Martin S. Fischer

The locomotor kinematics of Asian and African elephants : changes with speed and size

SUMMARY For centuries, elephant locomotion has been a contentious and confusing challenge for locomotion scientists to understand, not only because of technical difficulties but also because elephant locomotion is in some ways atypical of more familiar quadrupedal gaits. We analyzed the locomotor kinematics of over 2400 strides from 14 African and 48 Asian elephant individuals (body mass 116-4632 kg) freely moving over ground at a 17-fold range of speeds, from slow walking at 0.40 m s-1 to the fastest reliably recorded speed for elephants, 6.8 m s-1. These data reveal that African and Asian elephants have some subtle differences in how size-independent kinematic parameters change with speed. Although elephants use a lateral sequence footfall pattern, like many other quadrupeds, they maintain this footfall pattern at all speeds, shifting toward a 25% phase offset between limbs (singlefoot) as they increase speed. The duty factors of elephants are greater for the forelimbs than for the hindlimbs, so an aerial phase for the hindquarters is reached at slower speeds than for the forequarters. This aerial phase occurs at a Froude number of around 1, matching theoretical predictions. At faster speeds, stance and swing phase durations approach asymptotes, with the duty factor beginning to level off, concurrent with an increase in limb compliance that likely keeps peak forces relatively low. This increase of limb compliance is reflected by increased compression of the hindlimbs. Like other tetrapods, smaller elephants are relatively more athletic than larger ones, but still move very similarly to adults even at <500 kg. At any particular speed they adopt greater relative stride frequencies and relative stride lengths compared to larger elephants. This extends to near-maximal locomotor performance as well - smaller elephants reach greater Froude numbers and smaller duty factors, hence likely reach relatively greater peak loads on their limbs and produce this force more rapidly. A variety of lines of kinematic evidence support the inference that elephants change their mechanics near a Froude number of 1 (if not at slower speeds), at least to using more compliant limbs, if not spring-like whole-body kinetics. In some ways, elephants move similarly to many other quadrupeds, such as increasing speed mainly by increasing stride frequency (except at fast speeds), and they match scaling predictions for many stride parameters. The main difference from most other animals is that elephants never change their footfall pattern to a gait that uses a whole-body aerial phase. Our large dataset establishes what the normal kinematics of elephant locomotion are, and can also be applied to identify gait abnormalities that may signal musculoskeletal pathologies, a matter of great importance to keepers of captive elephants.

Arboreal locomotion in rats – the challenge of maintaining stability

SUMMARY Arboreal locomotion has mainly been looked at to date in the context of investigations into the specialization of primates and other ‘arboreally adapted’ animals. The feat of moving on branches as small or smaller than the bodys diameter was tested in rats (Rattus norvegicus) as they moved on horizontal poles of different diameters. The data were compared with data pertaining to terrestrial locomotion. We investigated three-dimensional kinematics and dynamics using biplanar cineradiography with simultaneous substrate reaction force (SRF) measurements. As predicted, rats flexed fore- and hindlimbs and reduced vertical forces during pole locomotion. In addition, the orientation of the mediolateral substrate reaction force resultant (SRR) and impulses switched from lateral to medial. In order to maintain stability during arboreal locomotion, lateral spine movements increased. We propose that the combination of lateral sequence gaits, similar travel speed of the animals and similar contact times, higher or similar peak vertical forces as well as similar mediolateral impulses in forelimbs and hindlimbs are typical of clawed mammals moving on thin supports. Clawed mammals and primates share the reduction of vertical oscillations and side-to-side fluctuations, a crouched posture as well as the increase in lateral spine movements. We conclude that these features are behavioral adaptations caused by the biomechanical constraints of small branch locomotion, regardless of the way they make contact with the substrate.

Spatiotemporal surface EMG characteristics from rat triceps brachii muscle during treadmill locomotion indicate selective recruitment of functionally distinct muscle regions.

Abstract. Multichannel surface EMG recordings of a multiheaded skeletal muscle during cyclic locomotion combined with cineradiography were analysed in a chronic experiment. The resulting detailed two-dimensional activation pattern from the long and lateral triceps brachii heads of the rat during treadmill locomotion were combined with gait characteristics and fibre typing of the muscle. Shortly before ground contact of the forelimb, maximum muscle activity was found in the proximal part of the long head of the muscle. During the stance phase maximum activity was observed in the proximal part of the lateral head. The frequency dependent behaviour of cross-covariance functions over both muscle heads confirmed this selective shift in activation. In the lateral triceps brachii head of the investigated rats, exclusively type II fibres were found. In the long head the frequency of type I fibres was the highest in the deep muscle layers, proximally more than distally, whereas type II fibres were dominant in more superficial muscle layers. A combination of physiological and histological findings supports an anticipating mechanism whereby fine-tuning of the vertical foot down manoeuvre is mainly achieved by the (type I fibre dominated) proximal deep compartment of the biarticular long triceps brachii head and force generation is predominantly executed by the monoarticular lateral triceps brachii head.

Morphological Integration in Mammalian Limb Proportions: Dissociation between Function and Development

During mammalian evolution, fore- and hindlimbs underwent a fundamental reorganization in the transformation from the sprawled to the parasagittal condition. This caused a dissociation between serial and functional homologues. The mobilized scapula functions as the new proximal forelimb element and is functionally analogous to the femur of the hindlimb. Tarsus and metatarsus built a new functional hindlimb element that is functionally analogous to the forearm of the forelimb. Morphological covariation between serially homologous fore- and hindlimb elements can conflict with biomechanical demands when certain intralimb proportions are required for the postural stability of motion. The limb proportions of 189 mammalian species were examined to test whether intralimb proportions are governed by a general principle that corresponds to biomechanical predictions. Morphological covariation between functionally analogous and serially homologous fore- and hindlimb elements was tested by a correlation analysis. A clear relationship exists between the proportions of the first and the third elements of each limb, while the middle element is less involved in alterations of intralimb proportions. Hindlimb proportions are largely uniform across mammals and correspond to biomechanical predictions regarding postural stability. The greater variability in forelimb proportion is likely be the expression of various adaptations but might results also from constraints due to the shared developmental programs with the hindlimb.

Cineradiographic study of forelimb movements during quadrupedal walking in the brown lemur (Eulemur fulvus, primates: Lemuridae)

Movements of forelimb joints and segments during walking in the brown lemur (Eulemur fulvus) were analyzed using cineradiography (150 frames/sec). Metric gait parameters, forelimb kinematics, and intralimb coordination are described. Calculation of contribution of segment displacements to stance propulsion shows that scapular retroversion in a fulcrum near the vertebral border causes more than 60% of propulsion. The contribution by the shoulder joint is 30%, elbow joint 5%, and wrist joint 1%. Correlation analysis was applied to reveal the interdependency between metric and kinematic parameters. Only the effective angular movement of the elbow joint during stance is speed-dependent. Movements of all other forelimb joints and segments are independent of speed and influence, mainly, linear gait parameters (stride length, stance length). Perhaps the most important result is the hitherto unknown and unexpected degree of scapular mobility. Scapular movements consist of ante-/retroversion, adduction/abduction, and scapular rotation about the longitudinal axis. Inside rotation of the scapula (60 degrees -70 degrees ), together with flexion in the shoulder joint, mediates abduction of the humerus, which is not achieved in the shoulder joint, and is therefore strikingly different from humeral abduction in man. Movements of the shoulder joint are restricted to flexion and extension. At touch down, the shoulder joint of the brown lemur is more extended compared to that of other small mammals. The relatively long humerus and forearm, characteristic for primates, are thus effectively converted into stride length. Observed asymmetries in metric and kinematic behavior of the left and right forelimb are caused by an unequal lateral bending of the spinal column.

The kinematic consequences of locomotion on sloped arboreal substrates in a generalized (Rattus norvegicus) and a specialized (Sciurus vulgaris) rodent

SUMMARY Small mammals must negotiate terrains that consist of numerous substrates that vary in diameter, surface structure, rigidity and orientation. Most studies on mammals have focused on the effects of substrate diameter during horizontal locomotion, especially in small- to medium-sized primates and marsupials. Locomotion across sloped arboreal substrates, however, is poorly understood. Here, in order to determine which locomotor parameters a terrestrial mammal, the rat, and a tree-dwelling mammal, the European red squirrel, modify in response to differences in substrate orientation, three-dimensional kinematics were examined using biplanar videoradiography as the animals moved on 30 and 60 deg inclined branches. Our results revealed that to maintain stability and friction as well as balance during inclined branch locomotion, these species utilize comparable locomotor adjustments despite significant differences in travel speed and gait. Rats and European red squirrels increased limb flexion and retraction in order to bring the center of mass as close as possible to the substrate surface and to achieve maximum propulsion. Additionally, forelimbs were placed more laterally and underneath the branch whereas the hindlimbs were placed approximately on the top of the branch. These locomotor adjustments, which have also been observed in primates and marsupials, are independent of speed, morphological adaptations and limb proportions and thus might be strategies used by early mammals. Our results also suggest that mammals that lack, or have reduced, grasping abilities try to maintain the locomotor mode used during horizontal branch locomotion on inclined branches for as long as possible.

Kinematics and Center of Mass Mechanics During Terrestrial Locomotion in Northern Lapwings (Vanellus vanellus, Charadriiformes)

Avian bipedalism is best studied in derived walking/running specialists. Here, we use kinematics and center of mass (CoM) mechanical energy patterns to investigate gait transitions of lapwings-migratory birds that forage on the ground, and therefore may need a trade-off between the functional demands of terrestrial locomotion and long distance flights. The animals ran on a treadmill while high-speed X-ray videos were recorded within the sustainable speed range. Instantaneous CoM mechanics were computed from integrating kinematics and body segment properties. Lapwings exhibit similar locomotor characteristics to specialized walking/running birds, but have less distinct gaits. At slow speeds no clear separation between vaulting (i.e., walking) and bouncing (i.e., running) energy patterns exists. Mechanical energy recovery of non-bouncing gaits correlates poorly with speed and suggests inefficient use of the inverted pendulum mechanism. Speed ranges of gaits overlap considerably, especially those of grounded running, a gait with CoM mechanics indicative of running but without an aerial phase, and aerial phase running, with no preferential gait at most speeds. Compliant limb morphology and grounded running in birds can be regarded as an evolutionary constraint, but lapwings effectively make use of advantages offered by this gait for a great fraction of their speed range. Thus, effective usage of grounded running during terrestrial locomotion is suggested generally to be a part of striding avian bipedalism-even in species not specialized in walking/running locomotion.

Three-dimensional reconstruction of histological sections using modern product-design software

Computer‐based, three‐dimensional reconstruction of histological sections is necessary for solving a diversity of questions in morphology and anatomy. Programming software for this purpose is difficult and time‐consuming. Therefore, we tested if commercially available product‐design software is useful for reconstructing anatomical virtual models.

Comparative intralimb coordination in avian bipedal locomotion.

SUMMARY Analyses of how intralimb coordination during locomotion varies within and across different taxa are necessary for understanding the morphological and neurological basis for locomotion in general. Previous findings suggest that intralimb proportions are the major source of kinematic variation that governs intralimb coordination across taxa. Also, independence of kinematics from habitat preference and phylogenetic position has been suggested for mammals. This leads to the hypothesis that among equally sized bird species exhibiting equal limb proportions, similar kinematics can be observed. To test this hypothesis, the bipedal locomotion of two distantly related ground-dwelling bird species (Eudromia elegans and Coturnix coturnix) and of a less terrestrial species (Corvus monedula) was investigated by means of a biplanar high-speed X-ray videographic analysis. Birds exhibited similar intralimb proportions and were filmed over a broad range of speed while moving on a treadmill. Joint and limb element angles, as well as pelvic rotations, were quantified. Regarding fore–aft motions of the limb joints and elements, a congruent pattern of intralimb coordination was observed among all experimental species. The sample of species suggests that this is largely independent of their habitat preference and systematic position and seems to be related to demands for coping with an irregular terrain with a minimum of necessary control. Hence, the initial hypothesis was confirmed. However, this congruence is not found when looking at medio-lateral limb motions and pelvic rotations, showing distinct differences between ground-dwellers (e.g. largely restricted to a parasagittal plane) and C. monedula (e.g. increased mobility of the hip joint).

Functional morphology and three-dimensional kinematics of the thoraco-lumbar region of the spine of the two-toed sloth.

SUMMARY Given the importance of thoraco-lumbar spine movements in the locomotion of mammals, it is surprising that in vivo three-dimensional (3-D) data on the intervertebral movement of the mammalian thoraco-lumbar vertebral column during symmetrical gaits is limited to horses and dogs. To test whether kinematic patterns similar to those published for these cursorial species are also present during a contrasting mode of quadrupedalism, we quantified thoraco-lumbar intervertebral movements, the resulting pelvic displacements and relative femoral movements during the trot-like steady-state suspensory quadrupedal locomotion of the two-toed sloth (Xenarthra, Choloepus didactylus). Scientific rotoscoping, a new, non-invasive approach that combines synchronous biplanar high speed X-ray videos and the reconstruction of skeletal elements from computed tomography bone scans, was used to quantify 3-D kinematics. An analysis of vertebral anatomy and epaxial muscle topography suggests that the thoraco-lumbar spine of sloths is well suited to producing lateral bending and long-axis rotation, but limits powerful sagittal extension. Sloths exhibit complex 3-D movements in the thoraco-lumbar spine that are comparable to those observed in other arboreal quadrupedal mammals. Monophasic lateral bending and long-axis rotation, biphasic sagittal bending and maximal amplitude of sagittal bending at the lumbo-sacral joint were also found in other quadruped mammals and may represent general aspects of mammalian symmetric gaits. Maximal amplitude of lateral bending and long-axis rotation vary in regard to the vertebral level. It is suggested that a cranio-caudal pattern of angular deflections of the spine results from the out-of-phase movement of diagonal forelimbs and hindlimbs in other walking gaits, because it is not evident in the trot-like locomotion analyzed here. The analysis also illustrates the difficulties that arise when lumbar movement is deduced from intervertebral joint morphology alone.