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Angular displacement patterns of leading and trailing limb joints during galloping in monkeys.

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American Journal of Primatology 22:227-239 (1990)
RESEARCH ARTICLES
Angular Displacement Patterns of Leading and Trailing
Limb Joints During Galloping in Monkeys
JOEL A. VILENSKY, MARSHA MOORE-KUHNS, AND ANN M. MOORE
Department of Anatomy, Indiana University School of Medicine, Fort Wayne
The movement patterns of the joints of the right hind limbs and forelimbs
of four vervet and one squirrel monkey were compared during right- and
left-lead gallops. Although the overall displacement patterns were similar
under both conditions, comparisons of the inflection points in the curves
yielded consistent differences in the joints at various phases in the cycle.
Some of these differences appear to reflect differing mechanical conditions, whereas others seem to represent variation in muscle activation
patterns. Although some of the differences in the joints under the two
conditions were consistent with those reported previously for other quadrupeds, others were not. This may reflect that different quadrupeds use
slightly different biomechanical strategies during galloping.
Key words: primates, locomotion, gait, hind limb, forelimb
INTRODUCTION
Galloping is an asymmetrical gait in which each homologous pair of limbs
(fore- or hind) acts as a unit to propel the animal forward. When the forelimbs (or
hind limbs) strike the ground, one of the limbs typically makes contact shortly
before the other. The first limb to strike the ground is termed the trailing limb and
the second the leading limb [Hildebrand, 19771. Although this terminology appears to be inconsistent, it is based on spatial rather than temporal relationships.
That is, while both limbs are on the ground, the second to contact the ground is
positioned in front of (i.e., leading) the first to contact the ground. Because of this
apparent inconsistency, some prior reports on galloping have reversed the terms
[e.g. Miller & Van der Meche, 1975; Miller et al., 19751or have used different terms
such as first and second limbs [Cohen, 19791. For this report, we chose to retain the
classical terminology.
It is intuitively obvious that, because galloping is an asymmetrical gait and
because the homologous limbs do not strike the ground simultaneously, the conditions under which each limb contacts the surface differ. That is, the body and the
other limbs are in a somewhat different orientation when, for example, the right
forelimb contacts the ground compared with when the left does. For this reason as
well as because the nervous system may use the leading and trailing limbs slightly
Received for publication January 29, 1990; revision accepted J u n e 14, 1990.
Address reprint requests to Dr. Joel A. Vilensky, Fort Wayne Center for Medical Education, 2101
Coliseum Blvd., East, Fort Wayne, IN 46805.
0 1990 Wiley-Liss,Inc.
228 / Vilensky et al.
differently to achieve efficient propulsion, it is reasonable to expect variation in
the joint displacement patterns of leading and trailing limbs. The purpose of this
study was to determine if such variation exists in monkeys and, if so, to describe
it, analyze it functionally, and compare the results with the limited data available
for other mammalian taxa.
Regarding other taxa, for cats, Miller and Van der Meche [1975] presented
graphs of the angular displacement patterns of the forelimb joints of a single cat
when the limb was in trailing and leading positions, but the authors did not discuss
any differences in joint angular values apparent in the data. The actual graphs are
small and very difficult to use for comparative purposes because all the joints are
plotted on the same set of axes. In a second paper, Miller et al. [1975] presented
somewhat better graphs for the elbow and scapula joints as well as for the hip and
knee joints during trailing and leading conditions. The authors noted, based on
these graphs, again of a single cat, that the hind limb and forelimb of the leading
and trailing limbs have distinctive features. No quantitative analysis of angular
parameters was presented.
For dogs, Tokuriki [1974] stated that the joint displacement patterns are only
slightly different for the leading and trailing limbs. This evaluation was based on
a single animal.
The most comprehensive analysis available of differences in limb movement
patterns during galloping is for rats. Cohen [ 19791examined in detail the forelimb
joint displacement patterns of rats using X-ray cinematography of five animals
running on an exercise wheel. Unfortunately, although graphs are presented that
display notable differences in joint movement patterns, there is no tabular material detailing how consistent these differences were among the animals. In addition, the graphic comparison of right- and left-lead galloping use data from two
different animals, and there is no assurance that both animals were running at the
same speed. Thus, although Cohen’s [19791 study clearly indicates pronounced
differences in certain joint patterns, there is no indication of how consistently these
differences would appear in individual animals. Furthermore, no data are presented for hind limb joints.
For monkeys, the only available data regarding differences in trailing and
leading limb joint displacement patterns is an estimate by Larson and Stern [1989]
that, during swing, the trailing forelimb in vervet monkeys undergoes approximately half the excursion of the leading limb. To collect data for the present study,
we examined the lead author’s extensive collection of films of galloping vervet and
squirrel monkeys [see Vilensky & Patrick, 1985; Vilensky et al., 1988, 19903 to
determine if any of it was suitable for a highly controlled comparison of leading
and trailing limb joint displacement patterns. Specifically, we looked for animals
that switched leads during galloping at a set speed, i.e., within a filming trial. We
also required that each analyzed stride not be part of a transition. Although these
conditions were not met by many animals, we did find sufficient data to perform a
detailed study. It should be emphasized that, since we always filmed the animals’
right sides, all reported data are for right limbs. Thus this study controlled for any
potential asymmetry in limb movements of the two sides of the body as well as for
speed.
MATERIALS AND METHODS
All the film used for this study was taken under similar conditions with the
camera operating at a rate of 100 frameslsec except for one squirrel monkey trial,
in which the camera operated at 200 frameslsec. Prior to filming, the animals had
been trained to locomote at a variety of speeds on a treadmill that was enclosed
Galloping in Monkeys i 229
Fig. 1. Sketch of a vervet monkey illustrating the joint angles measured for this study. A, wrist joint; B, elbow
joint; C, shoulder joint; D, arm angle (anterior angle between arm and horizontal); E, hip joint; F, thigh angle
(anterior angle between thigh and horizontal); G, knee joint; H, ankle joint.
within a plexiglass cage. The lens of the camera was positioned 6 m from and
perpendicular to the long axis of the treadmill, and the animals ran so that their
right sides were closer to the camera.
As noted above, the films were examined to determine if any of the animals
changed either their forelimb or their hind limb leads for a single speed on the
same day (i.e., within a trial). For analysis, we required that there be a minimum
of two strides with the noted lead sequence within a trial, but the two strides did
not have to be consecutive. When possible, we used trials that had a t least three
strides with the desired lead sequences. It is also important to emphasize that,
when we chose strides that had forelimb lead changes, we did not control for hind
limb leads. We assumed that, within a gallop (when each homologous pair of limbs
acts as a unit), the displacement pattern of the forelimb joints (in the sagittal
plane) would not notably be affected by the lead pattern of the hind limbs. The
same applies when we chose strides that exhibited hind limb lead changes (i.e., for
those strides, we did not control for forelimb leads).
When more than three strides with a particular lead sequence were available
within a trial, we chose three to analyze based on the following two criteria: limbs
clearly visible and the monkey showing good posture on the treadmill (no crouching or other unusual behavior). For those strides we chose to analyze, an experienced technician used a cursor to input the estimated positions of the following
joint center locations into a computer: metatarsophalangeal, ankle, knee, hip,
shoulder, elbow, wrist, and metacarpophalangeal. From these x-y positions, the
computer determined the ankle, knee, hip, shoulder, elbow, and wrist angles as
shown in Figure 1. As indicated, the shoulder and hip angles were determined from
230 I Vilensky et al.
the joint center locations defining those angles (e.g., for the hip angle, the knee, hip
and shoulder joint centers; the shoulder angle was defined as the anterior angle so
that the same terminology could be applied t o movements at the hip and shoulder).
In addition, we also defined thigh and arm “angles” that were simply the relationship of that limb segment to the horizontal. It should be emphasized again that, in
all cases, only the movements of the right limb were analyzed. Thus this study
involved determining how this limb changed its movement pattern when it was
either trailing (i.e., left limb was leading) or leading. For the forelimb and hind
limb strides, a stride was considered to begin with right touchdown and end at the
frame preceding the next right touchdown.
For the forelimb lead changes, data from four animals were available. Data for
animal 1 (Al), a 2.3-year-old female vervet monkey, were available for two speeds,
2.58 and 2.81 m/sec. A2, an adult male vervet, exhibited forelimb lead changes at
2.58 m/sec. A3, a 2- year-old female vervet, showed a forelimb lead switch a t 2.81
mlsec. A4, an adult female squirrel monkey, showed forelimb lead changes at 2.28
m/sec. In addition, we used data for this animal for which there was about an 8%
variation in speed for the forelimb lead changes, specifically, 1.8 and 1.95 misec.
This occurred because the treadmill was still accelerating when one of the lead
changes occurred. We used these data despite the variation in speed so that we
would have a second set of data points for this animal, our only representative of
this species. For the hind limb, data were available for A2 at 2.58 misec and for A4
at 2.28 and 2.58 m/sec. In addition, data were available for one other vervet monkey (A5), an adolescent female (exact age unknown), for 2.28 and 2.81 m/sec.
The following number of strides were available for each animal: A l , three
strides for both types of forelimb leads at both speeds; A2, three strides for both
types of forelimb leads, three strides for left hind limb lead (LHL), and two strides
for right hind limb lead (RHL); A3, three strides for left forelimb lead (LFL) and
two for right forelimb lead (RFL);A4, three LFL strides at 1.95 d s e c and two RFL
strides at 1.8m/sec, at 2.28 m/sec three of both types of forelimb and hind limb lead
strides, and at 2.58 m/sec three LHL strides and two RHL strides; and A5, three of
both type of hind lead strides a t both speeds.
Once each stride was digitized and the angles computed, plots of the angles
were printed. From these plots, the values of the joints at the major flexionextension (or extension-flexion) turning (inflection) points were determined. Usually, these points were the highest or lowest before a definitive trend in the reverse
direction was apparent (see Fig. 2). We applied the traditional Phillipson nomenclature [see Wetzel and Stuart, 19761 to these inflection points. Briefly, in this
system, for a typical joint (e.g., ankle in Fig. 2), an epoch of flexion (yield) that is
designated the E2 phase begins at touchdown. Sometime later during stance, the
joint begins to extend, beginning the E 3 phase. Thus we called the inflection point
between the two, the E2-E3 transition. During late stance, a typical joint then
begins to flex again, beginning the F phase, with an E3-F transition between the
two. During the F phase, the foot loses contact with the ground and the swing
period begins. Finally, later during swing, the joint begins to extend again, beginning the E l phase. The El-E2 transition then occurs a t touchdown of the foot. It
is noteworthy that not all the joints analyzed followed the Phillipson pattern.
Specifically, the arm, shoulder, thigh, and hip joints did not show an El-E2 or an
E2-E3 transition because they did not yield (flex) a t touchdown (no E2 phase). For
these joints, we defined an E2-E3 transition as occurring at touchdown even
though no actual inflection point occurred at this time (see hip in Fig. 2). This was
done so that the touchdown angles could be compared across the animals. The wrist
did not show an E l phase and therefore did not exhibit F-El or El-E2
P
2c
80
120
0
195
50
50
PERiEh7 OF CYCLE
E2-E3
75
75
103
103
BO
00
25
50
75
103
25
50
PERCENT OF C Y C S
75
100
30
25
50
75
P i a t f L n OF ~ C L E
HI?
Fig. 2. Displacement patterns for the noted joints of the right limbs of A2 for locomotor cycles (beginning with touchdown) during which the right limb was
leading (solid lines) and the left limb was leading (right limb trailing; dotted lines). In addition, the inflection points on the curves are labeled according to
the nomenclature describled in the text. For the forelimb graphs, lift-off occurred a t 47% of the cycle, whereas, for the hind limb graphs, it occurred a t 44%
of the cycle. RFL = right front lead; LFL = left front lead; RHL = right hind lead; LHL = left hind lead.
25
25
W?’S
100
232 I Vilensky et al.
transitions. However, we did define the wrist touchdown angle to be equivalent to
the El-E2 transition.
For all digitized strides, we determined the values of the joints a t the described
inflection points. We then computed mean values and standard deviations for each
animal for each set of strides associated with a particular lead sequence. Finally,
because this study was based on a small number of animals, presentation of the
data is confined to descriptive comparisons using means rather than conclusions
based on inferential statistical procedures.
RESULTS
Forelimb Joints
Figure 2 depicts the joint displacement patterns for A2’s right hind limbs and
forelimbs, during both right and left lead conditions, beginning at limb touchdown.
For the forelimb graphs, lift-off of the limb occurred at approximately 47% of the
cycle, whereas, for the hind limb graphs, lift-off occurred at about 44% of the cycle.
Clearly, there were no gross differences in displacement patterns for the right limb
(fore- and hind) whether it was leading or trailing. There were, however, notable
differences in some of the inflection point values for some of the joints. These
differences, as well as those for the other animals, are graphically depicted in
Figures 3 and 4.
Figure 3 depicts the mean forelimb joint values at the noted inflection points
for all the angles for all the animals. Each type of symbol in the graph corresponds
to a different animal, with the filled symbols being associated with the LFL condition (i.e., right limb trailing) and the open symbols with the RFL condition.
Standard deviations are also indicated (upward bars for the LFL condition and
downward bars for the RFL condition). Two sets of similar symbols refer to the two
speeds used for that animal, with the slower speed to the left. For the El-E2
transition (Fig. 3A), neither the wrist nor the elbow exhibited any consistent
changes across the animals. At the E 2 4 3 transition (Fig. 3B), the wrist was
generally more flexed in the LFL condition, whereas the elbow joint did not exhibit
any consistent changes across the animals. For the arm, across the three vervet
monkeys (Al-A3; circles, triangle, and square), when the limb was trailing, it
tended to be less protracted a t E2-E3 (touchdown) than when it was leading. The
reverse, however, tended to be true for the squirrel monkey (A4; diamonds). Differences in angles were also clearly apparent for the vervet monkey shoulder
angles, whereas the squirrel monkey had similar shoulder angle values across both
conditions.
For the elbow at E3-F (Fig. 3C), all the vervets showed slightly higher values
(greater extension) during right leads, but this was not true for the squirrel monkey. The arm angle at E3-F showed a marked consistent difference across all the
animals. The arm was always more retracted (extended) at E3-F when the left
limb was leading. For the shoulder, the reverse was true, with the angle being
consistently greater (more retraction) when the right limb was leading. Only the
shoulder showed a consistent difference at the F-El transition (Fig. 3D). The angle
was always less (more protraction) when the right limb was leading.
Hind Limb Joints
For the hind limb joints, there were no consistent differences at the El-E2
transition (Fig. 4A). At the E2-E3 transition point (Fig. 4B) the thigh showed
consistent differences, being notably more protracted when the right hind limb was
leading. A similar but less marked trend was evident for the vervet monkey hip
angles, but this was not true for the squirrel monkey.
Galloping in Monkeys / 233
A EI-EZ
WRIST
FCBOW
220
r
170
120
L
120
T
L
ARM
B. E2-E3
SHOULDER
100 r
v?
I
Y
g
n
130
120
110
100
90
80
70
-
-
6 @2 "
8 0- - Q 8 a i
70
-
-
9 0 - T
130
4
90 -
50 40 30 -
30 1
170,
110
I
Fig. 3. Mean angular values for each of the noted forelimb joints at the El-E2 (A), E2-E3 (B), E3-F (C), and
F-El (D) inflection points. The circles correspond to Al, the triangles to A2, the squares to A3, and the diamonds
to A4 (squirrel monkey). Filled symbols correspond to the LFL condition and open symbols to the RFL condition.
Where two pairs of similar symbols are presented, each pair corresponds to a specific speed for that animal, with
the slower speed on the left (see text). The bars indicate one standard deviation (directed upward for the LFL
condition and downward for the RFL condition).
For the E3-F transition (Fig. 4C), there were consistent differences for all the
joints. For the ankle, the value was always higher (greater plantarflexion) when
the right limb was leading. The knee was also always more extended when the
right limb was leading. The thigh and hip were both notably more extended (retracted) when the left limb was leading.
At the F-El transition (Fig. 4D), the ankle showed no consistent differences
among the monkeys. For the vervets, the knee was more flexed when the right
limb was leading. For the thigh, the segment was always less protracted when the
limb was trailing. This was also true for the vervet monkey hip joint but not for the
squirrel monkey.
Effects of Speed
Speed did not consistently affect the relationships between the joints when the
limb was in a leading or trailing position. In general, similar differences were
apparent at both speeds for the animals for which data were available for more
than one speed.
234 I Vilensky et al.
A El-EZ
150
KNEE
ANKLE
r
HIP
THIGH
50
100
* i
0 0
“
70
A
60
180
10
w
W
CT
150
160
V
- v
140 -
V
*
*
A
A
130 120 -
Fig. 4.
50
-
i70 160 -
y
90
I
*
0
’
~
140 I30
1
20 1
160 -
140 -
140 -
120
20
120 110
100 -
- v v
100 -
~
100
~
A
~
80
~
Q
8060 -
v v
i s +
a q o
Mean angular values for each of the noted hind limb joints at the El-E2 (A), E2-E3 (B),E3-F (C), and
F-El (D) inflection points. The downward-pointing triangles correspond to A5, the upward-pointing triangles
to A2, and the diamonds to A4. Filled symbols correspond to the LHL condition and open symbols to the RHL
condition. Where two pairs of similar symbols a r e presented, each pair corresponds to a specific speed for that
animal, with the slower speed on the left (see text). The bars indicate one standard deviation (directed upward
for the LHL conditon and downward for the RHL condition).
DISCUSSION
To facilitate the discussion of the data presented in the previous section, Figure 5 depicts tracings of A2 during all four conditions. These tracings were taken
from alternate frames of the original films (thus each tracing is separated from the
next by .02 sec). Each tracing is numbered consecutively and the tracing that is
associated with each of the transition points is noted for each joint.
Forelimb Joints
For the vervet monkeys, the greater arm and shoulder protraction with a right
lead a t E2-E3 is associated with the fact that, under this condition, the fore part
of the body is already supported by the trailing limb, so the leading limb can
outstretch further to increase stride length. This is clearly seen in tracings No. 1
in Figure 5A. The slightly greater wrist dorsiflexion with a left lead a t the E2-E3
transition point may be associated with the fact that, because the right was the
first limb t o strike the ground, it showed an increased “yielding” or shock-absorbing (E2) phase. The tendency toward greater elbow extension at E3-F with a
right lead may be associated with the limb (being the last to leave the ground)
exerting more of a thrust as it does so. The greater retraction of the arm a t E3-F
Galloping in Monkeys I 235
when it is trailing probably relates t o the other limb still supporting body weight
and thus allowing a greater degree of excursion. The difference in shoulder angles
at E3-F, as is apparent from the tracings, relates to differences in the elevation of
the hind part of the body as well as to differences in arm protraction (see above).
The differences in the shoulder values a t the F-El transition occur for the same
reason as described above for the E2-E3 transition (see Fig. 2).
Hind Limb Joints
The thigh at touchdown (E2-E3) is more outstretched (more protracted) when
the limb is leading. This is obvious in comparing tracings No. 1 in Figure 5B.
Apparently, the increased protraction of the leading limb is permitted because the
limb is striking the ground while the contralateral limb is supporting much of body
weight. This explanation also applies to the vervet hip at E2-E3.
The difference in ankle plantarflexion a t the E3-F transition seems clearly to
be related to the fact that, when the right limb is leading, it is the last to leave the
surface and therefore, at lift-off, it imparts a final substantial thrust (compare
tracings No. 9). The increased extension for the knee when the right limb is leading would similarly be associated with this final thrusting action. It is clear from
the tracings that this thrusting raises the hind section of the body as well as
propels the animal forward. The increased thigh and hip extension at E3-F when
the limb is trailing is probably associated with increasing stride length (see above).
The increased flexion of the leading knee at the F-El transition appears to be
associated with the increased elevation of the hind portion of the body. This probably slightly increases the swing duration of that limb. The difference in protraction of the thigh (hip) a t the F-El transition occurs for the same reason as at the
E2-E3 transition (touchdown); the leading limb can reach farther forward to increase the stride.
Comparisons Between the Hind Limbs and Forelimbs
At touchdown, the leading limb (fore- or hind) is more protracted, which, as
noted above, is probably related t o increasing stride length. At E3-F, the ankle
was more extended (plantarflexed) when the limb was leading. We suggested that
this increased plantarflexion was related to a final push-off by the leading hind
limb. In contrast, the wrist did not show consistent E3-F differences. This finding
suggests that the wrist does not provide much propulsive force. The elbow and knee
both tended t o be more extended at E3-F when the limb was leading, which
presumably is associated with more power at lift-off. On the contrary, the arm and
thigh were both more extended (retracted) at E3-F when the limb was trailing.
This probably acts to increase stride length (see above). At F-El, the knee showed
a prominent difference, whereas the elbow did not. We suggest that this relates t o
the elevated position of the hind portion of the body at this stage (see above). The
fact that the arm did not show a notable difference at F-El, whereas the thigh did
probably reflects that this turning point was often ill-defined for the proximal
joints (see Fig. 2). However, the hip and shoulder tended to be in accord for the
F-El point, with the limb being more protracted when it was leading.
ComparisonsWith Prior Reports
As noted previously, for vervets, Larson and Stern [1989] estimated that during swing the trailing forelimb undergoes approximately half the excursion of the
leading forelimb because the trailing limb ends swing phase in a less protracted
state than the leading limb. We did not measure “limb excursion” during swing,
but our data do indicate that the trailing arm a t touchdown is less protracted than
Ankle
-
El E2 (1)
E2 - E3 (5)
€ 3 - F (9)
F - E l (15)
Arm
Thigh
E2 - E 3 (1)
E 3 - F (10)
F - E l (21)
Arm
E2 - E 3 (1)
E 3 - F (11)
F - E l (20)
E2 - E3 (1)
E 3 - F (13)
F - E l (21)
Hip
E2 - €3 (1)
E 3 - F (9)
F - E l (19)
-
Shoulder
E2 E3 (1)
E 3 - F (11)
F - E l (20)
-
Shoulder
E2 € 3 (1)
E 3 - F (12)
F - E l (21)
Ankle
El - E2 (1)
E2 - €3 (5)
€ 3 - F (gj
F - El(15)
E2 E3 (5)
€ 3 - F (10)
F - E l (14)
-
Knee
E l - €2 ( 1 )
Fig. 5
E 3 - F (10)
F - €1 (21)
Thiah
E2 - €3 (1)
E2 - E 3 (1)
E 3 - F (8)
F - E l (18)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - - - - - - - -
El - E2 (1)
E2 - E 3 (5)
E 3 - F (9)
F - E l (18)
El - E2 (1)
E2 - E 3 (4)
€ 3 - F (8)
F - El (14)
Elbow
Wrist
El - € 2 (1)
E2 - E3 (6)
E 3 - F (12)
- E2 (1)
- E 3 (4)
F (10)
- El (16)
El
E2
E3F
Wrist
El - E Z ( 1 )
E2 - E3(6)
E 3 - F (11)
Galloping in Monkeys I 237
the leading limb (Figs. 3B, 5A). This is at least in accord with Larson's and Stern's
observation.
Data from Miller et al. [19751 for the cat elbow indicate major differences for
the E2-E3 and F-El transitions. In both cases, there was more flexion in the
trailing limb (it is important to note that we have reversed the terminology Miller
et al. present in their Fig. 4 because they used leading and trailing in a temporal
rather than spatial sense). Our results do not indicate any consistently greater
flexion for the elbow at the E2-E3 or F-El transitions for the trailing limb.
Regarding the hind limb, the hip joint of the cat showed no notable differences
when the limb was in the trailing or leading position [Miller et al., 19751. For the
knee, there was markedly greater flexion at E2-E3 and more extension a t E3-F
in the trailing limb. The lack of differences for the cat hip joint is surprising
compared to the monkey data, although it is possible that variation in measurement techniques accounts for the differing results. For the knee at E2-E3, the
monkeys did not show consistent differences, but at E3-F, when the limb was
trailing, contrary to the case in the cat, the knee showed less extension than when
it was leading.
For rats, Cohen [19791 found that the elbow joint differed in trailing and
leading limbs at E3-F, F-El, and particularly El-E2, whereas, at E2-E3, the
elbow had similar values. At E3-F, the rat elbow was more extended in the leading
limb; at F-El, the elbow was more flexed in the trailing limb; and, at El-E2, the
trailing elbow was much more extended. The similarity at E2-E3 and the differences at El-E2 resulted in the range of yield (E2 phase) being much greater in the
trailing elbow. In comparison, for the monkeys, we also found greater extension in
the leading limb a t E3-F but no consistent differences at F-El or El-E2. Interestingly, although the vervets did not show greater yield range (E2) at the elbow
when the limb was trailing, the squirrel monkey did (about 12" greater).
Cohen El9791 also measured the humerus angle of the rats, which is the same
as our arm angle. For this angle a t the E3-F transition point, the trailing limb had
notably more retraction than the leading limb. In the monkey, the trailing limb
also showed more retraction.
Neural Control and Functional Anatomy
The data presented here demonstrate conclusively that leading and trailing
limbs in monkeys do not undergo identical movement patterns. Although the
differences may reflect primarily the differing mechanical conditions associated
with the overall positioning of the body, in some cases, e.g., increased ankle plantarflexion in the leading limb a t E3-F, there may be controlled changes in muscle
activation patterns in order to maximize efficiency of force production. Accordingly, Cohen and Gans [19751 showed differences in rat triceps muscle activation
sequences for leading and trailing limbs. More directly related to the present
study, Larson and Stern El9891 found differences in the pectoralis major and latissimus dorsi muscles for the leading and trailing forelimbs of vervet muscles.
Specifically, they reported an increase in the activation of the caudal part of the
pectoralis major and latissimus dorsi during late swing phase in the trailing limb.
The authors associated this increase with the reduced protraction of the trailing
Fig. 5. Tracings of A2 taken from alternate film frames (.02 sec apart) during RFL and LFL strides (A) and
during RHL and LHL strides (B). Each set of tracings represents a complete locomotor cycle. For each set, the
location of the various inflection points for each joint are indicated by referring to the numbers located beneath
each of the tracings.
238 I Vilensky et al.
limb a t touchdown (see above). Thus these muscles are described as “slowing down
the swinging limb.”
The EMG data and our data indicate that there is consistent asymmetry in the
neural control systems of the two sides during galloping. Perhaps it is sensitivity
to the amount of asymmetry in the system that is one cause of frequent lead
changes in quadrupeds. Other suggested causes are “whim” [Howell, 19441, fatigue
[Dagg, 19771,and prevention of excessive lateral excursions of the center of gravity
[Wetzel et al., 19771.
The facts that the vervets and the squirrel monkey were sometimes not consistent in the differences found for the leading and trailing limb joints and that
there were differences among the monkeys, cats, and rats suggest that variation in
body design may result in slightly different galloping strategies. Accordingly, Jenkins [1971] stated that there is not a single mode of posture and locomotion among
terrestrial mammals. In addition, the fact that primates may be more dependent
than typical quadrupeds on their hind limbs for propulsion may also account for
some of the differences [see Kimura et al., 1979; Kimura, 19851. (However, i t is
noteworthy that there is some question of the applicability of the findings of
Kimura and colleagues to high speed gaits [see Vilensky, 19891.)
CONCLUSIONS
1. The overall displacement patterns of the limb joints are similar during
leading and trailing conditions.
2. Despite the similarity, there are notable differences in the values of some of
the inflection points for the joints when the associated limb is leading or trailing.
3. In some cases the differences in joint values probably reflect only differing
mechanical conditions, whereas in others, differences in muscle activation patterns
are likely.
4. The facts that the monkeys were not always similar among themselves
(especially the vervets compared to the squirrel monkey) and that a s a group they
deviated from other species indicate that different animals may use slightly different biomechanical strategies during galloping.
5. It is possible that the asymmetry in the neural control programs associated
with the leading and trailing limbs is a causal factor in the frequent lead changes
commonly seen in animals.
ACKNOWLEDGMENTS
We are grateful to Mr. Gregory Duncan for assistance during filming, Ms.
Diana Jackson for typing the manuscript, and Ms. Roberta Shadle for drawing
some of the illustrations. Support for this study was provided by the Indiana
University School of Medicine.
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