular system. The consequence is, that he comes to us complaining of acute epigastric, and sometimes pubic, pain, rising to agony when he assumes his ordinary sitting posture, and only reduced to any thing moderate by the most complete extension of the whole trunk in the supine posture.
There is no need to dilate at greater length upon the varieties in the symptoms of myalgia, according as it affects one or another part of the body. We must consider, briefly the different kinds of cause that produce it. The immediate source of the pain being, as we have seen, the sense of embarrassment in a muscle obliged to contract when unfit for the work, we have to ask what are the remoter causes that can produce this special unfitness for the work of contraction. They are three: (_a_) Overlabor pure and simple (_i. e._, in proportion to the existing bulk and quality of the muscle); (_b_) cold, and especially damp cold, producing a semi-paralyzing effect on the vaso-motor nerves, and causing congestion and sometimes a little effusion among the fibres or within the sheath of the muscle; (_c_) fatty degeneration of muscle which is exposed to inevitable and incessant work. Either of these conditions may so disable the muscle that its unavoidable contractions will set up the myalgic state.