Rémi Hackert

Steady locomotion in dogs: temporal and associated spatial coordination patterns and the effect of speed

SUMMARY 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.

Gait parameters of treadmill versus overground locomotion in mouse

Many studies of interest in motor behaviour and motor impairment in mice use equally treadmill or track as a routine test. However, the literature in mammals shows a wide difference of results between the kinematics of treadmill and overground locomotion. To study these discrepancies, we analyzed the locomotion of adult SWISS-OF1 mice over a large range of velocities using treadmill and overground track. The use of a high-speed video camera combined with cinefluoroscopic equipment allowed us to quantify in detail the various space and time parameters of limb kinematics. The results show that mice maintain the same gait pattern in both conditions. However, they also demonstrate that during treadmill exercise mice always exhibit higher stride frequency and consequently lower stride length. The relationship of the stance time and the swing time against the stride frequency are still the same in both conditions. We conclude that the conflict related to the discrepancy between the proprioceptive, vestibular, and visual inputs contribute to an increase in the stride frequency during the treadmill locomotion.

Bird terrestrial locomotion as revealed by 3D kinematics.

Most birds use at least two modes of locomotion: flying and walking (terrestrial locomotion). Whereas the wings and tail are used for flying, the legs are mainly used for walking. The role of other body segments remains, however, poorly understood. In this study, we examine the kinematics of the head, the trunk, and the legs during terrestrial locomotion in the quail (Coturnix coturnix). Despite the trunk representing about 70% of the total body mass, its function in locomotion has received little scientific interest to date. This prompted us to focus on its role in terrestrial locomotion. We used high-speed video fluoroscopic recordings of quails walking at voluntary speeds on a trackway. Dorso-ventral and lateral views of the motion of the skeletal elements were recorded successively and reconstructed in three dimensions using a novel method based on the temporal synchronisation of both views. An analysis of the trajectories of the body parts and their coordination showed that the trunk plays an important role during walking. Moreover, two sub-systems participate in the gait kinematics: (i) the integrated 3D motion of the trunk and thighs allows for the adjustment of the path of the centre of mass; (ii) the motion of distal limbs transforms the alternating forward motion of the feet into a continuous forward motion at the knee and thus assures propulsion. Finally, head bobbing appears qualitatively synchronised to the movements of the trunk. An important role for the thigh muscles in generating the 3D motion of the trunk is suggested by an analysis of the pelvic anatomy.

Experimental study of coordination patterns during unsteady locomotion in mammals

SUMMARY A framework to study interlimb coordination, which allowed the analysis of all the symmetrical and asymmetrical gaits, was recently proposed. It suggests that gait depends on a common basic pattern controlling the coordination of the forelimbs (fore lag, FL), the coordination of the hindlimbs (hind lag, HL) and the relationship between these two pairs of limbs (pair lag, PL) in an anteroposterior sequence of movement (APS). These three time parameters are sufficient for identifying all steady gaits. We assumed in this work that this same framework could also be used to study non-steady locomotion, particularly the transitions between symmetrical and asymmetrical gaits. Moreover, as the limbs are coordinated in time and also in space during locomotion, we associated three analogous space parameters (fore gap, FG; hind gap, HG and pair gap, PG) to the three time parameters. We studied the interlimb coordination of dogs and cats moving on a runway with a symmetrical gait. In the middle of the runway, the gait was disturbed by an obstacle, and the animal had to change to an asymmetrical coordination to get over it. The time (FL, HL, PL) and space (FG, HG, PG) parameters of each sequence of the trials were calculated. The results demonstrated that the APS method allows quantification of the interlimb coordination during the symmetrical and asymmetrical phases and during the transition between them, in both dogs and cats. The space and time parameters make it possible to link the timing and the spacing of the footfalls, and to quantify the spatiotemporal dimension of gaits in different mammals. The slight differences observed between dogs and cats could reflect their morphological differences. The APS method could thus be used to understand the implication of morphology in interlimb coordination. All these results are consistent with current knowledge in biomechanics and neurobiology, therefore the APS reflects the actual biological functioning of quadrupedal interlimb coordination.

Multi-channel EMG of the M. triceps brachii in rats during treadmill locomotion

OBJECTIVES The study aims at a precise characterisation of intramuscularly varying recruitment patterns within the triceps brachii muscle (long and lateral head; proximal, medial, distal regions) in the time course of averaged step cycles during locomotion. METHODS The triceps brachii muscle of 15 Hannover rats was investigated with a supramuscular 16-electrodes grid during treadmill locomotion. Multi-channel electromyogram (EMG) was recorded simultaneously with high-speed videography. The rectified and smoothed EMG was time-normalised. EMG profiles and dynamic EMG-map series were calculated. Differences between EMG distribution patterns were tested by multivariate analysis of variance. RESULTS In the pre-stance phase EMG activity increased especially in the proximal long head. It most likely propagated from lower muscle layers of the long head. During stance phase the EMG activity of the lateral head rose steeply and exceeded those of the long head in short time. The fastest steps show the highest EMG amplitudes. CONCLUSIONS EMG registrations with grid electrodes help in the identification of intramuscular co-ordination processes during locomotion. While the EMG profiles characterise the time course, the topographical distribution is better represented in dynamic EMG interference maps. The dynamic changing activation patterns of triceps brachii depend on the phase of the step cycle. This clearly indicates the different functions of the muscle heads.

Transfer of biological principles into the construction of quadruped walking machines

In the wide range of possible biological and technical solutions for legged terrestrial locomotion, quadrupeds represent a compromise between lightweight construction, dynamic stability, and usage of self-stabilizing effects and minimization of neural control. Several biomechanical features indicate that mammals form interesting and preferable paradigms for the construction of walking machines, even if their morphology and locomotory functions in some issues seem to be more complicated than that of the phylogenetically older amphibians and reptiles.

Biomimetic robotics should be based on functional morphology

Due to technological improvements made during the last decade, bipedal robots today present a surprisingly high level of humanoid skill. Autonomy, with respect to the processing of information, is realized to a relatively high degree. What is mainly lacking in robotics, moving from purely anthropomorphic robots to ‘anthropofunctional’ machines, is energetic autonomy. In a previously published analysis, we showed that closer attention to the functional morphology of human walking could give robotic engineers the experiences of an at least 6 Myr beta test period on minimization of power requirements for biped locomotion. From our point of view, there are two main features that facilitate sustained walking in modern humans. The first main feature is the existence of ‘energetically optimal velocities’ provided by the systematic use of various resonance mechanisms: (a) suspended pendula (involving arms as well as legs in the swing phase of the gait cycle) and matching of the pendular length of the upper and lower limbs; (b) inverted pendula (involving the legs in the stance phase), driven by torsional springs around the ankle joints; and (c) torsional springs in the trunk. The second main feature is compensation for undesirable torques induced by the inertial properties of the swinging extremities: (a) mass distribution in the trunk characterized by maximized mass moments of inertia; (b) lever arms of joint forces at the hip and shoulder, which are inversely proportional to their amplitude; and (c) twisting of the trunk, especially torsion. Our qualitative conclusions are three‐fold. (1) Human walking is an interplay between masses, gravity and elasticity, which is modulated by musculature. Rigid body mechanics is insufficient to describe human walking. Thus anthropomorphic robots completely following the rules of rigid body mechanics cannot be functionally humanoid. (2) Humans are vertebrates. Thus, anthropomorphic robots that do not use the trunk for purposes of motion are not truly humanoid. (3) The occurrence of a waist, especially characteristic of humans, implies the existence of rotations between the upper trunk (head, neck, pectoral girdle and thorax) and the lower trunk (pelvic girdle) via an elastic joint (spine, paravertebral and abdominal musculature). A torsional twist around longitudinal axes seems to be the most important.

Limb preference in the gallop of dogs and the half-bound of pikas on flat ground

During fast locomotion—gallop, half-bound, bound—of quadruped mammals, the ground contact of the limbs in each pair does not alternate symmetrically. Animals using such asymmetrical gait thus choose whether the left or the right limb will contact the ground first, and this gives rise to limb preference. Here, we report that dogs (Mammalia, Carnivora) and pikas (Mammalia, Lagomorpha) prefer one forelimb as trailing limb and use it as such almost twice as often as the other. We also show that this choice depends on the individual and is not a characteristic of the species, and that the strength of the preference was not dependent on the animals running speed.

Kinematic Modeling of Bird Locomotion from Experimental Data

We present the design of a bird-like kinematics model for a biped robot as an alternative to the human model. The starting point of the research consists of analyzing the walking motion of quail birds using biological data obtained by X-ray radiography. The 3-D-motion analysis allows identification of the number of degrees of freedom (DOF) and the rotation mechanism for each leg, especially the main rotation axis. Leg joints are located at the hip, knee, ankle, and foot. The ankle is off the ground. Using this analysis, we have designed a biped kinematics model with a minimum of actuated joints and with the original orientation of hip and ankle main rotary joints, which are not horizontally and vertically oriented as in classical biped robotics. Given a reference-foot trajectory, we carry out simulations to compare internal-joint trajectories with the ones obtained from biological measurements. We show that the proposed model can be used to reproduce the kinematics of bird locomotion with a minimum of four actuated joints per leg, i.e., two at the hip and one at the knee, and one at the ankle, which is less than the usual six joints per leg that drive anthropomorphic legs.

Interactions between Motions of the Trunk and the Angle of Attack of the Forelimbs in Synchronous Gaits of the Pika (Ochotona rufescens)

During half-bound gait on a treadmill pikas (Ochotona rufescens: Lagomorpha) show a preference in the choice of the trailing limb (“handedness”). Duration of steps shows significantly higher variation in the trailing limb than in the leading limb. This observation motivated calculations of the position of the center of mass (CoM) in the body frame of the pika during half-bound cycles. CoM is aligned with first of the ulna of the trailing and second of the leading limb during major parts of the forelimbs’ stance phase. Referring to our large cineradiographic data base on the kinematics of the legs we could note that the horizontal motion of the CoM in the body is mainly determined by flexion and extension of the back. This observation underlines the determinant role of the trunk as the main engine for fast locomotion. Using high-speed video films we measured the angle of attack (defined as the angle between the ulna and the ground at touch down). We couldn’t observe any significant change with speed during half-bound, indicating the important role of self-stabilising mechanisms on the choice of kinematics.