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Electromyography of the pronator muscles in the forearm.

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Electromyography of the Pronator Muscles
in the Forearm
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
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
Finally, records were made during slow
flexion of the elbow in 7 subjects who were
sitting upright with the limb hanging
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.
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
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).
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
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.
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.
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.
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.
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
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.
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Yoffey, S. Zuckerman and A. B. Appleton. Macmillan & Co. Ltd. London, p. 206.
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Johnston, T.B., D. V. Davies and F. Davies 1958
Gray‘s Anatomy: Descriptive and Applied, 32nd
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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
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and Faber, Ltd., London, pp. 92, 216.
Steindler, A. 1955 Kinesiology of the Human
Body. Charles C Thomas, Springfield, Ill., p.
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muscle, pronators, electromyography, forearm
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