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Electromyography of pongid shoulder muscles. III. Quadrupedal positional behavior

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Electrotnyography of Pongid Shoulder Muscles
Ill. QUADRUPEDAL POSITIONAL BEHAVIOR
'
RUSSELL H. TUTTLE A N D JOHN V. BASMAJIAN
Department of Anthropology and Committee on Evolutionary Biology, The University of
Chicago, Chicago, Illinois fiO6.37 and McMaster University and Rehabilitation Centre,
Chedoke Hospitals, Hamilton, Ontario, Canada L8N 3Lfi
-
K E Y WORDS Apes Electromyography . Shoulder muscles
Positional behavior . Knuckle-walking . Quadrupedalism
.
ABSTRACT
Electromyographic (EMG) recordings were taken from 14
shoulder muscles (or major parts of them) in a gorilla, a chimpanzee and an
orangutan as they stood quadrupedally and tripedally, descended from elevated
substrates, crutch-walked, and progressed quadrupedally on inclined and level
substrates.
In the African apes, low potentials commonly (but not always) occurred in
the sternocostal pectoralis major, anterior deltoid, supraspinatus and subscapularis muscles during quadrupedal stance. The quadrupedal orangutan always exhibited low potentials in the pectoralis major muscle and EMG activity
commonly occurred in her supraspinatus and subscapularis muscles. Quiescent
tripedal stances were not accompanied by striking changes in EMG patterns
from those which characterized quadrupedal stances. Per contra, eccentric
loadings of the forelimb during descents from elevated substrates generally recruited notable EMG activity in the deltoid, supraspinatus and, to a lesser extent, infraspinatus muscles of the three pongid apes. The pectoralis major and
caudal serratus anterior muscles were much more active in Pongo and Pun during these descents.
Supportive segments of quadrupedal locomotive cycles were generally accompanied by EMG activity in the pectoralis major, intermediate and posterior
deltoid and supraspinatus muscles. The intermediate and posterior deltoid muscles were characteristically active during pre-release of the hand and early
swing phase. The cranial trapezius and supraspinatus muscles also may act
during early swing phase.
We conclude that the pectoralis major and perhaps the supraspinatus and
subscapularis might serve regularly as postural muscles during static terrestrial quadrupedalism in pongid apes. The lack of dramatic differences between the EMG patterns exhibited during fist-walking versus knuckle-walking
indicates that an evolutionary transformation from a shoulder complex like
that of Pongo to ones like Pun or vice versa need not entail major changes in
myological features.
The main purpose of this report is to present
the first description of electromyographic
(EMG) activities of the shoulder muscles in
pongid apes during spontaneous quadrupedal
positional behavior. In other publications
(Tuttle and Basmajian7 '77, '78) we presented
EMG information about the same muscles as
AM. J. PHYS. ANTHROP. (1978) 49: 57-70.
the subjects raised their arms and engaged in
suspensory behavior and suggested how this
might relate to several current problems on
scapular shape and hominoid phylogeny.
Herein we will focus on mechanisms of pongid
Parts of this paper were read at the AAPA meeting in Toronto,
Canada, April. 1978.
57
Caudal
serratus
anterior
Cranial
trapezius
1
Teres major
c
0
G
c
0
G
c
0
1
1
1
1
2
1
1
2
G
0
1
0
0
0
0
0
0
0
0
0
0
0
0
c
G
1
2
0; +
O;l+l
;+t+;i~~
0
0
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-
0
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0
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-
0
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0-
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+
M
-
0
0
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0;
0;
+
0
0;
0
+
0
0
0
0
0
0
0
0; +
0
0
0
0
S
O;I+l
-
0
-
0
0
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-
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l i i i l
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0
0;
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0;i ;
0;
-
0
0
0
0
0
0
0
0 ;+
0
0
0
M
Swing phase
Quadrupedal walking and lrunningl
Stance phase
t ;
+
S
+;++
++
-
walking
Crutch
+,
0
0
-
0
0
0
0
-
0
-
0
0 ;7
0
[++I
-
t;t+
0
0; + ; I + + I
Descent onto
hand
-
0; t
0
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+
0
0
0
+
0;
G
0
3
0; +
stance
+
c
0
c
2
Quiet
tripedal
0;
1
G
2
Quiet
quadrupedal
ntance
2
2
Subject
N
Vertebrocostal
latissimus
dorsi
Iliac
latissirnus
dorsi
Sterno,costal
pectoralis
major
Muscle
TABLE 1
Activities of pongid shoulder musrles during quadrupedal positional behavior (symbols: N , number of 60-120 rninute experiments; G, gorilla;
C, chimpanzee; 0, orangutan; -, no d a t a ; 0,silent; +, low EMG; +
moderate EMG; + + +, high EMG; S, sluw pace; M, moderate
pace; R, rapid pace). I1 indicate relatively rare occurrences or mainly while the subject w a s groggy.
-
0
I+ + I
0:+;
-
0 ;+
-
0
0
0
0
-
0
0
0
0 ;t
0
0
0
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c
2z
tr
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2
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EMG OF PONGID SHOULDER MIJSCLES AND QUADRUPEDALISM
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59
60
RUSSELL H. TUTTLE AND JOHN V. BASMAJIAN
quhdrupedalism and evolutionary problems of
knuckle-walking. The muscles or major parts
thereof are listed in table 1.
SUBJECTS AND METHODS
The subjects in this study were a 6%-to 7%year-old female Sumatran orangutan (Pongo
pygmaeus); a 5?h- to 6lh-year-old female lowland gorilla (Pan gorilla); and a 4%- to 5%year-old male chimpanzee (Pun troglodytes).
Indwelling fine-wire bipolar electrodes
(Basmajian, '74; pp. 35-39) were used according to procedures which have been described
in previous papers (Tuttle and Basmajian,
'74a,b). The subjects could move freely in the
testing area. They had opportunity to stand
tripedally and quadrupedally on level and inclined surfaces (figs. l a , 2a,b,d), to eccentrically load the forelimb during descents
from a ramp (fig. lb) and platform, and to
walk quadrupedally a t various speeds on the
ramp and floor (figs. lc,d, 2c). We induced
bouts of locomotion up and down the ramp by
placing M & M candies alternately a t its apex
and near its base. Quadrupedal behavior generally commenced during the initial 20 minutes after arrival in the testing area and was
exhibited intermittently throughout the recording period. The 17.8" inclined ramp was
244 cm long, 76 cm wide and 51 cm high a t the
apex. The platform was 91 cm x 76 cm x 51 cm.
RESULTS
The number of recording sessions which
provided useful data on each muscle in the
three pongid apes and general levels of activity during quiescent quadrupedal and tripedal
stances, descents from elevated substrates
with the tested forelimb eccentrically loaded,
crutch-walking, and quadrupedal locomotion
are listed in table 1. Hereinbelow we will discuss the activities of certain muscles and compare results obtained from the three subjects
especially insofar as they might reveal basic
similarities and differences between the habitual knuckle-walkers (gorilla and chimpanzee) and the orangutan. Unless otherwise
mentioned all descriptions are based on data
from fully alert subjects.
Quadrupedal stance
When the gorilla stood quadrupedally, she
habitually extended her elbow so that the arm
and forearm were virtually aligned. Although
the dorsum of the knuckled hand faced directly anteriorly, t h e ulnar olecranon process
was oriented more laterad than posteriorly (as
in figs. lb,c). The shoulders appeared to be
hunched forward somewhat. The chief contact
points with the substrate were the dorsal surfaces of the middle segments of digits 11-IV.
The wrist was slightly volarflexed and adducted, probably loading digits I1 and I11 more
than digit IV. She very rarely stood with a
supportive hand fisted.
During quadrupedal stance, the chimpanzee
exhibited a greater variety of forelimb postures than the gorilla did. The dorsal surfaces
of his knuckled hands faced laterad, anterolaterad, or anteriorly. The olecranon process
was posterior when the dorsum of the hand
faced laterad. But, as in gorilla, it was laterad
when the dorsum of the hand faced anteriorly.
Often weight was borne primarily on digits 111
and IV while digit I1 was rather widely
abducted and flexed so that i t only lightly
touched the substrate. The wrist was slightly
volarflexed and adducted. The elbow joint
commonly exhibited slight flexure. The chimpanzee's shoulders appeared to jut anteriorly
somewhat less than the gorilla's did. The
chimpanzee commonly stood with one or both
hands fisted, especially when he was groggy or
immediately following a bout of rapid progression in which a fisted hand was used during
the stance phase of the final locomotive cycle.
The orangutan exhibited the greatest variety of forelimb postures during quadrupedal
stance. Fisted hands, with the dorsum facing
anteriorly, obliquely or laterad and the ulnar
olecranon process concordantly oriented as described hereinabove for the chimpanzee, were
most commonly employed for static support.
But she also occasionally placed her hands
palmigrade (Tuttle, '671, in a knuckled posture (fig. 2b), or with only the middle fingertips touching the floor. The latter two postures were employed as she stood beneath a
desired object and very slowly rose to a bipedal
posture (fig. 2d) and as she returned from
bipedal foraging to a more fully quadrupedal
stance. Sometimes the arm and forearm were
well aligned. At other times the elbow exhibited flexure during various fisted, palmigrade
and knuckled stances.
In the gorilla and chimpanzee, none of the
shoulder muscles always produced EMG potentials during quadrupedal stance. However,
low activity commonly appeared in their sternocostal pectoralis major, anterior deltoid, supraspinatus, and subscapularis muscles during quadrupedal stance. Several muscles, in-
EMG OF PONGID SHOULDER MUSCLES AND QUADRUPEDALISM
61
Fig. 1 Gorilla female a, standing tripedally on ramp while scratching t h e dorsum of her neck with the left hand; b,
eccentrically loading t h e extended right forelimb during a descent from the ramp; and c,d, knuckle-walking, Note (a-c)
that the olecranon process of the ulna faces laterad when the dorsum of the knuckled hand is oriented anteriorly.
cluding the latissimus dorsi, teres major, cranial trapezius, caudal serratus anterior and
posterior deltoid, were always virtually silent
as the African apes quiescently stood quad-
rupedally. The two apes differed from one
another chiefly in the relatively greater incidences of low potentials in the gorilla’s
infraspinatus muscle and of moderate poten-
62
RUSSELL H. TUTTLE AND JOHN V. BASMAJIAN
Fig. 2 Orangutan female a, standing tripedally with the right hand fisted; b, standing quadrupedally
with both hands knuckled; c , fist-walking (note marked dorsiflexion of left wrist); and d, reaching overhead
from a quasi-bipedal posture with t h e right hand knuckled.
EMG OF PONGID SHOIJLDER MUSCLES AND QUADRUPEDALISM
63
a
Fig. 3 EMG recording of right a, sternocostal pectoralis major; b, teres major; and c , supraspinatus muscles in a n orangutan quasi-crouched alternately tripedally and quadrupedally on the floor while eating food
from t h e apex of a ramp. EMG activity increased from low to moderate levels in the supraspinatus (secs. 7121 as she eccentrically loaded t h e right forelimb while leaning forwards to lick t h e top of the ramp. t ; time in
seconds.
tials in t h e chimpanzee's supraspinatus
muscle.
In the quadrupedal orangutan, low potentials always occurred in the sternocostal pectoralis major muscle and they commonly also
appeared in the supraspinatus and subscapularis muscles (fig. 3). Unlike the African
apes, the orangutan's anterior deltoid muscle
remained silent during quadrupedal stance.
Many other muscles, including the latissimus
dorsi, teres major (fig. 3), cranial trapezius,
caudal serratus anterior, rhomboid, deltoid,
infraspinatus and teres minor, were silent in
the quadrupedal orangutan.
Tripedal stance
During tripedal stance, positions of the
forelimb were not noticeably different from
those employed in quadrupedal stance. Some
tripedal stances were only momentary, as
when grabbing or striking at objects and investigators, while those used during feeding
and reaching unimanually overhead might
last the better part of a minute before quadrupedal, bipedal or other postures were
adopted. Generally the level of EMG activity
did not change during long tripedal stances
unless there was bodily movement (fig. 3 ) .
Overall the EMG patterns observed during
tripedal stance in the three subjects are remarkablv similar to those exhibited during
"
quadrupedal stance. In addition, low potentials occurred in the gorilla's posterior deltoid,
in the chimpanzee's infraspinatus, and in the
orangutan's iliac latissimus dorsi muscles
and moderate potentials were sometimes
exhibited by the orangutan's supraspinatus
muscle during tripedal stance (fig. 3). These
are the major instances in which tripedal
stance appears to have induced higher levels
of EMG activity than quadrupedal stance did.
Descent onto the hand
Eccentric loadings of the forelimb during
descents from a ramp (fig. lb) and a level platform onto a knuckled (Pan) or fisted (Pongo)
hand commonly were accompanied by greater
EMG activity than was exhibited in tripedal
stance (table 1).This was particularly striking in t h e orangutan.
In all subjects, the three heads of the
deltoid, the supraspinatus, and, to a lesser extent, the infraspinatus muscles were quite
active during the supportive phase of descents
onto the hand. In the African apes there was
little difference in the EMG pattern of the
sternocostal pectoralis major muscle during
stance and the supportive phase of descents.
64
RUSSELL H. TUTTLE AND JOHN V. BASMAJIAN
facing anteriorly as i t did during the stance
phase. Position of the wrist generally changed
little between stance and swing phase. The
elbow was flexed slightly and the shoulder was
raised subtly so that the anteriorly swinging
hand cleared the substrate.
Like stance, locomotor positions of the hand
in the knuckle-walking, or more rarely, fistwalking chimpanzee varied more than in the
gorilla. For instance, the dorsum of his hand
sometimes faced laterad in stance phase, particularly during fist-walking steps.
The orangutan’s quadrupedal locomotion
Crutch-walking
was of shorter duration, more variable in
Crutch-walking was executed by swinging speed, and often appeared to be less well cooror sliding the flexed hindlimbs and torso be- dinated than that of the African apes. She
tween the abducted forelimbs. Knuckled (Pan usually walked with her hands tightly fisted
and with the dorsal aspects of proximal phagorilla, Pan troglodytes) or fisted fPongo pygmaeus) hands served as chief contacts with langes 11-V on the substrate (fig. 2c). She very
the substrate. Crutch-walking was infrequent rarely moved with a hand palmigrade. She
and consisted of only one or two steps per never knuckle-walked. The dorsum of the
locomotor bout on the floor or off the base of fisted hand faced anteriorly, laterad or interthe ramp. I t was accompanied by considerable mediately during stance phases. The extended
EMG activity while the forelimbs were sup- fingers were directed laterad during the
portive, expecially in the sternocostal pec- stance phase of palmigrade steps. The orangtoralis major, iliac latissimus dorsi, caudal utan often shuffled forward without fully
serratus anterior P a n gorilla only) and rhom- elevating her hand from the substrate during
boid (especially P. gorilla) muscles (table 1). “swing phase.” Unlike the African apes, in
We cannot attempt close comparisons among Pongo the shoulder did not pass over the supthe three subjects because our data is frag- portive hand during midstance phase.
During the stance phase of locomotor cycles,
mentary.
the sternocostal pectoralis major, intermediQuadrupedal locomotion
ate and posterior deltoid, and supraspinatus
For purposes of analysis and description we muscles were regularly active in all subjects.
arbitrarily divided each forelimb locomotor In the African apes, the pectoralis major gencycle into a stance phase, encompassing the erally acted a t low EMG levels throughout the
period between initial contact and release of stance phases of slow and moderately paced
the hand from the floor or ramp, and a swing locomotor cycles. Higher potentials sometimes
phase, embracing the period during which the accompanied rapid knuckle-walking though
hand was free of the substrate en route to lower potentials were still more common (fig.
final repositioning. Because release of the 4). Similarly, in Pongo both low and moderate
hand is initiated proximally by subtle eleva- potentials were exhibited by the sternocostal
tion of the shoulder and flexion of the elbow pectoralis major muscle at all locomotor paces
joint support does not occur throughout the and high potentials occurred rarely during
stance phase. Instead support is concentrated rapid fist-walking.
in t h e early and especially the middle segLow or moderate potentials characterisments of stance phase.
tically occurred in the intermediate and posteDuring the stance phase of locomotor cy- rior deltoid muscles of the three subjects durcles, the gorilla quite consistently placed her ing the stance phases of slow, moderate and
knuckled hand with the dorsum facing anteri- rapid locomotor cycles (fig. 4). In Pan and
orly (fig. lc). Concordantly, the ulnar olecra- Pongo the intermediate deltoid muscle gennon process was oriented laterad. During early erally commenced activity toward the end of
swing phase, the hand might be pronated so stance phase, before the elbow flexed and (in
t h a t the palm faced somewhat laterad (fig. Id) Pan only) before adduction of the wrist was
or it might be carried forward with t h e dorsum decreased. EMG activity continued as weight
Per contra, in the orangutan i t exhibited
potentials ranging from low to high. Similarly, the caudal serratus anterior muscle was
much more active in the orangutan than in
the African apes. High EMG potentials occurred more commonly in the anterior deltoid
and supraspinatus muscles of Pongo than in
those of Pan. The major notable difference between the shoulder muscles of the two African
apes during the supportive phase of descent is
the higher EMG activity of the subscapularis
muscle in the chimpanzee.
EMG OF PONGID SHOULDER M1JSCLES AND QUADRUPEDALISM
a
t
locomotor bouts, low potentials commonly occurred. In Pan troglodytes, t h e posterior
deltoid muscle generally was active during
pre-release and early swing phase of the hand,
especially during rapid knuckle-walking (fig.
4). Occasionally, it was silent throughout a
locomotor cycle or was only active during prerelease of the hand. In fist-walking Pongo
pygmaeus, the posterior deltoid muscle generally evinced either low or moderate and
rarely marked potentials during pre-release of
the hand and lower potentials during early
swing phase.
In Pun gorilla, the supraspinatus muscle
acted quite variably during quadrupedal locomotion. Some locomotor cycles were accompanied by virtually continuous low or widely
spaced single potentials while more commonly
consequential potentials were concentrated
during early swing phase. On a few occasions,
the supraspinatus muscle was silent during
swing phase, especially when knuckle-walking up and down the ramp. Hence it appears
that forward swing of the forelimb can occur
without action of the supraspinatus muscle in
the gorilla. EMG potentials, including some
high ones, often occurred when there was
noticeable lateral rotation of the humerus a t
the glenohumeral joint during initial and early swing phase, Sometimes the potentials
which occurred during stance phase were
highest a t pre-release of the hand, i.e., a t the
outset of repositioning the forelimb.
In Pan troglodytes, the supraspinatus muscle was virtually always active a t low or moderate levels during much of the locomotive cycle. Most commonly, it was active from the latter half of swing phase through the supportive
segments of stance phase. But on otter occasions, EMG activity occurred predominantly
during stance phase and only briefly or not at
all during swing phase. Characteristically, it
was silent a t pre-release of the hand.
In Pongo pygmaeus, the supraspinatus muscle was active a t various EMG levels ranging
from low to moderate during support phase,
especially from midstance through release of
the hand, and early swing phase. Sometimes it
was active only during pre-release and early
swing. I t was silent during some very slow
fist-walking bouts. Thus, in Pongo it seems to
he particularly related to the initiation of
manual repositioning during fist-walking a t
moderate and brisk paces.
In the African apes the infraspinatus mus-
*
1
2
3
4
5
6
sec.
Fig. 4 EMG recording of right a, sternocostal pectoralis major; and b, anterior; c, intermediate; and d, posterior deltoid muscles in a briskly knuckle-walking chimpanzee. a is active throught supportive aspects of stance
phase; b,c are chiefly active (low potentials) during mid
and late stance phase; d, acting to lift and perhaps also laterally rotate the arm, exhibits moderate potentials
during pre-release of the hand and swing phase. t, time is
seconds.
was removed from the hand. It ceased abruptly during the early segment of swing phase.
Like the pectoralis major muscle, the intermediate deltoid did not exhibit higher potentials during rapid locomotion unless the supportive forelimb was subjected to increased
loads. Indeed EMG activity was often quite
low during rapid locomotion on level surfaces unless quick turns were being executed
(fig. 4).
In Pan gorilla, the posterior deltoid muscle
exhibited EMG activity during pre-release of
the hand at the end of stance phase. During
rapid locomotion about the room with the
forelimb acting as a pivot for sudden turns,
the posterior deltoid probably contributed
notable propulsive force. But during other
65
66
RUSSELL 11 TUTTLE AND JOHN V BASMAJIAN
cle was commonly active briefly a t the outset
of manual repositioning, i,e., during pre-release and earliest swing phase. This is when
lateral rotation of the humerus at the glenohumeral joint. occurs. In the gorilla, moderate
potentials accompanied brisk knuckle-walking on the floor and ramp. EMG potentials
were generally low in the chimpanzee’s infraspinatus muscle even during brisk locomotion up and down the ramp.
In the chimpanzee and groggy gorilla, the
subscapularis muscle was sometimes active at
low levels during late swing and/or most of the
succeeding support phase. Thus it may be related to medial rotation of the humerus a t the
glenohumeral joint which occurs a t that point
in the locomotive cycle, In the fist-walking
orangutan, when low potentials occurred in
the subscapularis muscle they were confined
to the support phase as the humerus was
rotating medially a t the glenohumeral joint.
In the knuckle-walking apes, the cranial
trapezius muscle generally exhibited brief
bursts of quite low potentials at pre-release of
the hand. In the orangutan, very low potentials commonly accompanied pre-release of
the hand and continued well into swing phase.
However, in one locomotor bout, moderate
potentials occurred during the early swing
phases of several fist-walking steps.
In the gorilla, the caudal serratus anterior
muscle sometimes exhibited low potentials
during swing phases of moderately and briskly
paced knuckle-walking, On other occasions
only inconsequential single potentials or
silence accompanied knuckle-walking. In the
chimpanzee, knuckle-walking was usually accompanied by nil activity in the caudal serratus anterior muscle though occasionally
very low potentials appeared during the propulsive segment of stance phase. In Pongo
very low potentials occasionally accompanied
the early and midstance phase or pre-release
and early swing phase. But generally the caudal serratus anterior muscle was virtually
silent during fist-walking.
In the gorilla, the rhomboid muscle commonly exhibited low potentials during stance
phase, particularly when she used full versus
short forelimb strides and knuckle-walked
briskly on the floor and ramp. The chimpanzee’s rhomboid muscle acted at low levels
during release of the hand and early swing
phase of‘ brisk knuckle-walking and fist-walking on the ramp and floor. In Pongo, the rhom-
boid muscle exhibited low and moderate
potentials during late stance phases of fistwalking.
The anterior deltoid muscle of the gorilla
generally acted a t low and occasionally mode r a t e levels during t h e stance phase of
knuckle-walking. It was silent during swing
phase. In the knuckle-walking chimpanzee,
very low potentials characterized the anterior
deltoid muscle during stance phase (fig. 4)and
occasionally it was silent. In the fist-walking
orangutan’s anterior deltoid muscle only a
brief burst of very low potentials occurred at
the end of swing phase.
In summary, the following general features
emerge from this study re the role of shoulder
muscles during quadrupedal locomotion:
1. The sternocostal pectoralis major muscle
is a regular supporter of the upper body
weight and probably also a propulsive element during the stance phases of knucklewalking and fist-walking steps in all three
pongid apes.
2. The intermediate and posterior deltoid
muscles provide propulsive force during late
stance phase and concurrently they may
also augment st,ability in the shoulder complex.
3. The subscapularis muscle often contributes to support or propulsion or both
functions during stance phase. It probably
also contributes to stability of the glenohumeral joint by acting as a medial rotator
of the humerus.
4. Propulsion, support and shoulder stability may be augmented severally by the
rhomboid (P. gorilla, Pongo), supraspinatus
(P. troglodytes, Pongo), the anterior deltoid
(Pardt and the iliac segment of the latissimus dorsi (P. gorilla) muscles.
5. Release of the hand prior to repositioning
regularly involves the intermediate and
posterior deltoid and cranial trapezius muscles in all three great apes and the infraspinatus muscle (probably acting as a lateral rotator of the humerus) in the African
apes.
6. The supraspinatus was the only shoulder
muscle which was commonly active during
early swing in the three subjects. The
infraspinatus muscle also acted during early swing phase in the African apes.
7. During late swing phase, as the hand descended toward the substrate, the subscapularis muscle (probably acting as a medial
EMG OF PONGID SHOULDER MUSCIXS ANT) QUADRUPEDALISM
rotator of the humerus) was active in the
African apes whereas the anterior deltoid
muscle was active in the orangutan. Irregularly the iliac segment of the latissimus
dorsi muscle was active in the gorilla just
prior to hand contact.
DISCUSSION
Pongid versus other mammalian
quadrupedalism
Textbooks on mammalian functional morphology (e.g., Young, '57; p. 161; Leach, '61:
p. 159) commonly depict serratus anterior in
pronograde mammals as a postural muscle
which supports the upper body weight during
quadrupedal positional behavior. Our EMG
studies indicate that the thick caudal segments of pongid serratus anterior muscles do
not act consistently in accordance with this
model. In all subjects, the caudal serratus anterior muscles were silent during tripedal and
quadrupedal stances. And they were silent or
minimally active during the stance phases of
most locomotor cycles. It is possible that cranial digitations of pongid serratus anterior
muscles are more active during quadrupedalism.
As predicted by Young ('57: p. 161),the cranial trapezius did not serve as a postural muscle in our quadrupedal subjects. Unimpressive
EMG levels during the swing phases of
locomotor cycles highlight t h a t its principal
activity occurs during arm-raising in apes as
it does in orthograde man (Tuttle and Basmajian, '77).
Among the shoulder muscles which we
tested, only the pectoralis major and perhaps
the supraspinatus and subscapularis might be
singled out as postural muscles during static
terrestrial quadrupedalism in pongid apes.
This generalization might apply less to the
African apes than t o the orangutan, especially
when its forelimb is eccentrically loaded.
Stern et al. ('77) have published the only
EMG study on non-hominoid primate shoulder
muscles to which we can compare broadly our
results. They present highly condensed,
schematic renderings of EMG records from
the latissimus dorsi, caudal serratus magnus
(= anterior). middle ( = intermediate) deltoid, and pectoralis major muscles of two Ateles and one Lagothrix during pronograde
quadrupedalism along a horizontal branch.
In the ateline monkeys, the sternocostal ( =
caudal) pectoralis major muscle exhibited
67
uniphasic periods of EMG activity commencing a t mid (Lagothrix) or late (Ateles) swing
phase and ending during early (Lagothrix) or
mid fAteles) stance ( = support) phase of the
quadrupedal locomotor cycle (Stern et al., ' 7 7 ) .
This contrasts noticeably with the pongid apes
in which the sternocostal pectoralis major
muscle acted during most or all of the stance
phase and was silent during the swing phase
of quadrupedal locomotor cycles.
Like the pongid apes, the ateline monkeys
irregularly exhibited EMG activity in the
latissimus dorsi muscle during quadrupedal
locomotion. In Lagothrix, the low potentials
were confined to the late swing phase of the
locomotor cycle. In the fully alert chimpanzee
and orangutan, the latissimus dorsi muscle
was virtually silent during quadrupedal progression on the floor and ramp. The iliac segment of the latissimus dorsi muscle in the
gorilla sometimes exhibited low potentials
during late swing and most of the stance
phase as she progressed quadrupedally on the
floor. Once when she rapidly ascended the
ramp, moderate potentials occurred in the
iliac segment of the latissimus dorsi muscle as
she reached the apex (table 1).
The caudal serratus anterior muscle seems
to act quite variably in the ateline monkeys
and the pongid apes during quadrupedal
locomotion. Although the overall patterns of
activity in Ateles and Lagothrix are far from
identical (figs. 3, 5 in Stern et al., '771, both
species consistently evinced prominent EMG
activity during stance and swing phases of the
quadrupedal locomotor cycle. In the pongid
apes, the caudal serratus anterior muscle was
less consistently active than it was in the
ateline monkeys and i t exhibited only low
potentials. These were largely confined to the
swing phase in Pan gorilla; occurred only during the stance phase in Pan troglodytes; and
could occur during swing andlor stance phases
of moderately paced fist-walking in Pongo
pygmae us.
The intermediate deltoid muscle was consistently biphasically active during early and
mid stance phases and mid swing phases of
quadrupedal locomotor cycles in Ateles. This
pattern was only partly exhibited by Lagothrix during rapid progression. At slower
paces, Lagothrix evinced only a short period of
EMG activity toward the end of the stance
phase (Stern et al., ' 7 7 ) . Unlike Ateles, in the
pongid apes, the intermediate deltoid muscle
68
RUSSELL H. TUTTLE AND JOHN V. BASMAJIAN
acted chiefly during mid and especially late
stance phase and its activity generally continued into the beginning of swing phase.
We would need studies of branch-walking
pongid apes and ground-walking Ateles and
Lagothrix before we could attempt to attribute dissimilarities in EMG patterns of
their shoulders to differences between arboreal and terrestrial quadrupedalism versus
other factors.
Functional and evolutionary implications
The shoulder muscles of the three great
apes exhibited remarkably few major differences in overall activity pattern during
knuckling behavior - the entire spectrum of
static and locomotor hand postures in which
the dorsa of middle segments of digits 11-V are
the chief contacts with the substrate (Tuttle,
'75) - versus other modes of quadrupedalism
(except perhaps crutch-walking about which
we have limited data). This is strikingly
revealed during locomotor bouts wherein the
chimpanzee exhibited similar EMG patterns
during facultative fist-walking and knucklewalking steps, often interspersed with one
another.
Further, we found relatively few consistent
explainable differences between the muscle
activities of fist-walking Pongo and knucklewalking Pan gorilla and Pan troglodytes. Certain aspects of positional behavior, like the
supportive phases of descents onto the fist and
the stance phases of some bouts of fist-walking, seemed to elicit somewhat higher potentials in certain muscles of Pongo than their
counterparts in Pan. But the caveat r e too
fine-grained comparisons between EMG experiments must be recalled here. More controlled future studies, employing horizontal
and inclined treadmills, might reveal clearcut differences between the capacities of
orangutans and the African apes to sustain
terrestrial quadrupedal gaits.
That an orangutan can engage in a variety
of spontaneous short-term quadrupedal behaviors without continuous inordinately high
EMG potentials in its shoulder muscles is not
too surprising since orangutans are practiced
arboreal quadrupeds and adult males sometimes progress quadrupedally on the ground in
their natural habitats (see Tuttle, '77: pp.
284-287, for a review of current knowledge
about their naturalistic positional behavior).
Further, our experimental captive had had
ample opportunity to accommodate to terrestrial quadrupedalism. The eye-catching
structures of their shoulder girdles, which are
commonly linked to versatile arboreal climbing, suspensory behavior and overhead feeding, apparently are not extreme or uncompromising enough to require extraordinary
muscular effort during run-of-the-mill quadrupedal behavior. Ligaments and tendonized
components of muscles might be important
factors here. But whatever specific features
are operating, we may conclude that the
evolutionary transformation from a shoulder
complex similar to that of Pongo to ones like
Pan or vice versa probably would not be problematic vis-a-vis myological features. Such
transformations could probably occur rather
rapidly, especially in response to alterations
in the selective complex as would accompany
an increase in terrestrial or arboreal quadrupedalism.
ACKNOWLEDGMENTS
This study was supported mainly by NSF
grants GS-3209 and SOC75-02478 and by a
Public Health Service Research Career Development Award (1-K04-GM16347-01)from
the National Institutes of Health. Supplementary support was provided by NIH Grant RR00165 to the Yerkes Regional Primate Research Center and the Marian and Adolph
Lichtstern Fund of the University of Chicago.
We are especially thankful for the assistance
of Doctor G. H. Bourne, J. Malone, E. Regenos,
J. Perry, R. Pollard, S. Lee, R. Mathis, J.
Roberts, Doctor M. Keeling, Doctor M. Vitti, J.
Hudson, K. Barnes and C. Lin-Bodien.
LITERATURE CITED
Basmajian, J. V. 1974 Muscles Alive. Their Functions
Revealed by Electromyography. Third ed.The Williams &
Wilkins Co.. Baltimore.
Leach, W. J. 1961 Functional Anatomy, Mammalian and
Comparative. Third ed. McGraw-Hill Book Co., Inc., New
York.
Stern, J. T., J r . , J. P. Wells, A. K. Vangor and J . G. Fleagle
1977 Electromyography of some muscles of the upper
limb in Ateles and Lagot.hrix. Yearbook of Physical Anthropology - 1976. Vol. 20. pp. 498-507.
Tuttle, R. H. 1967 Knuckle-walking and the evolution of
hominoid hands. Am. J. Phys. Anthrop., 26: 171-206.
1975 Knuckle-walking and knuckle-walkers: a
commentary on some recent perspectives on hominoid
evolution. In: Primate Functional Morphology and Evolution. R. H. Tuttle, ed. Mouton, The Hague, pp. 203-212.
1977 Naturalistic positional behavior of apes
and models of hominid evolution, 1929-1976. In: Progress
in Ape Research. G. H. Bourne, ed. Academic Press, New
York, pp. 277-296.
EMG OF PONGID SHOULDER MUSCLES AND QUADRUPEDALISM
Tuttle, R. H., and J. V. Basmajian 1974a Electromyography of brachial muscles in Pun gorilla and hominoid
evolution. Am. J. Phys. Anthrop., 41: 71-90.
197413 Electromyography of forearm musculature in gorilla and problems related to knuckle-walking.
In: Primate Locomotion. F. A. Jenkins, Jr., ed. Academic
Press, New York, pp. 293-347.
1977 Electromyography of pongid shoulder rnus-
69
cles and hominoid evolution. I. Retractory of the humerus
and “rotators” of the scapula. Yearbook of Physical Anthropology . 1976. Vol. 20, pp. 491-497.
1978 Electromyography of pongid shoulder muscles. 11. Deltoid, rhomboid and “rotator cuff.” Am. J.
Phys. Anthrop., 49: 47-66.
Young, J. 2. 1957 The Life of Mammals. Oxford University Press, London.
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