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The Function of the teres major muscleAn electromyographic study.

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The Function of the Teres Major Muscle:
An Electromyographic Study '
H. L. BROOME2 AND J. V. BASMAJIAN
Regional Rehabilitation Research and Training Center, Emory University.
and Georgia Mental Health Institute Atlanta, Georgia 30306
ABSTRACT
Electromyographic activity of the teres major and latissimus
dorsi muscles using indwelling bipolar fine-wire electrodes was recorded during
motion of the arm and shoulder without resistance, against resistance, and during static resisted activity. The teres major is active during static motion and
during motion against resistance with medial rotation, adduction, and extension
of the arm. It is not active during motion without resistance, although latissimus
dorsi usually is.
The classic article in the literature on
the kinesiology of the shoulder region is
that of Inman, Saunders and Abbott ('44).
Their findings have in general withstood
the test of time and few of their conclusions have been contradicted by subsequent
investigators.
One point of controversy has been the
function of the teres major muscle which
Inman et al. ('44) reported never showed
activity during motion, having a purely
static function. But Hermann ('60),
Kamon ('65), and DeSousa et al. ('69),
all using surface electrodes, denied this,
reporting that teres major was indeed
active during active motion of the arm.
The present study was undertaken to
clarify the disagreement because of the
obvious importance of this large muscle.
The closely related latissimus dorsi was
studied simultaneously as a reference.
MATERIAL AND METHODS
The teres major muscle of ten normal
adult subjects, using their dominant arm
could usually be easily visualized and
palpated by having the subject adduct and
internally rotate his arm against a static
resistance. In the majority of subjects, the
latissimus dorsi muscle was also easily
palpable. Bipolar fine-wire (75 p ) Karma
electrodes were inserted into the mass of
the teres major 3 cm lateral and 3 cm
superior to the inferior angle of the
scapula; and into the latissimus dorsi
ANAT. REC.,170: 309-310.
muscle 4 cm inferior to the inferior angle
of the scapula. Construction and insertion
of these electrodes have been described
elsewhere (Basmajian and Stecko, '62).
Recordings were made on a four-channel
Thermionic FM tape recorder and viewed
on a four-channel Tektronix storage
oscilloscope.
Subjects were directed through a series
of motions of the shoulder and arm: ( a )
standing at rest with the arms hanging at
the side, ( b ) medial rotation, (c) lateral
rotation, ( d ) abduction, ( e ) adduction,
( f ) flexion, and ( g ) extension. These were
first done without resistance and then
against a resistance force that either allowed or prevented completion of the arc
of the motion.
One channel recorded teres major activity while the second channel recorded
latissimus dorsi activity. Good recordings
were obtained from all ten teres majors
and in seven latissimus dorsi muscles.
RESULTS
The teres major had no electrical activity in motions without resistance. But
against active resistance, it consistently
showed electrical activity during medial
rotation, adduction, and extension in both
Received Oct. 19, '70. Accepted Nov. 24, '70.
1 Supported by grant 16-P-56808/4-07, Social and
Rehabilitation Services, Department of Health, Education and Welfare, Washington, D. C.
2 Resident in Orthopedic Surgery, Georgia Baptjst
Hospital and Scottish Rite Hospital, Atlanta, Georgia.
309
310
H. L. BROOME AND J. V. BASMAJIAN
the static and the dynamic exercises. The
latissimus dorsi had similar activity during
both static tension and resisted motion;
without resistance, in five of the seven acceptable subjects, latissimus dorsi had
activity during medial rotation, adduction,
and extension.
DISCUSSION
The more precise and sensitive techniques used in this study appear to resolve
the controversy over the functions of teres
major. The key to the solution seems to
be whether a movement or an attempted
movement is resisted. If it is resisted, teres
major is always active. If added resistance
is lacking, free movement of the shoulder
joint in all its directions does not recruit
the teres major although it usually recruits
its close relation, latissimus dorsi.
ACKNOWLEDGMENTS
This study was performed with the close
cooperation of Mrs. Eleanor Regenos, Mr.
Glenn Shine, and Mrs. Gail Super, to whom
we are grateful.
LITERATURE CITED
Basmajian, J. V., and G. A. Stecko 1962 A new
biuolar electrode for electromvonraphhv.
- - - - J.
. APP~.
-Piysiol., 17: 849.
DeSousa, 0. M., F. Berzin and A. C. Berardi
1969 . Analise. electromiogrPfica do m. teres
major. “0. Hospital.” (Univ. of Sao Paulo,
Brazil) Nov. 1969,76: 5, 241-247.
Hermann, G. W. 1962 An electromyographic
study of selected muscles involved in the shotput. Res. Quart., 33: 1-9.
Inman, V. T., J. B. deC. M. Saunders and L. C.
Abbott 1944 Observations on the function of
the shoulder joint. J. Bone and Joint Surgery,
26: 1-30.
Kamon, E. 1966 Electromyography of static
and dynamic postures of the body supported on
the arms. J. Appl. Physiol., 21: 1611-1618.
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