Electromyography of the Pronator Muscles in the Forearm JOHN V. BASMAJIAN AND ANTHONY TRAVILL D e p a r t m e n t of A n a t o m y , Queen’s University, Kingston, Ontario, Canada In the past there has been no accurate authoritative information on the relative functional roles of the two pronator muscles, although it is true that their gross anatomy is adequately described in the standard textbooks. We felt that if such information were available, it would be of practical importance. Therefore, we carried out an electromyographic study of the pronator teres and the pronator quadratus in a series of volunteers, and found that the few remarks on function that are presently available in books are largely misleading. MATERIAL AND METHODS The pronator muscles of 8 young adult male subjects were investigated electromyographically. The apparatus and concentric needle electrodes used were the same as those that have been described earlier (Basmajian, ’57, 58). In brief, the apparatus consisted of a special multichannel electromyograph (fig. 1) that makes records on 35-mm photographic film from the faces of cathode-ray oscilloscopes, All the experiments were done in an electrostatically shielded room. Procedure. With the subject reclining comfortably and the outstretched upper limb supported on a table (fig. 2), a needle electrode was placed in each of the two pronator muscles in the following manner. A small area of skin was anesthetized with procaine (1% ) and the electrode was inserted through this area until, in each instance, the tip of the needle was in or near the center of the muscle belly. In the case of the pronator quadratus, the needle was introduced lateral to the radial artery, and passed medially behind the artery and so into the fleshy bulk of the muscle in front of the radius (fig. 3 ) . Precautions were taken to avoid transfixing other muscles and tendons. In each subject, three series of records were made. In the first series, the elbow was kept in the extended, fully supported position on the table top (fig. 2 - a ) . In the second series, the elbow was flexed to a right angle, with the forearm vertical and the arm and elbow supported (fig. 2-8). In the third series, the elbow was flexed to an acute angle while it was still fully supported (fig. 2-y). In each of these three series, records from the two muscles were made during the following movements and held positions : ( a ) slow pronation from the comfortable supine position to the fully prone position, (b) fast pronation through the above range ( 6 subjects only), ( c ) “hold in the fully prone position, ( d ) slow supination through the whole range to full (forced) supination, and (e) fast supination through the above range. Finally, records were made during slow flexion of the elbow in 7 subjects who were sitting upright with the limb hanging freely. Analysis of records. On the basis of earlier experience, we recognized 5 degrees of activity in addition to “no activity,” viz., very slight or negligible, slight, moderate, marked, and very marked. The observations were tabulated and analyzed. OBSERVATIONS Pronation and supination Slow pronation. In all 8 subjects, regardless of the position of the elbow, the pronator quadratus was much more active than the pronator teres. The activity of pronator teres was not affected by the position of the elbow joint in individual subjects although the amount of its activity differed from subject to subject. The activ45 46 JOHN V. BASMAJIAN A N D ANTHONY TRAVILL Fig. 1 Stanley Cox special 6-channel electromyograph. ity of quadratus was generally marked while that in the teres was generally slight. (See fig. 4a.) Fast pronation. Regardless of the position of the elbow joint, in the majority of observations (12 of 16) the activity in the pronator quadratus was very marked while that in the pronator teres was moderate. (See fig. 4b.) In a minority ( 4 of 16 observations) the activity was marked in both muscles. The position of the elbow has slight if any significance in the degree of Fig. 2 Primary postions of limb during three series of tests (see text). Fig. 3 Positioning of needle electrode in pronator quadratus (schematic). 47 ELECTROMYOGRAPHY O F PRONATORS i t;: 48 JOHN V. BASMAJIAN AND ANTHONY TRAVILL Lockhart, Hamilton and Fyfe, '59). Of the North American textbooks, e.g., Gray's Anatomy edited by Goss, ('59), almost all sit squarely on the fence and suggest that both muscles pronate without preference. Only two of them firmly indicate that the pronator quadratus is the main pronator (Hollinshead, '58; Basmajian, '60). A number of authors have likewise expressed the view that the pronator teres displays its greatest activity during midflexion of the elbow (Steindler, '55; Lockhart, '51) or during full extension (Hamilton and Appleton, '56; Hollinshead, '58). However, we were surprised to find that whether the pronating action is carried out swiftly or slowly, the angle of the elbow joint has no bearing on the amount of activity of the pronator teres. During slow supination we find no activity whatsoever in either of the pronatorsFlexion of elbow though some have suggested that the During flexion of the elbow while the deeper layer of the pronator quadratus acts subjects were seated upright, there was as a supinator. De Sousa et al. ('57, '58), negligible or no activity in all but one of using a different approach, have independthe 7 subjects in which this was done (fig. ently arrived at the same conclusion. During fast supination, we find similarly 4c). In this one subject, there was moderate activity in pronator teres at the end of that there is negligible activity in the proflexion which was associated with pain at nators. This is somewhat surprising in that time. This, incidentally, was the only view of earlier work on the electromyooccasion on which pain was experienced graphic activity of the biceps and triceps during flexion and extension of the elbow throughout the entire series. ( Barnett and Harding, '55; Basmajian and DISCUSSION Latif, '57). In those muscles, a sharp Our observations reveal that, although burst of antagonistic activity during fast both pronator quadratus and pronator teres movements has been reported, this activity are active during pronation, the consistent being thought to be the manifestation of a prime pronating muscle is the pronator protective stretch reflex. Flexion of the unloaded forearm does quadratus. This is true irrespective of the position of the forearm in space or the an- not require the participation of the progulation of the elbow joint. We find that nator teres. On the other hand, since we the pronator teres, on the whole, is called were not concerned in this study with pathin as a reinforcing pronator whenever the ological lesions or conditions of loading, we action of pronation has to be carried out are prepared to believe that it may help speedily. We have also found in a parallel during flexion under these special condistudy (to be published) that similar tions. SUMMARY reinforcement occurs during pronation against resistance. But whether the action An electromyographic study (with needle is fast or slow, the activity in the pronator electrodes) of the pronator teres and the quadratus is markedly greater than that in pronator quadratus in a series of volunthe pronator teres. This observation is at teers revealed that, contrary to general variance with the opinions offered in a belief, the quadratus is always the prime number of the recognized textbooks pronator muscle. The teres is the auxiliary (Steindler, '55; Johnston, Davies and which reinforces fast pronation or pronaDavies, '58; Hamilton and AppIeton, '56; tion against resistance, and the amount activity in either the teres or the quadratus of individual subjects. Fully prone ( "h o ld) position. Regardless of the position of the elbow joint, there was always much more activity in the pronator quadratus than in the teres. Generally, the quadratus was markedly active while the teres was slightly active. Slow supination. Regardless of the position of the elbow joint, there was no activity in either muscle except in one subject. (In this one subject there was moderate activity in pronator teres during supination of the extended forearm, but no immediate cause of this could be ascertained. ) Fast supination. Regardless of the position of the elbow joint, the activity in the pronators was negligible in all subjects. There was no burst of reflex activity. ELECTROMYOGRAPHY OF PRONATORS of activity in it is not affected by the position of the elbow. There is no activity in the pronator muscles during supination. The pronator teres is only an insignificant flexor of the elbow. ACKNOWLEDGMENT This work was supported by grants from the National Research Council of Canada and the Rehabilitation Foundation for Poliomyelitics and Orthopedically Disabled (March of Dimes). We deeply appreciate the able technical assistance of Glenn Shine and Patrick Koen and the eagerness of our students to volunteer as subjects. LITERATURE CITED Barnett, C. H., and D. Harding 1955 The activity of antagonist muscles during voluntary movement. Ann. Phys., Med., 2: 290-293. Basmajian, J. V. 1957 Electromyography of two-joint muscles. Anat Rec., 129: 371-380. 1958 A new 6-channel electromyograph for studies on muscle. I. R. E. Trans. on Med. Electronics, PGME-11; 45-47. 1960 Cates’ Primary Anatomy, 4th ed. Williams and Wilkins, Ltd., Baltimore, p. 156. Basmajian, J. V., and A. Latif 1957 Integrated actions and functions of the chief flexors of the - 49 elbow. A detailed electromyographic analysis. J. Bone Joint Surg., 39A: 1106-1118. de Sousa, 0. M., W. R. de Morais, and E. F. Ferraz 1957 Observapoes anatarnicas e eletromiogrAficas sabre o “m. pronator quadratus.” Fol. Clin. Biol., 27: 214-219. de Sousa, 0. M., W. R. de Morais, and E. C. de F. Fenaz 1958 Estudo eletromiogr&fko de alguns mfisculos do antebrapo durante a pronaGao. Rev. Hosp. Clin. 13: 34-54. GQSS, C. M. 1959 (editor) Gray’s Anatomy of the Human Body, 27th ed. Lea & Febiger, Philadelphia, pp. 501, 505. Qamilton, W. J., and A. B. Appleton 1956 In: Textbook of Human Anatomy, by J. D. Boyd, W. E. Le Gros Clark, W. J. Hamilton, J. M. Yoffey, S. Zuckerman and A. B. Appleton. Macmillan & Co. Ltd. London, p. 206. Hollinshead, W. H. 1958 Anatomy for Surgeons. Hoeber-Harper, New York, vol. 3, p. 388. Johnston, T.B., D. V. Davies and F. Davies 1958 Gray‘s Anatomy: Descriptive and Applied, 32nd ed. Longmans, Green and Co., London, New York, Toronto, pp. 496, 632. Lockhart, R. D. 1951 In: Cunningham’s Textbook of Anatomy, 9th ed., ed. by J. C. Brash. Oxford University Press, London, New York, and Toronto, p. 504. Lockhart, R. D., G. F. Hamilton and F. Fyfe 1959 Anatomy of the Human Body. Faber and Faber, Ltd., London, pp. 92, 216. Steindler, A. 1955 Kinesiology of the Human Body. Charles C Thomas, Springfield, Ill., p. 503.