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Electromyography of pronators and supinators in great apes.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 87:215-226 (1992)
Electromyography of Pronators and Supinators in Great Apes
RUSSELL H. TUTTLE, JOHN R. HOLLOWED, AND
JOHN V. BASMAJIAN
Department of Anthropology, University of Chicago, Chicago, Illinois
60637 (R.H.T., J.R.H.); Rehabilitation Centre, Chedoke Hospitals,
McMaster University School of Medicine. Hamilton, Ontario. Canada
L8N 3L6 (J.V.B.)
Biceps brachii, Chimpanzee, Gorilla, Orangutan,
KEY WORDS
Positional Behavior, Manipulation
ABSTRACT
We obtained electromyographic recordings from the supinator, biceps brachii, pronator quadratus, and pronator teres muscles of a
chimpanzee and a gorilla and from the supinator, pronator quadratus, and
biceps brachii muscles of an orangutan as they stood and walked quadrupedally on horizontal and inclined surfaces, engaged in suspensory behavior,
reached overhead, and manipulated a variety of foods and artifacts.
In Pan troglodytes and Pangorilla, as in Homo sapiens, the supinator muscle
is the prime supinator, with the biceps brachii muscle serving to augment
speed or force of supination. Primacy of the pronator quadratus muscle over
the pronator teres muscle during pronation is less clear in the African apes
than in humans. Possibly, pongid radial curvature or forelimb elongation or
both factors are related to the somewhat different patterns of activity that we
observed in the pronator muscles of Pan versus those reported for Homo
sapiens.
In Pongo pygmaeus, as in P. troglodytes and P. gorilla, the pronator
quadratus muscle acts as a pronator and the supinator muscle acts to supinate
the hand a t the radioulnar joints. The biceps brachii muscle is active at low
levels as the orangutan supinates its hand with the elbow flexed.
Over the past half century, electromyography has revitalized, indeed revolutionized,
human and other primate functional morphology (Basmajian and De Luca, 1985; Tuttle et al., 1979; Jouffroy, 1989).For instance,
among the revised functional inferences in
human anatomy, premised on EMG studies,
is that the pronator quadratus, not the pronator teres, muscle is the prime pronator of
our hands.
Because the manual rotators-pronator
quadratus, pronator teres, supinator, and
biceps brachii muscles-are grossly similar
to human ones in their bony attachments
(Sonntag, 1924; Howell and Straus, 1961;
Gregory, 1950; Tuttle, personal observations) and because the radioulnar joints of
extant great apes and humans are more
freely movable than those of most other
mammals (Knussman, 1967; Lewis, 1989;
OConnor, 1975; O’Connor and Rarey, 1979),
we might expect them t o act similarly in
@ 1992 WILEY-LISS,INC.
comparable behavioral contexts. However,
the different relative masses of the manual
rotator muscles between apes and humans
(Tuttle, 1969,197071972a,b),combined with
the different proportional lengths and curvature of the upper limb bones (Schultz, 1956;
Erikson, 1963; Hollowed, 1986; Swartz,
1990) and shapes of attachment points for
the rotator muscles (Senut, 1989; Aiello and
Dean, 19901, signal that they may not be
closely comparable (Hollowed, 1986). Accordingly, we recorded, via electromyography (EMG),the supinator and pronator muscles of a common chimpanzee (Pan troglodytes), a western gorilla (Pan gorilla), and a
Sumatran orangutan (Pongo pygmaeus) in
order to determine which muscles were principally and otherwise active during manipulation, quadrupedal positional behavior, and
suspensory activities.
Received October 16,1989; accepted September 3,1991
216
R.H. TUTTLE ET AL.
METHOD
Eleven EMG experiments were conducted
during a 16.5-month span on the right forelimb of a female western gorilla, which was
between 4.5 and 6 years old and weighed
between 34 and 42 kg. Eight EMG recording
sessions were conducted during a 15.5month span on the right forelimb of a captive-born male chimpanzee, which was between 4 and 5.5 years old and weighed
between 17 and 29 kg. Five EMG experiments were performed over a 14-month span
on the right forelimb of a captive-born female
orangutan, which was between 6 and 7.5
years old and weighed 24 and 28 kg.
Indwelling fine-wire bipolar electrodes
were used according to procedures developed
by Tuttle and Basmajian (1974a). A subject
was injected in the hip or left arm muscles
with 13.5-15.0 mgkg body weight of Ketalar
(ketamine hydrochloride)and 0.4 mg of atropine. Karma fine-wire bipolar indwelling
electrodes were implanted in five muscles of
the right forelimb with 26-gauge hypodermic
needles. The electrodes were placed centrally in the bellies of the muscles. Needles
for the pronator quadratus and supinator
muscles were inserted until their tips contacted bone. Before withdrawing them, the
radioulnar joint was rotated to verify electrode placement in these two muscles and in
the pronator teres muscle, which, like the
biceps brachii muscle, is readily located due
to its size and superficial position in the
limb. Rotations of the radioulnar joint and
flexion-extension of the elbow joint served
also to draw the electrodes more deeply into
the muscles.
Five channels of electromyogram, one
channel of reference pulse (Tuttle and Basmajian, 1978a: p.731, and one-channel of
narration were calibrated and recorded on
an Ampex SP 300 8-channel tape recorder.
Concurrently, 4 or 5 EMG channels were
displayed on a Model 564B Tectronix oscilloscope. A Panasonic split-screen television
unit was used to videotape the subject, the
EMG display on the oscilloscope, and the
narration. Behavior and EMG displays are
precisely synchronous on the video tapes
(Tuttle and Basmajian, 1978a,b).
After the recording sessions, pen writer
recordings of EMG activity were made from
the FM tapes. Narration, time, and other
referents were written along the bottoms of
the records. After identifying the most prominent activities of each muscle on the record
of an experiment, the relative magnitudes of
all other EMG action potentials were graded
marked, moderate, slight, negligible, and nil
(Basmajian and De Luca, 1985).
Behaviors that were accompanied by artifact-free EMG potentials on one or more
channels were described on the basis of repeated examinations of the video tapes at
normal and slow speeds with a Panasonic
Tape-a-Vision model NV-3020. We recorded
while the subjects were recovering from anesthesia and thereafter. Unless stated otherwise, the observations narrated below are
from subjects that were well coordinated and
showing no effects of anesthesia.
The subjects could move freely in the 3.6 m
by 3.9 m testing area and could climb on a
trapeze and reach for foods suspended on
strings from the ceiling, attached high on the
walls, and held overhead by an investigator
(Tuttle et al., 1983, Fig. 1;1979; Tuttle and
Basmajian, 1978a,b). The subjects were in
no sense “fettered,” as has been charged by
Larson and Stern (1986). The ribbon cable,
which conveys the EMG potentials to recording equipment, is highly flexible; and, it is
quite easy for the investigator (R.H.T.) to
keep the subjects and himself from getting
tangled in it. Indeed, we used it in Japan
with rapidly running, climbing, and brachiating gibbons without impairing their locomotion, except when the investigators chose
to tug on it in order to encourage them to
climb down from high supports near the
ceiling.
In the chimpanzee, the four forearm rotators were recorded simultaneously during
one experiment; the supinator, biceps
brachii, and pronator teres muscles were
recorded simultaneously during a second experiment; and the supinator and pronator
quadratus muscles were recorded together
during a third experiment. In the gorilla, the
four rotators were recorded together during
one session and all except the pronator
quadratus muscle were recorded during a
second session. Only the pronator quadratus
and biceps brachii muscles were simultaneously recorded in the orangutan.
OBSERVATIONS
Supinator
The supinator muscle was recorded in four
experiments for the chimpanzee, two for the
gorilla, and one for the orangutan. In all
subjects it was primarily responsible for supinating the hand at the radioulnarjoints. In
EMG OF PONGID PRONATORS AND SUPINATORS
217
,
Pt
,
0
1
2
3
4
sec.
Fig. 1. The chimpanzee picks up an M&M candy from the floor: initially he pronates the
hand (sec. 0-2); then (sec. 2-41, he supinates the hand and flexes the elbow, carrying the sweet
to mouth. (Symbols: pq, pronator quadratus muscle; su, supinator muscle; pt, pronator teres
muscle; bb, long head of the biceps brachii muscle)
the chimpanzee, the supinator muscle was
active at variable levels in all suspensory
behavior. It showed phasic EMG activity in
most locomotor behavior in both African
pongid subjects.
In the chimpanzee, supination and flexion
of the elbow during feeding bouts usually
was accompanied by negligible EMG activity
in the supinator muscle, but slight, moder-
ate, and marked EMGs were recorded occasionally (Fig. 1). The level of activity depended on the degree to which the hand was
supinated. Often there was negligible activity as the hand initially left the mouth. Supination while extending the elbow elicited
slight and moderate EMGs. Activity was
negligible when markedly supine hand positions were maintained, and it remained neg-
R.H. TUTTLE ET AL.
218
bl
I
1
1
.
su
bs
I
see.
Fig. 2. The chimpanzee leaps from the floor to grab
the trapeze (sec. 0) and slowly rotates clockwise unimanually beneath the bar (sec. 1-3). Then (sec. 3-81, he flexes
his right elbow acutely and forages overhead with his left
hand. His right hand is prone on the bar; but, there is
intermittent subtle pronation and supination as he
gropes overhead. Finally (sec. %9),he drops to the floor.
(Symbols: bl, long head of the biceps brachii muscle; su,
supinator muscle; bs, short head of the biceps brachii
muscle; pt, pronator teres muscle)
ligible as pronation was subsequently initiated. In all other instances of pronation, the
supinator muscle was silent.
The supinator muscle was active at moderate to marked levels as the chimpanzee
held a large plastic ball against his chest
with the hand in semiprone or slightly supine positions. Although initially moderate,
EMG activity decreased to negligible as the
subject reached up t o the handler with his
hand semiprone. Activity dropped to nil as
he held the handler around the shoulders
and was carried. Holding the investigator
around the neck with his hand semiprone
elicited slight EMG activity in the supinator
muscle.
As the chimpanzee reached overhead for
the trapeze bar or food sill, supinator activity
varied from nil to marked. Standing and
holding the trapeze bar yielded nil activity.
As the subject hoisted himself unimanually
or bimanually on the trapeze and sill, with
the hand in diverse positions, slight-to-moderate and marked EMGs were recorded (Fig.
2). Unimanual and bimanual pendant suspension usually produced negligible and
slight EMGs, but moderate levels were occasionally recorded also. During clockwise rotation about the right hand while hanging
from the trapeze, EMG activity was marked
or moderate. The supinator muscle was silent or active at low levels as the chimpanzee
rotated counterclockwise.
While the subject was still recovering from
EMG OF PONGID PRONATORS AND SUPINATORS
the effects of anesthesia, the supinator muscle was active at moderate and marked levels
during knuckle-walking. Then EMGs decreased to negligible and slight as he became
fully alert. The supinator muscle was commonly active throughout the swing and early
stance phases of knuckle-walking. Usually
the EMGs were phasic during the swing
phase and decreased from mid-swing. The
supinator muscle was occasionally active
just before the hand was released from contact with the substrate. EMG activity was
rarest during mid-stance, and if it occurred
then, it was at low levels.
During knuckle-walking, the chimpanzee
positioned his hands more variably than the
gorilla did. But the levels and pattern of
EMG activity did not change as the chimpanzee knuckle-walked slowly and rapidly on
the floor and as he knuckle-walked up the
ramp. Knuckle-walking down the ramp was
accompanied by negligible and slight activity in the supinator muscle. Further, EMG
occurred immediately before release of the
hand more commonly when he knucklewalked down the ramp than when he knuckle-walked up the ramp or on the floor. When
the quadrupedal subject slid his mid phalanges along the floor, continuous, negligible-toslight EMGs were produced by the supinator
muscle.
The supinator muscle exhibited marked
activity as the chimpanzee swung his hand
up to a platform and climbed onto it. As he
stepped headfirst off the platform or ramp
onto his extended, knuckled forelimb, the
supinator muscle was active at levels ranging from negligible to marked. It usually fell
silent when his knuckles contacted the floor.
Once, however, EMG activity increased as he
markedly supinated his hand upon contact
with the floor. Marked EMGs were recorded
from the right supinator muscle as the subject exited the platform onto his left mid
phalanges while his right palm remained on
the platform. The activity ceased as his right
hand left the platform.
As the seated chimpanzee rose to quadrupedal postures, the supinator muscle was
active at negligible-to-slight levels. When he
rose from prone positions to quadrupedal
stances, the supinator muscle exhibited
marked EMGs.
As the chimpanzee stood quadrupedally
on fisted hands, the supinator muscle produced negligible-to-slight potentials. Knuckle-walking stances were accompanied by
219
negligible EMGs, except once when his forelimb was retracted. On that occasion, EMG
activity was slight in the supinator muscle.
As he sat resting his knuckles or fist on the
floor there was nil, negligible, or occasionally slight EMG activity. EMGs were negligible as he sat with the dorsum of his hand
resting on the floor.
Generally, EMG levels decreased as a resting posture was maintained. But once the
supinator muscle exhibited continuous
slight activity as the seated subject leaned
forward while supporting himself on the
knuckled right hand.
The gorilla’s supinator muscle exhibited
variable levels of EMG activity as she supinated her hand during manipulation. Supination with concurrent elbow flexion or extension and supination with the elbow
sustained in a flexed or extended position
produced EMGs ranging from negligible to
marked. The supinator muscle was inactive
during pronation.
Early in one session, EMGs ranging between slight and marked occurred in the
supinator muscle as the subject stood bipedally and held the trapeze bar unimanually
and bimanually. But, during similar behavior later in the session, EMG activity
dropped to nil. Pulling on the trapeze bar
elicited slight EMG activity. When the bipedal subject held the bar unimanually and
alternately supinated and pronated her
hand, EMGs, ranging from slight to marked,
occurred during supination and nil EMG
accompanied pronation. Clockwise rotation
about the radioulnar joint as the subject
stood bipedally and held the sill was accompanied by marked activity; and, counterclockwise rotation elicited nil activity in the
supinator muscle. On one occasion, the supinator muscle was negligibly active as the
subject stood bipedally and leaned against
the facing wall with her palmed hand as a
brace. Activity remained negligible as she
laterally flexed her trunk to the left and
rotated counterclockwise about her hand.
Activity was marked as she kept her palm
against the wall and returned to a more erect
posture.
The gorilla’s supinator muscle exhibited
EMGs ranging from nil to slight during bimanual suspension on the trapeze. And activity was marked during clockwise rotation
about the right hand while unimanually and
bimanually suspended on the trapeze; it was
nil during counterclockwise rotation. As the
220
R.H. TUTTLE ET AL.
iments for the chimpanzee, two for the gorilla, and three for the orangutan. Each head
was recorded separately once in the chimpanzee and in the orangutan. Only the activity of the biceps brachii muscle during rotatory actions is reported here. Further discussions on the electromyography of the biceps brachii muscle in pongid apes are in
papers by Tuttle and Basmajian (1974) and
Tuttle et al. (1983).
The biceps brachii muscle was relatively
inactive during bouts of supination, especially in the gorilla. Prominent activity was
occasionally recorded in the chimpanzee.
Both heads produced similar activity in the
gorilla and orangutan. In the chimpanzee,
activity of the long head of the biceps brachii
muscle was often less than that of its short
head.
The chimpanzee’s biceps brachii muscle
was active at negligible and slight levels as
the subject supinated his hand while flexing
his elbow (Fig. 1). Negligible to moderate
activity was recorded during supination
with the elbow flexed. Hoisting on the trapeze, while rotating clockwise about the
right hand, was accompanied severally by
slight, moderate and marked EMGs (Fig. 2).
Clockwiserotation about the hand when suspended from the trapeze was accompanied
sometimes by moderate and marked activity; counterclockwise rotation elicited negligible and slight activity in the biceps brachii
muscle. The chimpanzee’selbow was usually
flexed slightly during rotation beneath the
trapeze. His biceps brachii muscle was commonly active during the initial swing phase
of knuckle-walking.
The gorilla’s biceps brachii muscle exhibited nil activity during supination with the
elbow flexed. Supination, concurrent with
elbow flexion, often elicited negligible and
slight EMGs; and, it was occasionally accompanied by nil EMG. The biceps brachii muscle was rarely active during the early swing
phase of knuckle-walking. But during
knuckle-walking, the gorilla exhibited less
radioulnar rotation than the chimpanzee did
and her elbow was less flexed than his was in
all phases of the knuckle-walking stride.
The orangutan’s biceps brachii muscle was
consistently active at slight levels as she
supinated and flexed her elbow; the levels
are similar t o those recorded during flexion
without concurrent supination. The biceps
Biceps brachii
brachii muscle was active a t slight levels
The two heads of the biceps brachii muscle during supination of the flexed elbow. It
were recorded simultaneously in four exper- evinced negligible and slight EMGs during
subject raised her feet to the bar during
bimanual suspension, slight activity occurred.
Rotation counterclockwise while hoisting
elicited nil activity; bimanual hoisting without concurrent rotation produced slight activity.
The supinator muscle was active at negligible and slight levels during the late swing
and early stance phases of knuckle-walking
on the floor and up the ramp and when the
subject slid her knuckles or palm (with interphalangeal joints flexed) across the floor. It
was occasionally active throughout the
swing phase. When she raised her forelimb
from the floor to the platform, activity varied
from slight to marked. Knuckle-walking
down the ramp was accompanied by EMGs
ranging from nil to moderate, with a more
variable pattern of muscle action than occurred while walking up the ramp or across
the floor. EMGs ranging from negligible to
moderate were seen as the subject stepped
headfirst off the platform onto her knuckles.
Nil and negligible activity was recorded in
the gorilla’s supinator muscle during quadrupedal stances on the knuckles or modified
palm and during tripedal knuckled stances
on level surfaces or when facing uphill on the
ramp. Tripedal knuckled stances while facing downhill elicited negligible and slight
EMGs. Nil activity occurred in the supinator
muscle as the subject sat with her fist resting
on the floor.
When the seated subject rose to quadrupedal stances, her supinator muscle exhibited negligible activity. On one occasion the
groggy subject attempted to rise to a quadrupedal posture by repeatedly pushing against
the floor with concurrent pronation of the
hand. EMG activity ranged between negligible and slight during the pushing and pronation and between slight and marked during
the recovery stroke with supination before
the next push.
In the orangutan, the supinator muscle
was silent or negligibly active during quadrupedal stances and locomotion. Commonly,
she slid her fist or modified palm instead of
employig a true swing phase. When she did
swing the fist free of the floor, movement
occurred chiefly at the shoulder joint, with
distal forelimbjoints held more or less stiffly
in the positions of the preceding stance
phase.
EMG OF PONGID PRONATORS AND SUPINATORS
22 1
While standing quadrupedally on the knuckles, EMG activity was usually nil, but some
negligible activity was recorded in the pronator quadratus muscle. Negligible activity ocPronator quadratus
curred as the subject stood tripedally on his
The pronator quadratus muscle was re- knuckles or quadrupedally on his fists. Sitcorded in two experiments for the chimpan- ting with the knuckles resting on the floor
zee, one for the gorilla, and two for the elicited nil activity.
In the gorilla, pronation of the forearm as
orangutan. It was active at variable levels in
pronation of the free hand and during sus- it rested on the floor was accompanied by
pensory behaviors. It was also active during marked activity in the pronator quadratus
at least some of the stance phase of quadru- muscle. Activity decreased as the pronated
position was maintained; it ceased within 30
pedal locomotion in all subjects.
As the chimpanzee pronated and extended seconds.
Activity was moderate as the gorilla
his forearm while feeding off the floor or
while taking food from the investigator’s reached overhead for the trapeze with her
hand, EMGs ranging from negligible to mod- hand prone. It dropped t o slight levels as she
erate occurred in the pronator quadratus grabbed the trapeze and held it bimanually
muscle (Fig. 1). Activity was nil during pro- with her hands prone and subsequently as
nation from a markedly supinated to a semi- she raised her feet to the bar.
During slow knuckle-walking, the gorilla’s
prone position. Negligible and slight activity
occurred as he sat holding his foot with the pronator quadratus muscle was usually active at negligible and slight levels, with occahand prone.
EMG activity was initially negligible, but sional bursts of marked activity, during mid
increased to marked as the chimpanzee and late stance and early swing phases of the
reached up to the handler with the hand stride. The pronator quadratus muscle was
semiprone. Activity dropped to nil as he held active more often at the onset of swing phase
the handler with the hand semiprone. in the gorilla than in the chimpanzee. When
Reaching overhead for the trapeze and grip- the subject stepped onto the stage, high acping the bar with the hand prone elicited tivity was occasionally recorded just before
negligible, slight, and occasionally moderate knuckle contact. Sliding the knuckles off the
activity. It dropped to nil as the bipedal ramp onto the floor elicited nil activity. Negsubject held the trapeze with the hand ligible and slight activity occurred as the
gorilla walked quadrupedally while sliding
prone.
No data were recorded for the pronator her fist; but activity was nil as she slid her
quadratus muscle during suspensory behav- hand in a modified palmigrade posture.
ior by the chimpanzee because he did not Climbing onto the stage with the hand in a
hang from the trapeze while we were moni- modified palmigrade position was accompanied by slight and moderate EMG activity.
toring it.
Activity was nil in the pronator quadratus
Nil, and less often, negligible, levels of
EMG were recorded in the pronator quad- muscle during knuckled quadrupedal stances,
ratus muscle during the load-bearing phase but it varied from nil to slight when her hand
of knuckle-walking as the chimpanzee was in a modified palmigrade posture.
walked at various speeds on a level surface, Standing tripedally on the right knuckles
walked up or down the ramp, or slid his while facing down the ramp elicited nil activknuckles along the floor during quadrupedal ity. Early in the experiment, as the groggy
progression. Occasional slight activity oc- subject tried to rise from sitting to a
curred early in one session as the subject quardupedal stance, EMG activity varied
knuckle-walked. Highly variable levels of from negligible to marked; the activity was
activity, ranging from nil to marked, were highest as she pushed on the floor and
recorded as he stepped off the stage onto his slightly pronated her forearm several times
right knuckles. While stepping off the stage while attempting t o rise. The EMG levels
onto his left knuckles, activity in the right dropped as she relaxed.
In the orangutan, pronating the free hand
pronator quadratus muscle was negligible; it
dropped to nil as the right hand neared the was accompanied by EMGs ranging from
negligible to marked in the pronator quadrafloor.
Occasionally nil, but usually negligible, tus muscle. Activity was usually greater
activity occurred as the chimpanzee rose when the subject pronated her hand from a
from a sitting to a quadrupedal posture. supine to a prone position than when her
the early swing phase of fist-walking and
crutch-walking.
222
R.H. TUTTLE ET AL
hand was only slightly rotated. But occasionally full pronation elicited only negligible
activity.
Pronation was accompanied by similar activity levels whether the elbow was flexed or
extended. Pronating the fist as it rested on
the floor elicited negligible to slight activity
when the forearm was also on the floor and
marked activity when the forearm was off
the floor. While the orangutan picked food
off the floor, EMG activity was negligible in
the pronator quadratus muscle as the hand
approached the floor, marked as the food
was grasped, and nil and the forearm was
flexed and supinated. While lying supine
with the right forelimb abducted, the pronator quadratus muscle was active in maintaining hand position; EMG activity was nil
when the hand was supine, negligible when
it was semiprone, and slight when it was
prone. Negligible and slight levels occurred
as she pushed a heavy box across the floor
with the right palm while walking tripedally
and while sitting and pushing the box with
both palms. Once, the pronator quadratus
muscle evinced a short burst of negligible
activity as she supinated her free hand. Negligible and slight EMGs occurred as she supinated her hand and hit a large rubber ball
with its dorsum.
EMGs ranging from negligible to moderate occurred as the orangutan reached overhead with her hand semiprone. There was
slight activity as she pulled weakly on the
trapeze bar with her hand semiprone. When
she reached into a food tray above the trapeze, activity varied from negligible to
marked; but the degree of pronation could
not be seen on the video tape. While the
subject stood bipedally and rotated the bar of
the trapeze overhead counterclockwise, activity was slight as her hand rotated from a
supine to a seimiprone position. Then EMGs
increased from moderate to marked as her
hand continued from a semiprone to a prone
position.
Quiescent pendant suspension unimanually, bimanually, and with one or both feet on
the bar usually elicited nil activity in the
pronator quadratus muscle, but rare negligible activity also was recorded. Activity was
slight during suspension with the hyperprone right hand and both feet on the bar.
Counterclockwise rotation about the right
hand during unimanual suspension produced slight activity. Activity was nil during
clockwise rotation. The pronator quadratus
muscle was silent as the subject swung uni-
manually and bimanually on the trapeze.
Bimanual hoisting elicited nil, negligible, or
occasionally slight levels of activity. Negligible and slight activity was recorded as she
rotated counterclockwise about the right
hand while hoisting herself bimanually on
the trapeze.
The pronator quadratus muscle exhibited
less consistently patterned activity during
quadrupedal progression in the orangutan
than in the African apes. EMG activity was
usually negligible, but occasionally it reached
moderate levels while she fist-walked. Activity was usually constant throughout the
stride, but often it dropped during the swing
phase. During slow fist-walking, activity occurred during the early and mid-stance
phases, a s it does during chimpanzee knuckle-walking. Negligible and slight EMGs were
elicited a s the orangutan shuffled her fists
across the floor. When stepping off the stage
or ramp onto the right fist, activity varied
from negligible to marked.
Slight and moderate activity was recorded
during the load-bearing phase of quadrupedal walking with the hands in a modified
palmigrade posture. On one occasion, the
pronator quadratus muscle was active during the late swing phase. The orangutan
frequently shuffled or slid her palms along
the floor. This elicited negligible and slight
EMGs throughout the stride. While shuffling down the ramp, EMG activity was continuous at negligible levels.
Crutch-walking, with fisted hands, produced slight activity during the load-bearing
phase of the stride. Modified palmigrade
crutch-walking yielded negligible activity
throughout the stride.
On one occasion, the orangutan lowered
herself from the trapeze onto her right
knuckles with the elbow extended; negligible
EMG was evinced by the pronator quadratus
muscle.
As the orangutan rose from sitting to quadrupedal stances, negligible EMG was elicited
in the pronator quadratus muscle. Nil and
negligible activity was exhibited during quiescent quadrupedal stances on fisted hands;
nil activity occurred during modified palmigrade quadrupedal stances. Standing tripedally on the fist yielded nil activity, but
modified palmigrade tripedal stances elicited nil to slight levels of activity. Negligible
levels were usually recorded while the subject sat and rested the prone fist or palm on
the floor, though the EMGs occasionally
dropped to nil or rose to slight.
EMG OF PONGID PRONATORS AND SUPINATORS
Pronator teres
The pronator teres muscle was recorded in
two experiments each for the chimpanzee
and the gorilla. In the chimpanzee it was
active during the same behaviors that the
pronator teres muscle was. In the gorilla, the
pronator teres muscle acted less frequently
than the pronator quadratus muscle. It appeared to augment the pronator quadratus
muscle during some behaviors.
In the pronator teres muscle of the chimpanzee, activity increased from negligible to
marked levels as he reached up to the handler with his hand semiprone. Then activity
decreased to moderate levels as he held the
handler with the semiprone hand. There was
no activity as he held a large ball against his
chest with the hand semiprone or slightly
supine.
Reaching overhead for the trapeze with
the hand prone elicited negligible and slight
activity in the chimpanzee’s pronator teres
muscle. Hoisting unimanually on the trapeze, with the hand prone, and bimanual
hoisting, with a semiprone or prone hand,
yielded EMGs ranging from slight to marked
(Fig. 2). But unimanual and bimanual hoisting on the sill, with the hand prone, was
accompanied by negligible activity. Quiescent unimanual pendant suspension on the
trapeze with the hand prone also elicited
negligible activity. Hanging bimanually recruited negligible activity when the hand
was semiprone and negligible and slight activity when the hand was prone. Activity was
initially negligible when the chimpanzee unimanually rotated clockwise beneath the trapeze from an initially prone manual position
(Fig. 2). But occasionallythere were bursts of
moderate and marked activity at the end of
the rotation when the pronator teres muscle
apparently acted as a brake.
Early in sessions, the pronator teres muscle was active at levels ranging from slight to
marked as the chimpanzee knuckle-walked.
Later, activity decreased to negligible and
slight levels. The pronator teres muscle was
always active in early and midstance. Activity occasionally began just before knuckle
contact and continued until release. Activity
was uniform as the subject walked up and
down the ramp. Levels of activity remained
negligible and slight during fast knucklewalking on a level surface, but during the
late swing phase it was more common than
during slower knuckle-walking. Sliding the
knuckles along the floor while walking for-
223
wards or backwards elicited negligible to
slight activity throughout the stride. Stepping off the ramp or stage onto the right
knuckles was accompanied by EMGs ranging from negligible to moderate, which commenced as the elbow was extended and decreased as a quiescent stance was assumed.
Standing quadrupedally on his knuckles
yielded negligible activity in the chimpanzees’spronator teres muscle; and fisted quadrupedal stances elicited nil activity. Negligible activity occurred as the sitting subject
rested his knuckled semiprone hand on the
floor; the EMG occasionally rose to slight
when his hand rested in a prone position.
Marked activity was recorded in the gorilla’s pronator teres muscle as she pronated
her hand while leaning on her forearm with
the elbow flexed; activity dropped to nil approximately 45 seconds after she pronated
her hand. Pronation with the elbow extended
was accompanied by negligible and slight
activity. Slight EMG levels occurred during
concurrent pronation and elbow flexion.
Negligible activity was recorded once during
concurrent supination and elbow flexion. Activity was nil during all other instances of
supination with concurrent elbow flexion
and extension and when the elbow was
maintained in a variety of positions. One
instance of extending the elbow with the
hand prone produced negligible activity in
the gorilla’s pronator teres muscle and a
shorter burst of negligible activity was recorded in it during elbow extension with the
hand semiprone. Holding the trapeze while
bipedal elicited negligible and slight activity.
Alternately supinating and pronating the
hand in order to rattle the trapeze produced
nil activity during supination and EMGs
from slight to marked during pronation.
As the gorilla rotated counterclockwise
about her right hand while hanging bimanually, and when she hoisted herself bimanually, marked activity occurred in the pronator teres muscle.
Knuckle-walking elicited slight activity in
the gorilla’s pronator teres muscle early in
recording sessions; but negligible activity
predominated as she recovered from anesthesia. Activity was highest during the
stance phase and occasionally early swing
phase. Whereas supination was the norm at
hand release in the more variable chimpanzee knuckle-walking pattern, the knucklewalking gorilla habitually pronated her
hand at release. Walking quadrupedally
while sliding the knuckles or fists on the
224
R.H. TUTTLE ET AL.
forearm. During supination in the chimpanzee, the biceps brachii muscle was only recruited when the supinator muscle was
prominently active. The biceps brachii muscle was active at lower levels than the supinator muscle, except when he revolved while
hanging from the trapeze; during clockwise
rotation about the right hand, moderate and
marked EMG potentials were recorded in
both muscles. But the biceps brachii muscle
was probably acting to maintain the slight
elbow flexion that was common during his
suspensory behavior on the trapeze. This
inference is supported by the fact that during
the counterclockwise rotation, which immediately followed the clockwise rotation, the
supinator muscle was silent, while the biceps brachii muscle remained active at negligible and slight levels.
At knuckle release during quadrupedal
locomotion,the biceps brachii and supinator
muscles often fired synchronously. In the
gorilla, only the supinator muscle was recruited to supinate the forearm at the flexed
elbow. Usually the biceps brachii muscle was
active at negligible and slight levels during
supination with concurrent elbow flexion;
but occasionally it was inactive. The biceps
brachii muscle was sometimes silent during
instances of supinator activity at knuckle
release, possibly because of the quite extended position of the gorilla elbow during
knuckle-walking.
The pronator and supinator muscles acted
alternately in the African apes as the subjects pronated and supinated their forearms
during manipulation (Fig. 1) and suspensory
behavior (Fig. 2). Synchronous antagonistic
activity during rotation was rarely seen between the pronator teres and supinator muscles in the chimpanzee (Fig. 2). This never
occurred between the pronator quadratus
and supinator muscles.
In the chimpanzee, the pronator teres
muscle was active as a brake at the end of
Simultaneity and discreteness
several bouts of supination on the trapeze. In
The pronators were usually simultane- one instance, his pronator quadratus muscle
ously active in the chimpanzee and gorilla. did not act initially during pronation of the
In both African apes, pronator quadratus forearm from a markedly supinated position;
activity was relatively higher than that of the recoil of the supinator muscle may have
the pronator teres muscle during pronation been sufficient t o initiate pronation. His prowith the elbow extended (Fig. 1).The prona- nator teres and supinator muscles were oftor quadratus muscle appeared to be the ten simultaneously active during hoisting
primary pronator in the gorilla; the relation- behaviors. As he held the investigator
ship between the two muscles is unclear for around the neck with his hand semiprone,
the chimpanzee.
the supinator muscle evinced slight EMGs,
The biceps brachii muscle was secondary the pronator teres muscle produced moderto the supinator muscle as a rotator of the ate EMGs, and the pronator quadratus mus-
floor elicited marked activity in the gorilla’s
pronator teres muscle early, and slight activity later, in test sessions. Knuckle-walking
up and down the ramp recruited negligible
EMG activity in the pronator teres muscle.
Activity during the stride showed less periodicity when she walked down the ramp
than when she walked up the ramp or on a
level surface. Stepping off the stage was
accompanied by negligible and slight activity which often decreased when her knuckles
contacted the floor.
When the gorilla walked with her hands in
a modified palmigrade posture, EMGs rangingfrom negligibleto marked occurred in the
pronator teres muscle during stance phase.
Activity was marked as she climbed onto the
stage with her hand in a modified palmigrade posture.
Nil and negligible EMGs were recorded as
the subject stood quadrupedally on her
knuckles or fists; but activity rose to negligible and slight levels when she used a modified palmigrade stance. Tripedal stances on
the knuckles elicited nil and negligible activity in the pronator teres muscle
Activity was negligible as the subject rose
from a sitting to a quadrupedal posture with
her hand supinated slightly. On one occasion
the groggy subject rose from a sitting position to a quadrupedal stance by pushing and
concurrently pronating the hand several
times. Marked activity occurred as she
pushed and pronated; activity was nil as she
relaxed and supinated between pushes.
The pronator teres muscle was silent as
the gorilla stood bipedally facing a wall and
rested her right palm against it. Activity was
marked as she then leaned to her left and
rotated counterclockwise about the right
hand. Activity dropped to nil as she ceased to
flex her body laterally; it remained nil as she
stood erect and rotated clockwise about the
right hand.
EMG OF PONGID PRONATORS AND SUPlNATORS
cle was silent. When he held a large ball
against his chest with the hand semiprone or
slightly supinated, moderate and marked
EMG activity occurred in the supinator muscle and the pronator teres muscle was silent.
The pronators usually alternated with the
supinator muscle during quadrupedal progression by the African apes, though synchronous activity was often seen in these
muscles as the subjects shuffled or slid their
knuckles across the floor.
Insufficient data were recorded on the activity of the pronators as the biceps brachii
muscle acted during elbow flexion without
concurrent supination. Elbow flexion with
maintenance of a prone hand position was
infrequent in all subjects. In the orangutan,
the pronator quadratus muscle was not recruited to maintain a prone hand position
during hoisting. No pattern could be discerned in the chimpanzee or the gorilla during hoisting behavior (Fig. 2).
DISCUSSION
Comparison with humans
The electromyographyof the forearm rotators in humans has been summarized by
Basmajian and De Luca (1985)and MacConnail1 and Basmajian (1969).In humans, as in
African apes, the biceps brachii muscle is
subordinate to the supinator muscle in various supinatory actions.
The pronator quadratus muscle is the primary pronator in humans; but its predominance over the pronator teres muscle is less
than that of the supinator muscle over the
biceps brachii muscle. This relationship may
hold also in the African apes. But the smaller
difference in the activity levels of the pronator muscles and difficulties in obtaining frequent and consistent movements in the apes
leaves this unclear.
Antagonistic behavior, which would be expected at the beginning of rotation and in a
braking capacity at the end of rotation (MacConnaill and Basmajian, 1969),was not seen
in humans. Per contra, antagonistic behavior was occasionally evinced between the
supinator and pronator teres muscles of the
chimpanzee.
Future studies
Having documented basic action patterns
of the pronator and supinator muscles in a
limited arena of experimental challenges, we
are left with questions about their mechanical roles in relation to the shapes and relative lengths of long bones in the forelimbs of
225
natural apes, modern humans, and prehistoric Hominidae. Inferences from Swartz’s
(1990) thoroughgoing study on forelimb mechanics in suspensory anthropoid primates
are suggestive here.
Swartz (1990) found that although differences in muscle mass development as determined by dry weight (Tuttle, 1969,1972a,b),
were correlated with differences in radial
mediolateral curvature between highly suspensory anthropoid primates (gibbons and
spider monkeys) and more quadrupedal
monkeys, this correlation could not explain
either the allometry of curvature or intertaxonal differences in curvature among them.
In order to pinpoint the relationships of specific radioulnar rotator muscles to radial
curvature (and the effects of forelimb elongation), we need concurrent strain gauge measurements on the radius and EMG recordings of the supinator and pronator muscles
as subjects engage in a full spectrum of
stationary and vigorous quadrupedal, suspensory, and manipulatory behaviors. The
preliminary information that we have detailed herein should facilitate the construction of productive experimental protocols.
We also recommend that the hypothesis of
Swartz (1990) that the supinator muscle is
prominently active during hylobatid brachiation be tested in vivo.
These studies should allow us t o interpret
radial curvature in Neandertals (Trinkaus,
1983) and other fossil hominoids with
greater precision and bounded imagination.
ACKNOWLEDGMENTS
This investigation was supported mainly
by NSF grants GS-3209, SOC75-02478, and
BNS 8540290 and by a Public Health Service
research career development award (l-KO4GM16347-01)from the National Institutes of
Health. It was supported also in part by NIH
grant RR-00165 from the Division of Research Resources to the Yerkes Regional
Primate Research Center, which is fully accredited by the American Association of Laboratory Animal Care. We are especially
grateful for the assistance of J. Malone, E.
Regenos, J. Perry, Dr. G.H. Bourne, Dr. F.A.
King, R. Pollard, S. Lee, R. Mathis, J. Roberts, Dr. M. Keeling, Dr. M. Vitti, J. Hudson,
K. Barnes, and L. Doan.
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