ArticlePDF Available

Kinematic Analysis of the Locomotion of the Polar Bear (Ursus Maritimus, Phipps, 1774) in Natural and Experimental Conditions

Authors:

Abstract and Figures

The striking ability of the polar bear to travel on ice or frozen snow is tentatively related to different structural features involved in the locomotor behaviour of the animal. A comparison with the brown bear shows the specific features, in gaits, leg movement and in ground contact structures. It is suggested that these specific features constitute a functional complex adapted to locomotion in polar environment. During slow gaits, polar bear hind limbs are maximally extended. The legs are able to resist the transfer of mass during the contralateral limb swing phase. This results in a walk with swaying hips. The polar bear uses transverse gallop to improve stability, whereas the brown bear uses rotary gallop. The polar bear is comfortable on slippery wet substrate, while the brown bear is reluctant to move on it. Proximodistal alternation of pads and large zones with hair constitute the main characteristics of the plantar and palmar soles of the polar bear. These features may constitute a functional specialization for the drainage of water from the feet, the reinforcing of adhesion and an increase in the area of contact (snowshoe). The drainage is produced by two kinds of structures: the superficial network of the epidermis of the pads and the hair between the pads. These hirsute zones absorb the liquid which is drained off the pads by the animal's weight during the stance phase. The hairs are also present in the regions of the soles where thrusts are transmitted to the ground.
Content may be subject to copyright.
KINEMATIC ANALYSIS OF THE LOCOMOTION OF THE
POLAR BEAR (URSUS MARITIMUS, PHIPPS, 1774) IN
NATURAL AND EXPERIMENTAL CONDITIONS
by
S. RENOUS, J.-P. GASC and A. ABOURACHID
(URA
1137 CNRS/MNHN,
Laboratoire d'Anatomie Comparée,
Muséum National
d'Histoire Naturelle, 55 rue Buffon,
75005 Paris, France)
ABSTRACT
The striking ability of the polar bear to travel on ice or frozen snow is tentatively
related to
different structural
features involved in the locomotor behaviour of the animal. A comparison
with the brown bear shows the specific
features,
in gaits, leg movement and in ground contact
structures. It is suggested
that these specific
features constitute
a functional
complex adapted
to locomotion
in polar environment.
During slow gaits, polar bear hind limbs are maximally extended. The legs are able to
resist the transfer of mass during the contralateral limb swing phase. This results in a walk
with swaying hips. The polar bear uses transverse gallop to improve stability, whereas the
brown bear uses rotary gallop. The polar bear is comfortable on slippery
wet substrate,
while
the brown bear is reluctant to move on it.
Proximodistal alternation of pads and large zones with hair constitute the main charac-
teristics of the plantar and palmar soles of the polar bear. These features may constitute a
functional specialization
for the drainage of water from the feet, the reinforcing
of adhesion
and an increase in the area of contact (snowshoe). The drainage is produced by two kinds
of structures: the superficial
network of the epidermis
of the pads and the hair between the
pads. These hirsute zones absorb the liquid which is drained off the pads by the animal's
weight during the stance phase. The hairs are also present in the regions of the soles where
thrusts are transmitted to the ground.
KEY WORDS:
locomotion, kinematic,
polar bear, Ursus maritimus,
brown bear, Ursus arctos.
. INTRODUCTION
The polar bear shows a spectacular ability to move with different gaits on
snow, a substrate with weak cohesiveness, and ice, a substrate with a low
friction coefficient. The ability to run on ice suggests a control of dynamic
balance due to limb coordination and efficient morphofunctional systems
to match the specific characteristics of the substrate. Few papers deal with
polar bear locomotion. According to HARINGTON
(1970), and VAN WORMER
(1966), Ursus maritimus is able to walk, gallop and perhaps pace, but it
146
never trots. DAGG (1973), in her review of mammalian gaits, emphasizes
the confusing data concerning bears. In the polar bear, a good grip on the
ice may be explained by the organisation of locomotor cycle of fore and
hind limbs in slow and fast gaits. The structure of the palmar and plantar
surfaces may also contribute to the ability to move on snow and ice.
For this reason, the present paper analyzes the action of the locomotor
system of the polar bear on several substrates. The analysis is based upon
films taken in natural conditions and a set of experiments performed on
zoo animals. A comparison with the brown bear, Ursus arctos, allows the
interpretation of the specific locomotor characteristics of the polar bear.
MATERIALS AND METHODS
Materials
Two polar bears (Ursus maritimus), a male of 900 kg and a female of
approximately 500 kg, were filmed at the zoo of Vincennes (National Mu-
seum of Natural History) using a Sony HI8 video camera (25 frames/sec).
These kinematic data were complemented by other films of Ursus mar-
itimus (producer: Rémi Marion) showing locomotion under natural condi-
tions at Churchill (Manitoba, Canada) and various parts of the polar region
(Canal + Video: l'ours blanc). In order to visualize movements of the
different skeletal elements of the limbs during locomotion, we used artic-
ulated skeletons and single bones (Museum national d'Histoire naturelle
(M.N.H.N.), Comparative Anatomy collections). Plaster casts of the palmar
and plantar surfaces of a polar bear were obtained from the Laboratory of
Zoology (Mammals and Birds) of M.N.H.N. The footprints of two brown
bears (Ursus arctos; 700 kg) were taken in Vincennes Zoo for comparison.
Methods
The analysis of the gaits is based upon the record of periodic events: the
duration of one complete motion cycle (i.e., stride) starting with the place-
ment of a reference limb (often a hind limb) on the ground, the duty factor,
time lags between diagonal or homolateral limbs, fore and hind leads, the
leading foot being the second of a pair touching down in each couplet
(HILDEBRAND, 1962).
Film sequences of locomotion on soft or frozen snow, ice (in the field) or
concrete surfaces at the zoo were selected to analyze the gaits. In the se-
quences selected, the bears moved at steady speed (measured by the regular
displacement of the hip during approximately ten cycles) and perpendicular
to the direction of the camera to ensure a lateral view. The duration of
147
the total limb cycle, the stance phase, and the time lag between footfalls
of diagonal limbs (for example: right fore limb and left hind limbs RF-LH
and left front and right hind limb LF-RH) and between homolateral limbs
(for example: RF-RH and LF-LH) were measured to specify the type of co-
ordination. Each contact lasts the same fraction of the cycle and the cycles
showing large differences in limb contact duration were eliminated. The
characteristics of the gaits were finally identified according to HILDEBRAND
(1966, 1976, 1977).
As most of the proximal parts of the limbs are covered by the fur, the
estimation of the anatomical position of the joints was based upon the
observation of the bulbing of the large muscles in moving animals. The
successive articular joints of the fore and hind limbs were identified in
sequences showing lateral, front or back views of the polar bears. The
coordinates of the joints and the angular variations were analyzed with a
digitizing video system (Optimas software).
Footprints of the polar and brown bears were obtained at the zoo on
various substrates. To reach the outside area from their cage, the animals
had to pass through two rooms separated by narrow doors. The floor of the
first room was covered by a mat that was impregnated with paint. Footprints
were recorded on various substrates (sheets of smooth and very strong paper,
sheets of absorbent and thick paper, perspex) that were firmly attached to the
floor of the second room. Sony HI8 video cameras using 25 frames/sec were
fixed into the rooms outside of the reach of the animals. The experiments
were repeated at regular intervals to accustom the bears to the experimental
set up and to obtain a continuous gait without trampling on the substrate.
RESULTS
In all mammals (JENKINS, 1971; FISCHER, 1992; ROCHA-BARBOSA et al.,
1996a, 1996b), each limb has a periodic motion. Cineradiographical analy-
sis of the locomotion of the guinea pig clearly shows the basic component
of the mammalian locomotor cycle (ROCHA-BARBOSA et al., 1996; fig. 1).
Each cycle consists of a stance and a swing phase (GOSLOW et al., 1981).
The touchdown is followed by a yield subphase of the stance (E2) charac-
terized by the activity of extensor muscles (ORSAL, 1987), which act against
gravity and inertial effects. An elastic storage of energy may occur at this
moment in muscular and tendinous elements. The propulsive subphase (E3)
starts when the proximal element of the articular chain, transmitting part
of the body mass, passes over the point of support. An extension of the
limb, resulting from the action of the extensor muscles, causes the thrust
against the ground to create the propulsive force. When the limb takes off
148
149
the ground (F) at the beginning of the swing, it is accelerated forward and
flexed by the action of the flexor muscles. It is extended and decelerated
(El) by the action of the extensor muscles to contact the ground again for
a new cycle.
Asymmetrical gaits
Polar bears observed at the zoo or in the wild used slow, moderate or fast
walks and slow run and pace (fig. 2) as defined by HILDEBRAND
(1966). The
leg sequence was always lateral, the fore footfall following the ipsilateral
hind footfall (fig. 3). The gait used in the zoo was always moderate pacing
walk. In the films analysed, polar bears moved on hard snow or on fine
snow using all the gaits, from slow walk to running pace. On ice, they
used moderate walk, which was also observed on soft snow when the snow
sank beneath their feet. An unusual locomotor behaviour was observed on
ice: the hindfeet were used as in bipedal locomotion propeling the body
forward, while the forefeet slided on the ice. A very long sequence of a
young, showed a cub playing with an ice ball with the forefeet, using only
the hindfeet for locomotion.
To analyse the movement of the fore and hind limbs, we chose a cycle of
fast walk in lateral view (fig. 4A and B; duty factor: 0.63; interval between
the fore footfall and thc ipsilateral hind footfall in percent of the cycle:
13%) lasting approximatively 1.48 second and beginning with the step of
the left forelimb. The skeleton segments were superimposed on the outlines
of the limbs.
The stance began with a special subphase (FE) lasting 20% of the support
phase, which was characterized by a gradual extension of the limb. This
was followed by a short yield subphase (E2) 0.24 s, 25% of the stance)
occuring after the shoulder or the hip passed vertically over the hand or foot
contacts. The yield subphase was marked by little flexion of the shoulder,
the elbow and the wrist joints in the fore limb and by a larger flexion of
the knee and the ankle joints in the hind limb. The hip was more or less
stable. The beginning of the yield of a limb corresponded to the moment of
the take-off of the contralateral limb. Consequently, at the beginning of the
swing phase of one limb a part of the body mass was transferred to the other
limb, which was in extended position, its skeletal elements constituting a
Fig. 1. Locomotor
cycle. A: typical phases of the hind limb locomotor
cycle of a guinea pig.
E2 and E3 (stance), F and El (swing) during a trot, with corresponding general movement
of the leg (1, 2, 3 and 4). The minimal value of the sum (in rad) of the main angles of
the chain, ilio femoral (a), femoro tibial (b) and tibio tarsal (c), define the limits of both
phases of stance and of swing. B: a comparison
with the same cycle of a walking polar bear.
FE, subphase
of full extension.
150
Fig. 2. Gait diagrams of the polar bear. A: slow walk, B: medium slow walk, C: fast walk.
Stance phase is indicated by a thick line and swing phase by the absence of a line. Time is
given in percent of the reference cycle (LH). LF, left fore limb; LH, left hind limb; RF, right
fore limb; RH, right hind limb. -
151
Fig. 3. Graph of distribution
of symmetrical gaits of polar bears on different substrates sho-
wing the use of a lateral sequence (from HILDEBRAND,
1966).
vertical column. The propulsion subphase (E3) lasted approximately 55% of
the stance and was characterized by an extension of the wrist joint, whereas
the shoulder joint was flexed. The elbow was locked at maximal extension.
The hind limb showed an extension of the hip and ankle joints whereas the
knee was flexed (fig. 4).
The swing of the fore limb began by flexion of all joints and raising
the limbs above the ground due to the simultaneous action of the flexor
muscles (F). This flexion was accompanied by a forward acceleration of
the limb. Maximal flexion of the leg coincides with maximal ventroflexion
of the hand. For the hind limb, the knee was maximally flexed at take
off and was extended afterward (fig. 4, frame 10, 11 and 1 compared to
frames 2 and 3). The foot was elevated a little above the ground by a
moderate flexion of the hip joint and a large flexion of the ankle. The end
of the flexion subphase of the swing was difficult to specify. Considering
the locked extension of the knee at 180° as a criterion for the onset of the
extension subphase (El), the flexion of the hind limb lasted about 70% of
the swing phase. Extension of the fore limb was performed by extension
152
153
of all three main joints. Extension of the hind limb involved a stable ankle,
the maximal extension of the knee joint and some extension of the hip joint.
A rear view of the polar bear during fast walk (fig. 5) revealed that during
the swing phase the femur was endorotated moving the flexed knee inward
and the foot outward. Then the knee was extended and exorotation of the
femur moved the foot medially. The foot was then prepared to land with
its axis parallel to the body axis (fig. 5).
A front view of the polar bear (fig. 6) suggests that the humerus was
rotated inward at the end of the stance phase, the elbow being brought
laterally, the wrist outward and the fingers inward. This rotation continued
during the flexion subphase of the swing. A rolling up movement of the
hand associated with ventroflexion was observed. The extension of the
swing was characterized by protraction and outer rotation of the humerus,
resulting in limb adduction. Just before the touch down, the palmar surface
was oriented medially. Then, the hand contacted the ground with its outer
border and total contact of the palmar surface was achieved by outward
rotation of the wrist.
Asymmetrical gaits
Captivity was not a favourable condition to observe running polar bears.
In the wild, polar bears may gallop on any kind of substrate. When they
accelerated to jump over an obstacle, they used only one stride of gallop.
This gait followed a transverse sequence, with one diagonal pair of feet
moving almost synchronously, while the other diagonal pair moved inde-
pendently (fig. 7). A flight period, which occured after the stance of a fore
limb (the right for all the cycles studied), corresponded to a general flexion
(fig. 7, frames 17 and 18) of the four limbs, named flexed suspension by
DAGG & DE Vos (1968), crossed flight by GAMBARYAN
(1974), and gath-
ered suspension by HILDEBRAND, (1977). It occured at the end of the gallop
cycle, before the touch down of a hind limb (left in all cases) which began
the next cycle. This flight was very short (about 8% of the cycle studied).
In the observed transverse gallop of the polar bear, limbs succession was
caracterized by: left hind, right hind, left fore and right fore limbs, the
fore and hind leads being on the same side of the body. In the example
Fig. 4. Slow walk of the polar bear. A: lateral view of a sequence. The direction of the
arrows under the right fore and hind limbs indicates the stance (downward)
and the swing
(upward) phases. B: corresponding gait diagram. The stages of the progression (1 to 11)
are indicated on the diagram. LF, left fore limb; LH, left hind limb; RF, right fore limb;
RH, right hind limb; El, extension subphase of the swing; E2, yield period; E3, propulsion
subphase;
F, flexion
period of the swing; FE, full extension
during a preliminary subphase
of
the stance.
154
155
illustrated in fig. 7, the duty factor was 35, the time lag in the asynchronous
diagonal (LH-RF) represented 55% of the cycle and only 3.75% in the other
diagonal (RH-LF). The hind and the fore leads were 24.3 and 27% of the
cycle, respectively. The total hind and fore limb contact durations were
respectively 62.1 and 64.8% of the cycle.
No good lateral views of the animals during a gallop were available. On
the 3/4 views, only one side of the bear could be studied, RH for the hinds
limbs and RF for the fore limbs (the leading). The hind limb behaved as
usual: footfall with the knee flexed followed by flexion of the different
limb joints. E3, which approximately began when the hip passed straight
over the foot contact (fig. 7, frames 6 and 7), corresponded to extension
of the joints. This indicated participation of the hip, knee and ankle in the
propulsive action of the limb. The knee and ankle joints flexed during F
(fig. 7, frames 17 and 18) before extension during El (fig. 6, frames 19 and
20) contributing to an increase in stride length.
The fore limb was almost completely extended at touch down. E2 seemed
to be very short (fig. 7, frames 10 and 11) and E3 long (fig. 7, frames 12
to 16). The E3 subphase suggested a movement of the scapula creating
an extension of the shoulder joint. This movement was concomitant to a
maximal extension of the elbow and an extension of the wrist. The right
fore limb was the only limb which made contact during the last part of
the gallop cycle, before suspension (fig. 7A). The subphase E3 of the right
fore limb followed the synchronous propulsive action of the diagonal limbs
RH-LF. The action of this limb may increase the efficiency and regularity of
propulsion and also contribute to the stability of such large animals (fig. 7,
frames 14, 15 and 16).
The study of all the sequences of galloping showed a relation between the
duration of fore and hind limb contacts with speed. Whatever the velocity,
fore and hind contacts represented more or less the same percentage of
the cycle (fig. 8A). For low and medium velocities, the fore contact lasted
approximately 60% of the hind contact, indicating that the leading limb
was only briefly in contact with the ground. At higher velocities, the fore
contact lasted 140% of the hind contact, indicating a relative lengthening of
the time the leading limb is in contact with the ground. In these gallops, the
unsupported interval in gathered position was always short and represented
between 0 and 20% of the cycle duration (fig. 8B). Sometimes there was
no unsupported period and the gathered limb position coincided with the
contact of one or two limbs, as is generally the case for heavy animals with
Fig. 5. Rear view of a sequence of slow walk of the polar bear (12 frames). The direction
of the arrows under the feet indicates the stance (downward)
and the swing (upward) phases.
White arrows: right foot, black arrows: left foot.
156
157
a limited flexibility of the vertebral axis (HILDEBRAND, 1977). The hind
and fore leads tended to increase when the duty factor decreased for each
limb, in relation with the increasing speed (fig. 8C).
Structure of the contact areas and function
The polar bear has a plantigrade stance. Studies of the hand and foot of a
cadaver and of plaster casts of palmar and plantar surfaces provided informa-
tion on their structure (snowshoe-shaped, alternation of different shapes).
The hand (fig. 9) showed two regions with resistant but elastic surfaces
formed by local thickening of the subepidermal tissues: dermal reticulum
and adipose panniculus. Proximally, a large semilunar pad was transversally
spread. Its inner part (close to the first finger) was well developed, whereas
its outer part (towards the fifth finger) was narrower. Within this large pad
five separate but confluent pads could be distinguished separated by weak
depressions. Distally, a second area corresponded to the line of five digital
pads. Digital and palmar pads were separated by a deep depression occu-
pied by a short thick brush-like fur. Proximal to the palmar pad, hairs were
radially set from a central pole, the shortest oriented forward covering the
posterior margin of the palmar pad. Very long hairs constituted a crown
around the hand, increasing the contact area with the ground. They passed
between the digital pads, covering their inner and outer margins. The skin
linked the fingers along half of their length forming a web under these hairs.
The hand did not possess carpal pads. The sole of the foot was longer and
narrower (W/L = 0.05) than the sole of the hand. The foot was di-
vided into six regions: 3 lines of pads and 3 fur areas. The first proximally
located pad was ovoid and corresponded to the heel. The second was a large
plantar semilunar pad, transversally spread, formed by five fused units. Its
outer part (fifth toe) was better developed than its inner part (first toe). The
third region was formed by a line of five digital pads. A triangular area of
short thick brush-like hairs separated the heel and the plantar pads. A deep
depression occupied by long hairs separated the plantar and the digital pads.
Long hairs constitute a crown around the foot sole surface. The surface of
the foot and hand pads has a granular appearance due to the outgrowth of
the outermost keratinized epidermal cells.
The footprints of palmar and plantar soles showed the same features on
any substrate. The prints of the palmar pad of the hand, and the short hairs
on its outline, suggest that this pad exerted the main contact during the
Fig. 6. Front view of a sequence
of slow walk of the polar bear ( 10
frames). The direction of
the arrows under the hands indicates the stance (downward)
and the swing (upward) phases.
White arrows: left hand, black arrows: right hand.
158
159
first footfall. The digital pads were also well delimited, except for the first
finger, which was not always visible. The fur located behind the palmar
pad, first contacting the ground, showed a circular print. This print, visible
during a slow walk, changed in shape during a fast walk and included the
region directly behind the palmar pad. The dense fur between the digital
and palmar pads was saturated with paint. Streams of paint oriented in the
direction of the movement were visible between the digital pads. Other
prints revealed a draining of the liquid by the long peripheral hairs towards
the body axis. The prints of the hind paw showed differences on four points.
The posterior part of the sole always indicated a heel contact area that was
larger than the area of the pad and which included the medial area of short
hairs. The metatarsal pads constituting the plantar pad showed five distinct
centers of pressure. The area between the plantar pad and the heel acted as
a sponge saturated with paint. The liquid was drained mainly in a backward
direction by the long peripheral hairs.
Comparison with brown bears
A comparison with the gallop of the brown bear (GAMBARYAN, 1974) was
made by aligning similar kinetic events during a cycle of both species
(fig. 10). The brown bear has a rotary gallop, with the fore and hind leads
on opposite sides (LH, RH, RF, LF). As in the polar bear, the gathered
suspension was produced by the thrust on the fore limbs. The flight starts
after the left fore limb stance for the brown bear, but after the right fore
limb stance for the polar bear. The two diagonals of the brown bear were
separated, while they were more synchronous in the polar bear. The fore
limb stride was longer than the hind limb stride in the brown bear.
There are marked differences between the foot pads of both species. Com-
pared with the plantar and palmar soles of the polar bear (fig. 11 ) the pads
of the brown bear were larger and the hairy regions were reduced: carpal
pads were present and on the foot, the plantar pad was much larger. Unlike
polar bears, the claws of the brown bear are in contact with the ground.
The hand prints of the brown bear suggested that the main contact was
provided by the palmar and the digital pads, because their surface was
Fig. 7. Gallop cycle of polar bear. A: 3/4 view
of a gallop
cycle of a polar bear. The direction
of the arrows under the feet and hands indicates the beginning
of the stance (downward)
and
the swing (upward) phases. B: succession of the limbs touch down indicated by the numbers
1, 2, 3 and 4. C: corresponding gait diagram. The stages of the progression (1 to 20)
are indicated on the diagram and correspond to the frames of the sequence (1 frame =
0.04 s). El, extension subphase of the swing; E2, yield period; E3, propulsion subphase;
F, flexion
period of the swing; FE, full extension
during a preliminary subphase
of the stance;
LF, left fore limb; LH, left hind limb; RF, right fore limb; RH, right hind limb.
160
161
immediately dry after contact. The outer carpal pad print (toward finger V)
was present in a slow walk but missing in a faster walk. The liquid was
drained by the surface structure of the pads as soon as they were pressed
against the ground for the first time. The hairs between the digital and
the palmar pads also assisted draining. Tracks made by the claws become
visible after several locomotor cycles. The large and bare plantar sole of
the foot, which is crossed by a transverse groove, gave a more limited print
which corresponded to the plantar pad, the posterior part of the heel and a
strip on the outer side of the foot. The digital pads and the claw contacts
were visible. Liquid was drained by the polygonal network of epidermal
cells on the pads surface. The pressure exerted on these pads drove the
liquid toward the less protuding regions where hairs were concentrated.
DISCUSSION
In the slow or the slow medium walk of the polar bear, which is charac-
terized by a lateral sequence (HILDEBRAND, 1966), the pendular action of
the limbs seems to be predominant. The propulsive action by the muscles
is probably weak. In this context, the flexion of the shoulder joint in E3
reveals the anticipated activity of the flexor muscles which normally act
only during the swing. The knee shows the same behaviour. The elbow
being locked in maximal extension during E3, the propulsive action of the
fore limb is generated by the wrist and the hand. In contrast, the hip and
.the ankle both play this role for the hind limb. One of the main features
of the symmetrical gaits is the presence of a subphase FE, corresponding
to the setting of the limb in a pre-strain condition, in particular the hind
limb which must support a large percentage of the body mass. Maximally
extended, the leg forms a column which is able to resist the mass transfered
on it, at the beginning of the contralateral limb swing phase. The direction
of the ground reaction force is probably subvertical. The stiff and extended
hind leg in subphase FE results in a walk with swaying hips.
Fig. 8. Variation of several parameters of the asymmetrical gaits of the polar bear'(from
HILDEBRAND,
1977). A: duration of fore and hind contact intervals as percent of the stride
interval. B: Gait graph relating hind support to midtime lag. The point surrounded by a
circle corresponds to the gallop presented in fig. 7. C: hind and fore leads relation to stance
phase (duty factor). Regression
is calculated
by means of least squares.
162
. , - - -
Fig. 9. Ventral
aspect of the right hand and foot of the polar bear and their footprints during
slow walk. I, II, III, IV and V, digits of the hand and the foot. A: right hand, d.p., digital
pads; h., hairy regions between the palmar and digital pads and behind the palmar pad; p.p.,
palmar pad. B: right foot, d.p., digital pads; h., pad of the heel; Ih., long hairs between
plantar and digital pads; Ish., longest hairs of the periphery; pl.p., plantar pad; sh., short hairs
between the heel and the plantar pad. C: right front leg footprint,
D: right hind leg footprint.
163
Fig. 10. Gallop cycle of a brown bear (Gambaryan, 1974). A: lateral view. The direction
of the arrows under the feet and hands, associated with LH, RH, LH and RF, indicates the
beginning of the stance (downward) and the swing (upward) phases. B: succession of the
limbs touch down. The succession of the limbs touch down is indicated by the numbers 1,
2, 3 and 4. C: gait diagram (20 stages). The stages of the progression
(1 to 20) are indicated
on the diagram and correspond to the frames of the sequence (1 frame = 0.04 s). On the
diagram of gait, the black lines and the dotted lines respectively represent the stance and the
swing phases. LF, left fore limb; LH, left hind limb; RH, right fore limb; RH, right hind
limb.
164
165
During the asymmetrical gaits, the propulsive activity of the hind limb
seems to increase, as demonstrated by the extension of all joints in E3.
The fore limb action is also amplified, and plays an important role in the
forward traction of the body. The shoulder musculature seems to mainly
operate in this way, assisted by the elbow. Both hind limbs probably have
the same propulsive effect. However, the leading fore limb seems to have a
greater propulsive action than the trailing limb. It is the only leg in contact
with the ground during the E3 subphase supporting the entire body mass,
just before the gathered suspension.
The transverse gallop used by the polar bear improves stability by increas-
ing the triangle of support, while the rotary gallop of the brown bear seems
more suited for manoeuvrability and climbing by the action of contralateral
limbs. GAMBARYAN
(1974) related the larger stride length of the fore limb
of brown bears to climbing. The difference in gallop may also be related
to geometrical features: the body of the polar bear is more elevated and the
limbs tend to have equal length.
Our experiments and observations at the Zoo revealed that the behaviour
of the brown bear was quite different from that of the polar bear when the
animals were faced with a slippery substrate. Brown bears were reluctant
to walk on perspex sheets and they slided on them. The polar bears has no
difficulty with walking on perpex and left footprints which were identical
to those on rough paper. This behavioural difference may be explained by
the increase of hairy areas in the polar bear, which improve grip on the
substrate.
CONCLUSION
The ability of the polar bear to travel at different gaits on ice and frozen
snow are probably the result of adaptive features at different structural levels.
The first level corresponds to the general aspect of the organism. The huge
body has a long trunk set above the ground by stiff limbs. The second level
concerns the use of the legs. The peculiar yield system contributes to a firm
grip on the slippery surface. At the end of the swing phase, the limb is
moved downward vertically forming a column by full extension of the joints.
This is a preparation for the transfer of a large part of the body mass before
the take-off of the contralateral limb occurs (subphase FE of the stance).
Fig. 11. Ventral aspect of the right hand and foot of a brown bear (Pocock, 1914) and their
footprints. A: right hand: c.p., carpal pads; d.p., digital pads; h., hairy; p.p. palmar pad.
B: right foot: d.p., digital pads; pl.p., plantar sole; h., hairy zone. C: right front leg footprint.
D: right hind leg footprint.
166
This loading results in some flexion of the leg (subphase E2 of cycle) which
is stopped by the activity of the extensor muscles (GOSLOW et al., 1973,
ORSAL, 1987). The FE strategy not only resists the mass transfered on a
leg, but probably favours a large contact of feet and hands with the ground
at the begining of E2. The third level is related to the structures for contact.
Plantigrady, including the contribution of the inner margin of the soles,
increases the surface supporting the body. The phalanges, particularly the
first, are laid flat on the ground as are the tarsal or the carpal, the metatarsal
or the metacarpal elements. Alternation of pads and hairy zones is a basic
characteristic of the plantar and palmar soles. The pads are orientated
perpendicular to the axis of the sole and to the direction of motion. There
are three hairy zones: short hairs are located posterior to the large pads
(palmar or plantar), long hairs occupy the area between the large pads and
the digital pads, and the longest hairs on the outer borders constitute a fold,
which increases the snowshoe-like surface of the feet. The structure of the
soles in polar bears creates an increase of the friction between the animal
and the substrate. This feature allows a good exchange of forces and avoids
aquaplanning and thus preserves the propulsive component.
The adaptation of the polar bear to travel on ice is probably the fitting
of the different structural systems acting at these three distinct levels of the
organism.
ACKNOWLEDGEMENTS
We are grateful to Mr J.J. Petter and Mme Leclerc-Cassan, who authorized
the experiments with thc polar and the brown bears in the zoo of Vincennes
(National Museum of Natural History) and also Mr R. Marion for the loan
of many video records and also for helpful information collected during ex-
peditions to the polar regions. Financial support was provided by a contract
between the Museum of Natural History and the Michelin Company.
REFERENCES
DAGG, A.I., 1973. Gaits in mammals. Mammal Rev. 3,4: 135-154.
DAGG,
A.I. & A. DE VOS,
1968. The walking gaits of some species of Pecora. J. Zool. Lond.
155: 103-110.
FISCHER, M.S., 1992. Kinematics of the locomotion of the hyrax and morphological adapta-
tions. A new approach to the locomotion
of smaller mammals. Am. J. Phys. Anthrop.
14: 75-86.
GAMBARYAN, P., 1974. How mammals run. Wiley, New York
(Orig. publ. in Russian, 1972).
GOSLOW,
G.E. JR.,
R.M. REINKING
& D.G. STUART,
1973. The cat step cycle: hind limb
joint
angles and muscle lengths during a restraining locomotion. J. Morph. 141: 1-42.
HARINGTON, C.R., 1970. Polar bear. Canadian Wildlife Service: Hinterland Who's Who.
167
HILDEBRAND, M., 1962. Walking, running and jumping. Am. Zool. 2: 151-155.
HILDEBRAND, M., 1966. Analysis of the symmetrical gaits of tetrapods. Folia Biotheoretica
6: 9-22.
HILDEBRAND, M., 1976. Analysis of tetrapod gaits: general considerations and symmetrical
gaits. In: R.M. Herman et al. (Eds): Advances in Behavioral Biology:
203-236. Plenum
Press, New York.
HILDEBRAND,
M., 1977. Analysis of asymmetrical
gaits. J. Mammal. 58: 131-156.
JENKINS,
F.A. JR., 1971. Limb posture and locomotion in the Virginia opossum (Didelphis
marsupialis) and in other non-cursorial mammals. J. Zool. Lond. 165: 303-315.
ORSAL, D., 1987. Analyse des coordinations intra et inter-appendiculaires
au cours de
l'activité locomotrice
chez le chat thalamique.
Thèse de doctorat d'Etat, univ Paris.
POCOCK, R.I., 1914. On the feet and other external features of the Canidae and Ursidae.
Proc.
Zool. Soc. Lond. 2: 913-941.
ROCHA-BARBOSA, O., S. RENOUS & J.P. GASC,
1996. Comparison of the fore and hind
limbs kinematics
in the symmetrical
and asymmetrical gaits of a caviomorph
rodent, the
domestic guinea pig, Cavia
porcellus (Linné, 1758) (Rodentia, Caviidae).
Ann. Sci. Nat.
(Zool.) 17 (4): 149-165.
ROCHA-BARBOSA, O., S. RENOUS & J.P. GASC,
1996.
Adaptation
à la course chez le cobaye
Cavia porcellus (Mammifère, Rongeur, Caviomorphe).
Bull. Soc. Zool. Fr. 121 (1):
121-123.
... Although polar bears and brown bears are both terrestrial, there are morphological differences on their paws related to their different habitat and terrain [32]. Polar bears adapted to live on the Arctic sea ice [32] and correspondingly have smaller paw pads with greater fur coverage on the paws [37] and short, sharp claws [29,38]. Decreased paw pad size in exchange for furred areas decreases the amount of heat loss in their cold habitats [37], and is also observed in other snow-dwelling animals [39][40][41][42][43]. ...
... In addition to thermal stability, paw fur will probably differentially influence traction on different substrates, yet this effect has not been studied. Although polar bear claws are shorter and more curved than those of brown bears, polar bear paw prints rarely show claw marks [29,38], suggesting that they do not generally rely on their claws to provide grip on snow. ...
... Brown bears and polar bears have the same energetic cost of locomotion on a treadmill [44], but no studies have quantitatively compared their efficiency on different substrates. In a qualitative observational study, polar bears walked easily on a slippery polymer surface, while brown bears were hesitant to attempt to walk on it [38]. Additionally, polar bears left the same footprints on the slippery and natural surfaces [38]. ...
Article
Full-text available
Microscopic papillae on polar bear paw pads are considered adaptations for increased friction on ice/snow, yet this assertion is based on a single study of one species. The lack of comparative data from species that exploit different habitats renders the ecomorphological associations of papillae unclear. Here, we quantify the surface roughness of the paw pads of four species of bear over five orders of magnitude by calculating their surface roughness power spectral density. We find that interspecific variation in papillae base diameter can be explained by paw pad width, but that polar bear paw pads have 1.5 times taller papillae and 1.3 times more true surface area than paw pads of the American black bear and brown bear. Based on friction experiments with three-dimensional printed model surfaces and snow, we conclude that these factors increase the frictional shear stress of the polar bear paw pad on snow by a factor of 1.3-1.5 compared with the other species. Absolute frictional forces, however, are estimated to be similar among species once paw pad area is accounted for, suggesting that taller papillae may compensate for frictional losses resulting from the relatively smaller paw pads of polar bears compared with their close relatives.
... Rotary gallops, as described above for the lateral walk, and transverse gallops, with the leading hindfoot placement being followed by the contralateral forefoot, can both be observed in the same species (Vilensky and Larson, 1989; Walter and Carrier, 2007), although there may be energetic differences between them (Bertram and Gutmann, 2009). Gallops are the fastest gait used by quadrupedal animals and studies have demonstrated that galloping occurs in species representing all three foot postures – unguligrade, digitigrade and bears within plantigrade species (Hildebrand, 1989; Renous et al., 1998; Robilliard et al., 2007; Walter and Carrier, 2007). Within carnivorans, bears are the most plantigrade along the posture continuum (Ginsburg, 1961). ...
... There has been very limited research into the locomotion and biomechanics of Ursidae (Gambaryan, 1974; Inuzuka, 1996; Renous et al., 1998); however, it is likely that differences in limb morphology and locomotor behaviour may exist within Ursidae (Irschick and Garland, 2001), as well as between bears and other quadrupeds. Previous studies have shown that locomotion by cursorial animals over a large size range can be described as dynamically similar across all speeds (Farley et al., 1993; Alexander, 2005). ...
Article
Full-text available
Locomotion of plantigrade generalists has been relatively little studied compared to more specialised postures even though plantigrady is ancestral among quadrupeds. Bears (Ursidae) are a representative family for plantigrade carnivorans, they have the majority of the morphological characteristics identified for plantigrade species, and they have the full range of generalist behaviours. This study compares the locomotion of adult grizzly bears (Ursus arctos horribilis Linnaeus 1758), including stride parameters, gaits and analysis of three dimensional ground reaction forces, to previously studied quadrupeds. At slow to moderate speeds grizzly bears use walks, running walks, and canters. Vertical ground reaction forces demonstrated the typical M-shaped curve for walks, however this was significantly more pronounced in the hind limb. The rate of force development was also significantly higher for the hind than the forelimbs at all speeds. Mediolateral forces were significantly higher than would be expected for a large erect mammal, almost to the extent of a sprawling crocodilian. There may be morphological or energetic explanations for the use of the running walk rather than the trot. The high medial forces (produced from a lateral push by the animal) could be caused by frontal plane movement of the carpus and elbow by bears. Overall, while grizzly bears share some similarities with large cursorial species, their locomotor kinetics have unique characteristics. Additional studies are needed to determine if these characters are a feature of all bears or plantigrade species. © 2015. Published by The Company of Biologists Ltd.
... Despite the paraphyletic relationship between polar bears and grizzly bears (Ursus arctos) (Talbot and Shields, 1996), polar bears exhibit a number of physiological and behavioral adaptations distinct from grizzly bears, likely as a consequence of their marine existence. In addition to being the most carnivorous of the bear species (Stirling and Derocher, 1990), polar bears have larger paws ( potentially as an adaptation for swimming; DeMaster and Stirling, 1981), reduced forelimb dexterity (Iwaniuk et al., 2000) and exhibit distinct running kinematics using a transverse gallop compared with the rotary gallop of grizzly bears (Renous et al., 1988). Additionally, a study using tri-axial accelerometers to test the ability of data from grizzly bears to serve as proxies for discriminating basic behaviors in polar bears found that data from grizzly bears failed to reliably discriminate polar bear behaviors (Pagano et al., 2017). ...
Article
Full-text available
Ursids are the largest mammals to retain a plantigrade posture. This primitive posture has been proposed to result in reduced locomotor speed and economy relative to digitigrade and unguligrade species, particularly at high speeds. Previous energetics research on polar bears (Ursus maritimus) found locomotor costs were more than double predictions for similarly sized quadrupedal mammals, which could be a result of their plantigrade posture or due to adaptations to their Arctic marine existence. To evaluate whether polar bears are representative of terrestrial ursids or distinctly uneconomical walkers, this study measured the mass-specific metabolism, overall dynamic body acceleration, and gait kinematics of polar bears and grizzly bears (Ursus arctos) trained to rest and walk on a treadmill. At routine walking speeds, we found polar bears and grizzly bears exhibited similar costs of locomotion and gait kinematics, but differing measures of overall dynamic body acceleration. Minimum cost of transport while walking in the two species (2.21 J kg-1 m-1) was comparable to predictions for similarly sized quadrupedal mammals, but these costs doubled (4.42 J kg-1 m-1) at speeds ≥5.4 km h-1 Similar to humans, another large plantigrade mammal, bears appear to exhibit a greater economy while moving at slow speeds.
... Bears can adopt a temporary upright posture but no study documenting their gait angle is known to the authors. For comparison, some estimates of the angle of gait during quadrupedal locomotion in the hind limb of a polar bear is 32° (Renous et al., 1998) and for the elephant is 22° (Demathieu, 1986) or 36° (Muybridge, 1899). These gait angles may be considered as the maximum value if these extant animals adopted an upright posture. ...
Article
Fossil footprints of ground sloths are mostly restricted to the late Miocene to Pleistocene of South America. This study is focused on the oldest known ground sloth trackways, Megatherichnum oportoi Casamiquela, 1974 from the late Miocene Río Negro Formation of northern Patagonia. The section logged at the study site, near Carmen de Patagones (Buenos Aires province), includes the uppermost part of the middle member (marine) and the upper member (aeolian) of the Río Negro Formation. Identified sedimentary facies can be grouped into four facies associations: tidal flat, aeolian dune, dry/damp interdune and wet interdune (shallow lacustrine). M. oportoi trackways are preserved in an upper intertidal mixed flat. Associated trace fossils belong to a wet aeolian system developed close to the sea coast and were mostly preserved in interdune facies. These include Poaceae root and stem traces and Nagtuichnus meuleni (Chlamyphorinae burrow) in dry interdune facies, indeterminate tetrapod footprints in damp interdune facies, Lockeia siliquaria and chevron-like trace fossils (bivalve resting and horizontal locomotion traces) in wet interdune facies (shallow lakes), and Palaeophycus tubularis in aeolian dune facies. The most likely trackmaker of M. oportoi is Pyramiodontherium sp. (Megatheriinae), recorded from the same stratigraphic unit at Chubut province, with a body mass ranging from 2.5 to 3.6 tonnes. M. oportoi is interpreted as a quadrupedal trackway of a late Miocene ground sloth without overlap of the pes on the manus. The previously proposed bipedal interpretation for the trackway requires angles of gait in excess of those permitted for such a large and heavy animal. Pleistocene ground sloth trackways are distinctive because of the much smaller size of the fore footprint. For the latter examples, a quadrupedal locomotion with overlap of the pes on the manus may be applied.
... Unlike other ursids, the polar bear is almost entirely carnivorous and ranges over tundra regions. To move efficiently over large distances in search of prey (up to 300 km per season; Stirling et al. 1978; Schweinsburg and Lee 1982), the polar bear also possesses a suite of morphological and behavioural adaptations that set it apart from its closest relatives, such as longer, stiffer limbs, a longer trunk, and dense mats of fur covering the paws (Renous et al. 1998). This strong reliance upon efficient locomotion appears to have been at the expense of forelimb dexterity, as the polar bear possesses significantly lower dexterity scores than other bears. ...
Article
Full-text available
Using a new rating scale of forelimb dexterity that separates the contribution of proximal components (shoulder, upper forelimb, and lower forelimb) from distal components (forepaw), we examined the relationship between functional demands and phylogeny and forelimb dexterity in 45 species of fissiped carnivores (Carnivora). Specifically, we examined the effects of body size, phylogenetic relatedness, diet (vertebrate predation), and locomotion (arboreality) on the differential evolution of forelimb dexterity. Regression analyses indicate that, although body size does appear to be positively correlated with the dexterity of the proximal components, the inclusion of phylogenetic information results in a nonsignificant relationship. Phylogenetic relatedness was found to account for a significant amount of interspecific variation in proximal, distal, and total (proximal + distal) dexterity. When phylogenetic effects were incorporated, arboreality was not significantly correlated with any of the dexterity scores, but vertebrate predation was, albeit a negative correlation. The amount of variation in the dexterity of proximal and distal components did, however, differ in magnitude within each significant result. Thus, each component can be differentially affected by specific functional demands. By examining the significant associations with diet and phylogeny and mapping the dexterity scores onto the phylogeny, we also demonstrate that the ancestral degree of forelimb dexterity of both the caniform and feliform lineages was approximately equal to that of the average extant carnivore. Thus, forelimb dexterity has decreased or increased within particular lineages, with reductions or elaborations in some species resulting from the invasion of specific niches not occupied by congeners.
... Moreover, unlike coordination within pairs of limbs, PG and PL are very different for each gait (Tables·2 and 3). Indeed, the pairs of limbs are not in the same position on the anteroposterior axis, translating the ; 3 (Wetzel et al., 1975); 4 (Hildebrand, 1959); 5 ; 6 (Dunbar, 2004); 7 (Renous et al., 1998); 8 (Robilliard et al., 2007); 9 (Dagg, 1969); 10 (Hutchinson et al., 2006). spatial movement of the hind pair back a trunk length of the animal with respect to the spatial movement of the fore pair. ...
Article
Full-text available
Only a few studies on quadrupedal locomotion have investigated symmetrical and asymmetrical gaits in the same framework because the mechanisms underlying these two types of gait seem to be different and it took a long time to identify a common set of parameters for their simultaneous study. Moreover, despite the clear importance of the spatial dimension in animal locomotion, the relationship between temporal and spatial limb coordination has never been quantified before. We used anteroposterior sequence (APS) analysis to analyse 486 sequences from five malinois (Belgian shepherd) dogs moving at a large range of speeds (from 0.4 to 10.0 m s(-1)) to compare symmetrical and asymmetrical gaits through kinematic and limb coordination parameters. Considerable continuity was observed in cycle characteristics, from walk to rotary gallop, but at very high speeds an increase in swing duration reflected the use of sagittal flexibility of the vertebral axis to increase speed. This change occurred after the contribution of the increase in stride length had become the main element driving the increase in speed - i.e. when the dogs had adopted asymmetrical gaits. As the left and right limbs of a pair are linked to the same rigid structure, spatial coordination within pairs of limbs reflected the temporal coordination within pairs of limbs whatever the speed. By contrast, the relationship between the temporal and spatial coordination between pairs of limb was found to depend on speed and trunk length. For trot and rotary gallop, this relationship was thought also to depend on the additional action of trunk flexion and leg angle at footfall.
Article
Full-text available
Tri-axial accelerometers have been used to remotely identify the behaviors of a wide range of taxa. Assigning behaviors to accelerometer data often involves the use of captive animals or surrogate species, as accelerometer signatures are generally assumed to be similar to those of their wild counterparts. However, this has rarely been tested. Validated accelerometer data are needed for polar bears Ursus maritimus to understand how habitat conditions may influence behavior and energy demands. We used accelerometer and water conductivity data to remotely distinguish 10 polar bear behaviors. We calibrated accelerometer and conductivity data collected from collars with behaviors from video-recorded captive polar bears and brown bears U. arctos, and with video from camera collars deployed on free-ranging polar bears on the sea ice and on land. We used random forest models to predict behaviors and found strong ability to discriminate the most common wild polar bear behaviors using a combination of accelerometer and conductivity sensor data from captive or wild polar bears. In contrast, models using data from captive brown bears failed to reliably distinguish most active behaviors in wild polar bears. Our ability to discriminate behavior was greatest when species- and habitat-specific data from wild individuals were used to train models. Data from captive individuals may be suitable for calibrating accelerometers, but may provide reduced ability to discriminate some behaviors. The accelerometer calibrations developed here provide a method to quantify polar bear behaviors to evaluate the impacts of declines in Arctic sea ice.
Article
The morphological characteristics of the appendicular skeleton of 26 adult fisher and 55 adult marten were studied to determine those characteristics that could be used to distinguish between species and sexes. Measurements and illustrations were used to supplement the descriptions of most bones. The appendicular skeletons of marten and fisher are similar in structure but it is possible to distinguish between the skeletal elements of these mustelids using morphometric data. Distinction can also be made between certain postcranial skeletal remains of males and females within each species using bone measurements.
Article
Full-text available
Certains Rongeurs de la lignée des Caviomorphes, tels que les Dasyproctidés et les Agoutidés, montrent des convergences avec quelques Artiodactyles africains appartenant aux Tragulidés et aux Bovidés.
Article
Asymmetrical gaits (that is, gallops and bounds) have the footfalls of a pair of feet unevenly spaced in time. Such gaits were studied from slow motion film for 79 genera. All information about the timing of events at the ground can be expressed by five variables. Foot contact intervals range from 16 to 70 percent of the cycle. Fore and hind contacts are nearly equal for most ungulates and carnivores; fore contacts are the shorter for most rodents and rabbits. Fore contacts are proportionately shorter at higher speeds. The size of the fore lead is less than the hind for some apes; fore and hind leads are about equal for many carnivores and ungulates; fore leads are the longer for most mammals-particularly for smaller, more agile genera when moving fast. Actions of the forefeet as a pair are related to those of the hind feet by “midtime lag.” When this variable is plotted against the percentage duration of ground contact by one or both hind feet, a basic gait graph is derived on which are distinguished gaits with no suspensions, with a gathered suspension, an extended suspension, and both suspensions. The distribution of plots on the graph also correlates roughly with body size, maneuverability, and lead sequence (that is, transverse, rotary, half bound, or bound). A terminology of asymmetrical gaits is presented. The distribution on the graph of 104 identified footfall formulas is shown, and formulas characteristic of 55 genera are depicted. Asymmetrical gaits probably evolved, in amphibians and several times in reptiles, to benefit escape. Gaits with short leads or none, and an extended suspension are considered primitive. All lead sequences evolved early.
Article
The relative timing of the cyclic contacts that the feet of tetrapods make with the ground in terrestrial locomotion determines the gaits of the animals. This chapter reports on a comprehensive and integrative study that establishes a system for analyzing gaits. The model facilitates description, identifies all possible gaits, permits the simultaneous study of hundreds of locomotor performances, and helps to interpret the selection of gaits by the various animals.
Article
Past studies of mammalian posture and locomotion have been made principally on cursorial species and current concepts are stereotyped accordingly. Mammalian limbs are usually characterized in terms of vertical orientation and parasagittal excursion; the assumption prevails that this type of stance and limb movement is typical of the class. In the present study, walking movements in eight mammalian species (Tachyglossus aculeatus, Didelphis marsupialis, Tupaia glis. Mesocricetus auratus, Rattus norvegicus, Mustela putorius, Heterohyrax brucei, and Felis domestica) were studied cineradiographically with particular attention given to limb posture and excursion relative to the parasagittal and horizontal planes. Only the cat and, to a lesser degree, the hyrax conform to the postural and locomotory pattern that has been regarded as characteristic of most terrestrial, quadrupedal mammals. In the other six species, the humeri and femora usually function in positions more horizontal than vertical and at angles oblique to the parasagittal plane. Furthermore, the excursion pattern of these species have interspecific differences; some patterns are more variable than others. The classical conception of “mammalian posture” and “mammalian locomotion” is inaccurate both as a description of the features possessed in common by living terrestrial mammals and as a hypothetical approximation of the condition in ancestral mammals. At present, non-cursorial mammals such as the opossum and tree shrew are more realistic models on which to base deductions concerning posture and locomotion in eatly mammals.
Article
A cinematographic analysis of the unrestrained walking, trotting, galloping, jumping and landing movements of 11 adult cats was undertaken to provide previously unavailable information concerning the demands imposed on the nervous system for the control of low and high speed movements and the demands imposed by such natural movements on muscle performance and proprioceptive response. With due regard for the swing (F and E1) and stance (E2 and E3) phases of the step cycle of an individual limb, single frame analysis of the film permitted measurement of instantaneous angles of the lower spine, hip, knee, ankle and metatarsophalangeal joints. Appropriate lever arm measurements were also made on 50 freshly dispatched cats and 25 cadavers such that the Law of Cosines could be used to calculate instantaneous lengths of select hind limb muscles that would apply to the natural movements of adult cats of small (1.5–2.5 Kg), intermediate (2.6–3.5 Kg) and large (3.6–4.5 Kg) size. Muscle displacements were analyzed relative to maximum and minimus in situ lengths and the lengths associated with quiet standing. Use was also made of a previous electromyographic analysis of hind limb muscles during unrestrained locomotion (Engberg and Lundberg, '69). The sequential relations between the four phases of the step cycle are maintained as forward speed increases from walking ( < 2 mph) to high speed galloping ( > 16 mph). There are significant differences in the time consumed by each phase, however, with a greater reduction in the E3 phase, little reduction in the E2 and E1 phases and virtually no reduction in the F phase. When each phase is expressed as a relative percentage of the duration of the total step cycle, the greatest reduction is again in E3 with little change in the E2 phase. In contrast F and E1 phases increase in the percent of time they occur in each cycle, with the greatest increase in the F phase. For all speeds, analysis of the phase relations between movements of various sections of the hind limb revealed a remarkable unity of knee and ankle joint movement. The hip joint is largely out of phase with the knee and ankle during E1 and E2, all three joints being in phase in F and E3. The digits are essentially out of phase with the other joints except in the stance phase of the gallop. Rates and extents of muscle displacement during natural movements are greater than might be anticipated when expressed in absolute mm's and mm/sec but not when considered in relation to maximum and minimum in situ length and the length associated with quiet standing (Ls). During stepping a progressive increase in forward speed results in: (a) a greater usage of muscles at lengths between Ls and maximum in situ length; (b) for knee and ankle extensors, pronounced increase in the lengthening contraction associated with the E2 (yield) phase of step; and, (c) for both flexor and extensor muscles, an increased active phase of lengthening or near isometric contraction immediately prior to periods of active shortening. In contrast to these changes in active muscle status, the change from walking to galloping has little effect on the extent and rate of passive muscle displacements, particularly the F phase stretch of extensors. For the soleus muscle, calculations were made of the relation between changes in overall muscle length during natural movements and the length of the average muscle fiber and the tendon of insertion. These measurements revealed that the increases in fiber length when passive and decreases in length during active shortening are less than would be anticipated from the extensive liteature on extirpated fibers. In contrast, the increase in fiber length when active is greater than would be expected from the admittedly sparse literature on this subject. The results of this study are discussed largely in relation to two points of neurophysiological interest: the physiological range of muscle stretch as it pertains to the responsiveness of muscle spindles and tendon organs; and those mechanical aspects of lengthening contractions that give insight into the neural control of stepping. For exciting both spindles and tendon organs passive muscle stretch and shortening contractions are shown to be relatively ineffective and lengthening and isometric contractions particularly effective movements. It is suggested that, just as recent literature has emphasized the co-activation of efferent alpha and gamma motoneurons as a muscle becomes active, so too is there a synchronous activation of afferents, particularly the Ia and group II endings of muscle spindles and Ib endings of tendon organs. Finally the thesis is advanced that, while it has been convenient to separate E2 from E3 in the description of the stance phase of the step cycle, extensor muscles are actually undergoing a single mechanical event: an active stretch-shorten cycle for knee and ankle extensors and an active isometric-shorten cycle for hip extensors. This hypothesis has significant implications for the neural control program that regulates the stepping sequence in that it emphasizes the extent to which appropriate changes must be preprogrammed in the mechanical properties of muscles for the smooth execution of stepping.
Kinematics of the locomotion of the hyrax and morphological adaptations. A new approach to the locomotion of smaller mammals
  • M S Fischer
FISCHER, M.S., 1992. Kinematics of the locomotion of the hyrax and morphological adaptations. A new approach to the locomotion of smaller mammals. Am. J. Phys. Anthrop. 14: 75-86.
Analyse des coordinations intra et inter-appendiculaires au cours de l'activité locomotrice chez le chat thalamique
  • D Orsal
  • Paris Etat
ORSAL, D., 1987. Analyse des coordinations intra et inter-appendiculaires au cours de l'activité locomotrice chez le chat thalamique. Thèse de doctorat d'Etat, univ Paris.