This last method of writing is the one mostly taught in the public schools at the present day; and as a large number of muscles are brought into play, and as there is a more even division of the work, it is claimed that fatigue is not so soon complained of as in the first or older method.
The act of writing is primarily divisible, according to Poore,3 into three acts: 1st, the act of prehension; 2d, the act of moving the pen; 3d, the poising of the forearm and hand. The muscles concerned in the act of prehension are—the first two dorsal interossei, the opponens, abductor, and flexor brevis pollicis, and, to some extent, the flexor longus pollicis and the extensors of the thumb. The adductor should also be included in this enumeration.
3 G. V. Poore, Electricity in Medicine and Surgery, London, 1876.
The muscles employed in the movement of the pen differ somewhat according to the method of writing. In the finger movement Poore enumerates the following muscles as the ones used, viz.: flexor longus pollicis, extensor secundi internodii pollicis, flexor profundis digitorum, extensor communis digitorum, and also, to a lesser degree, the interossei.
In the second method of writing these muscles are comparatively quiet, except in making the letters which extend far above or below the line, while the muscles previously mentioned when describing this method are the ones called into play. The poising of the arm and hand is mainly accomplished by the supinator longus, supinator brevis, and possibly by the extensors of the thumb.
From a study of what has been written it will be seen that there are two classes of muscular actions concerned: 1st, the steady contraction of the muscles that poise the hand and hold the pen; and 2d, the intermittent contractions of the muscles concerned in moving the pen: both of these classes are equally important in the etiology of writers' cramp.
Chronic fatigue of the muscles is undoubtedly, in some cases, a precursor, if not a cause, of copodyscinesia, and, according to Poore,4 is occasionally the expression of hyperæmia or mild inflammation of a motor nerve. Acute local fatigue has symptoms which are well known to us all after having taken violent exercise, cramp and pain being the two most prominent ones.
4 “Writers' Cramp and Impaired Writing-Power,” Medico-Chirurgical Transactions, vol. lxi.
Any student who has dissected much has experienced the intense feeling of fatigue in the muscles required to hold the dissecting forceps, particularly when the spring is a little too strong. Much the same thing is noticed when one who has not been accustomed to write much is for some cause compelled to do so; he will probably notice that in a few hours he is exerting a greater amount of muscular force in pen-prehension than usual, and may even find that he is producing a disagreeable feeling in the distal phalanges by the pressure he is using; he will also probably be aware of a burning sensation between the shoulder-blades.