Electromyographic study of the brachioradialis muscle

Our previous study (Machado de Sousa et al., '58) on some human forearm muscles during pronation and supination, showed us that our knowledge about the actual function of the brachioradialis is still insufficient. This is also true for almost all skeletal muscles, because most of our present knowledge about their functions is based mainly upon anatomomechanical studies or are influenced by the electrophysiologic studies of Duchenne (1867). But such studies do not show the behavior of muscles in the living subject during voluntary movements. For the appraisal of muscular activity in the living when voluntary movements are carried out, electromyography has been used. Many muscles have already been studied by this method, but there are very few data referring to the brachioradialis (Basmajian and Latif, '57). The morphology of this muscle is well known (Testut, 1884); Le Double, 1897; Chudzinski, 1898; Anthony and Hazard, '05; Monteiro, '23; Liaras and Bourgeon, '41); Oliveira Netto, '42), but there are conflicting views concerning its actual function. Duchenne states that the electrical stimulation of the brachioradialis determines strong flexion of the elbow and puts the hand in mid-position between pronation and supination. This statement is repeated in several text-books. Furthermore, besides the action of flexion, Duchenne points out only the role of this muscle in carrying out pronation when the forearm is in supination, and he criticizes the name "supinator longus" because this muscle produces only the opposite movement. But, on the contrary, some authors ascribe to that muscle the action of flexion of the elbow and supination of the forearm (Lambertini, '46; Rouvihre, '48 and Paturet, '51); and surely interpreting the action of carrying the hand to a midposition between pronation and supination referred to by Duchenne, others still admit that this muscle has a triple action, that is, flexion, pronation and supination of the forearm (Poirier and RouviGre, in PoirierCharpy, '12; Favaro, in Pensa and Favaro, '33; Chiarugi, '48; Lockhart, in Cunningham, '49; Testut-Latarjet, '28; Orts Llorca, '44; Braus, '54; Rauber-Kopsch, '55 and Woodburne, '57). The brachioradialis is considered as only a flexor of the elbow by Frohse and Fraenkel in Bardeleben ('08); in Gray, (by Davies, '58) and (Goss, '59); Lockhart, Hamilton and Fyfe ('59), as well as by Walmsley in Quain ('23), who nevertheless does not exclude definitely the possibility of its participation in the rotatory movement of the forearm. Among the special publications on the action of muscles in general, the brachioradialis is supposed to flex, to prone and to supine the forearm (Roud, '13), or, it is supposed to be in activity only during the rotatory movements of the forearm and not in its flexion (Mackenzie, '40). At last, some authors suppose the muscle to be only a flexor of the forearm, this flexion being stronger with the hand in pronation (Hoepke, '49; Orts Llorca, '44; Braus, '54). In their electromyographic study on the flexors of the elbow Basmajian and Latif observed that the brachioradialis did not show any activity during the slow flexion of the elbow, except when the forearm was semipronated. With a load of two pounds, the muscle was active during the