Diagonal Couplets Research Articles

A new method to calculate limb phase from trackways reveals gaits of sauropod dinosaurs

Limb phase, the timing of the footfalls in quadrupedal locomotion that describes common gaits such as the trot and the pace gait,1,2 is widely believed to be difficult or even impossible to estimate for extinct tetrapods.3-5 We here present a fundamentally new approach that allows for estimating limb phase based on variation patterns in long trackways. The approach is tested on trackways of modern mammals, where the estimates generally correspond well with the actually employed limb phase. We then estimate limb phases of giant wide-gauged sauropod dinosaurs based on three long trackways from the Lower Cretaceous of Arkansas, US.6,7 Gait selection at the largest body sizes is of considerable interest given the lack of modern analogs. Contrary to previous assumptions,8,9 our estimates suggest lateral sequence diagonal couplet walks, in which the footfalls of the diagonal limb pairs (e.g., right hind and left fore) are more closely related in time than those of the same side of the body (e.g., right hind and right fore). Such a gait selection allows for efficient walking while maintaining diagonal limb support throughout the step cycle, which is important for a giant, wide-gauged trackmaker.10 Estimations of limb phase may help to constrain other gait parameters, body size and shape, and, finally, potential trackmaker taxa.

Vertical locomotion in the arboreal salamander Aneides vagrans

AbstractSalamanders are often used as a model of early tetrapod locomotion, due to their generalized tetrapod body plan. We imaged five individuals of wandering salamander, Aneides vagrans, during horizontal and vertical locomotion and compared kinematic and gait adjustments made to compensate for each condition. We used ImageJ to calculate duty factor, stride length, stride frequency, contralateral foot spread, heading of climbing, and forward velocity. Like other terrestrial salamanders, A. vagrans use a diagonal couplet, lateral sequence walk on horizontal surfaces. When walking vertically, however, they use a single‐foot gait, taking smaller steps and extending the duty factor compared with level walking. Salamanders adjusted their limbs to have a wider contralateral foot spread between fore‐ and hindfeet when walking downward as compared to walking upward or horizontally. These gait adjustments may minimize the risk of slipping or falling by increasing the number of contact points during the stride cycle, and by bringing their center of mass closer to the surface. We found that salamanders moved at a significantly faster velocity when traveling horizontally compared to vertically. Furthermore, we found no significant difference between upward and downward velocity, despite greater stride lengths in upward locomotion; this was explained by a higher stride frequency in downward locomotion. We estimate travel time up or down an old‐growth redwood tree to be on the scale of hours, a significant time investment that may encourage alternatives when available. These results suggest that, in an ecological context, while salamanders are capable of traveling straight down a redwood tree, they may simply tend to jump.

Great ape walking kinematics: Implications for hominoid evolution.

Great apes provide a point of reference for understanding the evolution of locomotion in hominoids and early hominins. We assessed (1) the extent to which great apes use diagonal sequence, diagonal couplet gaits, like other primates, (2) the extent to which gait and posture vary across great apes, and (3) the role of body mass and limb proportions on ape quadrupedal kinematics. High-speed digital video of zoo-housed bonobos (Pan paniscus, N = 8), chimpanzees (Pan troglodytes, N = 13), lowland gorillas (Gorilla gorilla, N = 13), and orangutans (Pongo spp. N = 6) walking over-ground at self-selected speeds were used to determine the timing of limb touch-down, take-off, and to measure joint and segment angles at touch-down, midstance, and take-off. The great apes in our study showed broad kinematic and spatiotemporal similarity in quadrupedal walking. Size-adjusted walking speed was the strongest predictor of gait variables. Body mass had a negligible effect on variation in joint and segment angles, but stride frequency did trend higher among larger apes in analyses including size-adjusted speed. In contrast to most other primates, great apes did not favor diagonal sequence footfall patterns, but exhibited variable gait patterns that frequently shifted between diagonal and lateral sequences. Similarities in the terrestrial walking kinematics of extant great apes likely reflect their similar post-cranial anatomy and proportions. Our results suggest that the walking kinematics of orthograde, suspensory Miocene ape species were likely similar to living great apes, and highlight the utility of videographic and behavioral data in interpreting primate skeletal morphology.

Interlimb coordination during climbing by primates: a test of the Vilensky hypothesis

Primate horizontal locomotion is characterized by a trio of unusual features, including hindlimb‐biased weight support, greater diagonality, and high degrees of forelimb protraction. All of these features are thought to have been influenced by early primates' adoption of a thin‐branch niche. This interpretation has however been challenged based on non‐primate mammals that occupy a similar niche, but do not demonstrate these characteristics. Vilensky (1994) proposed that diagonality evolved in response to greater use of more vertically oriented supports. Nyakatura et al (2008) provided data on tamarins in support of this hypothesis. However, both of these studies examined limited primate species and only on inclined supports, rather than purely vertical supports. Here, we examine diagonality during climbing of vertical supports compared to walking across horizontal supports to the hypothesis first proposed by Vilensky.711 symmetric gait sequences were collected during horizontal walking and vertical climbing by 8 species of primates spanning over an order of magnitude of body weight. Trials were video recorded and footfall sequence were determined for each trial from these recording. From these data, speed, diagonality, interlimb coordination, forelimb and hindlimb duty factor, and handhold patterns were determined and compared between horizontal walking and vertical climbing.During horizontal quadrupedal locomotion, most primates tended to utilize diagonal‐sequence diagonal‐couplet gaits and trots. These gait types involve the contralateral forelimbs and hindlimbs moving together in near‐unison, and therefore limit the portion of the stride that the limbs are arranged as a unilateral bipod. In contrast, during climbing all species demonstrated decreased diagonality (ANCOVA, p<0.0001), thereby increasing the proportion of trots and lateral‐sequence lateral couplet gaits. The degree of this decreased diagonality appears to be species specific, with shorter limbed species demonstrating a greater decrease than longer limbed species. The amount the limbs are in contact with the support also increases during climbing, thereby increasing the number of limbs that are in contact with the support at any one time.Although most primates exhibit primarily diagonal sequence, diagonal couplet gaits during horizontal walking, it appears that climbing does not follow a similar pattern. Diagonality does not increase on vertical supports, as suggested by Vilensky and supported by Nyakatura, although diagonal couplets are retained. Our results are similar to those recently reported by Schoonaert et al (2016) for bonobos. Additionally, duty factor index appears to be increased during climbing. We suggest that these phenomena are due to the propulsive requirements of vertical climbing, which causes hindlimb duty factor to increase disproportionately relative to the forelimb in some primates.Support or Funding InformationThis project was supported by the National Science Foundation, Leakey Foundation, Force and Motion Foundation, National Science Foundation's Graduate Research Fellowship Program, Molly Glander award, Department of Veterinary Sciences at the Michale E. Keeling Center at UT MD Anderson Cancer Center, and Duke University Internal Funding.

Positional behaviour and tail use by the bare-tailed woolly opossum Caluromys philander (Didelphimorphia, Didelphidae)

We present the first quantitative description of postural behaviour of a free ranging metatherian, the bare-tailed woolly opossum, Caluromys philander. Postural behaviour was observed using 10 camera traps set in front of artificial nests, located in the understory of an Atlantic forest site in Rio de Janeiro, Brazil. Seven locomotory and positional modes were identified, with a predominance of diagonal couplets. Individuals used three types of grasp as observed in captivity, but the frequency of digital grasping was higher in the wild. The tail was used as an additional grasping limb, preventing falls and freeing hands to other activities, but the tail was also used to carry leaves for nest building. The use of camera traps may represent a breakthrough in the study of positional behaviours in the wild.

Limb kinematics during locomotion in the two-toed sloth ( Choloepus didactylus, Xenarthra) and its implications for the evolution of the sloth locomotor apparatus

In order to gain insight into the function of the extant sloth locomotion and its evolution, we conducted a detailed videoradiographic analysis of two-toed sloth locomotion (Xenarthra: Choloepus didactylus). Both unrestrained as well as steady-state locomotion was analyzed. Spatio-temporal gait parameters, data on interlimb coordination, and limb kinematics are reported. Two-toed sloths displayed great variability in spatio-temporal gait parameters over the observed range of speeds. They increase speed by decreasing the durations of contact and swing phases, as well as by increasing step length. Gait utilization also varies with no strict gait sequence or interlimb timing evident in slow movements, but a tendency to employ diagonal sequence, diagonal couplet gaits in fast movements. In contrast, limb kinematics were highly conserved with respect to ‘normal’ pronograde locomotion. Limb element and joint angles at touch down and lift off, element and joint excursions, and contribution to body progression of individual elements are similar to those reported for non-cursorial mammals of small to medium size. Hands and feet are specialized to maintain firm connection to supports, and do not contribute to step length or progression. In so doing, the tarsometatarsus lost its role as an individual propulsive element during the evolution of suspensory locomotion. Conservative kinematic behavior of the remaining limb elements does not preclude that muscle recruitment and neuromuscular control for limb pro- and retraction are also conserved. The observed kinematic patterns of two-toed sloths improve our understanding of the convergent evolution of quadrupedal suspensory posture and locomotion in the two extant sloth lineages.

Palmar and Plantar Pressure While Walking on a Horizontal Ladder and Single Pole in Macaca fuscata

To investigate biomechanical function in the hand and foot during quadrupedal locomotion in nonhuman primates, physical anthropologists and primatologists measure the pressure under them. We collected hand and foot pressure data while a Japanese macaque (Macaca fuscata), a semiterrestrial anthropoid, walked on 2 different simulated arboreal substrates, a horizontal ladder and a single pole, to explore differences in hand and foot use between the 2 substrates. The ladder rungs were perpendicular to the craniocaudal axis of the subject, and the pole was parallel to the subject’s craniocaudal axis. We tested the hypothesis that the pole was a more challenging substrate for the macaque than the ladder. Focusing on a diagonal sequence, diagonal couplets gait, we calculated gait characteristics and computed mean peak-pressure images of the hand and foot for each substrate from individual peak images via translation registration. We found several substrate differences that supported the hypothesis. The Japanese macaque walked at significantly slower speeds when traveling on the pole than on the ladder. Slower travel speed on the pole suggests that the Japanese macaque needed a wider support base to maintain balance on this substrate. Mean peak-pressure images suggest that the ladder invoked a more stepping-like behavior, but the pole invoked a more grasping-like behavior, especially of the foot. We show that the hand and foot use of the Japanese macaque would be adaptable to biomechanical challenges posed by different substrates.

Forelimb kinematics of the flat walk and fox trot of the Missouri Fox Trotter

While temporal variable measurements have assisted in objectively defining and distinguishing between four-beat stepping gaits performed by gaited horses, kinematic research describing joint motion of the gaited horse is limited. The objective of this study was to measure the temporal variables and the forelimb kinematics of the flat walk and fox trot of the Missouri Fox Trotter (MFT) to provide a more comprehensive description of these gaits and to assist in distinguishing between them. Reflective markers placed along the lateral aspect of the right forelimb and the zygomatic process of the temporal bone were tracked at 60 Hz as eight MFTs were ridden at a flat walk and fox trot for ten strides. Student's paired t-tests were performed to compare means of analysed parameters between gaits on finding that the fox trot was a faster stepping gait (fox trot velocity: 3.17 ± 0.03 m s− 1, flat walk velocity: 1.75 ± 0.06 m s− 1) with a shorter stride duration (fox trot: 0.63 ± 0.03 s, flat walk: 1.17 ± 0.06 s) and greater stride frequency (fox trot: 1.59 ± 0.09 strides s− 1, flat walk: 0.09 ± 0.04 strides s− 1) than the flat walk (P < 0.05). Both gaits were performed with similar stride length (fox trot: 2.0 ± 0.03 m, flat walk: 1.95 ± 0.05 m), but the fox trot had an irregular rhythm with diagonal couplets (diagonal advanced placement: 0.10 ± 0.01 s, lateral advanced placement: 0.23 ± 0.02 s). Vertical head excursions, protraction/retraction angles and joint angle-time curves for the shoulder, elbow, carpus and forelimb fetlock were similar between gaits. Shoulder peak flexion of the fox trot occurred later in the stride (fox trot: 38 ± 5%, flat walk: 20 ± 3%; P < 0.05), but the timing of the other peak flexion and extension joint angles were similar between gaits. The fox trotting carpus flexed more (fox trot: 136 ± 3°, flat walk: 147 ± 4°) than the carpus of the flat walk (P < 0.05), but the other peak flexion and extension joint angles were comparable between gaits. Measured temporal and kinematic variables assisted in defining the fox trot and flat walk and differences between variables can be applied in distinguishing between the two gaits.

Kinematics of level terrestrial and underwater walking in the California newt, Taricha torosa

Salamanders are acknowledged to be the closest postural model of early tetrapods and are capable of walking both in a terrestrial environment and while submerged under water. Nonetheless, locomotion in this group is poorly understood, as is underwater pedestrian locomotion in general. We, therefore, quantified the movements of the body axis and limbs of the California newt, Taricha torosa, during steady-speed walking in two environments, both of which presented a level surface: a treadmill and a trackway that was submerged in an aquarium. For treadmill walking at a relative speed of 0.63 snout-vent lengths (SVL)/sec, newts used a diagonal couplets lateral sequence walk with a duty factor of 77%. In contrast, submerged speeds were nearly twice as fast, with a mean of 1.19 SVL/sec. The submerged gait pattern was closer to a trot, with a duty factor of only 41%, including periods of suspension. Environment appears to play a critical role in determining gait differences, with reduction of drag being one of the most important determinants in increasing duration of the swing phase. Quantitative analysis of limb kinematics showed that underwater strides were more variable than terrestrial ones, but overall were strikingly similar between the two environments, with joint movement reversals occurring at similar points in the step cycle. It is suggested that the fundamental walking pattern appears to function well under multiple conditions, with only minor changes in motor control necessary.

Gaits of Japanese macaques (Macaca fuscata) on a horizontal ladder and arboreal stability

Most primates use diagonal sequence (DS), diagonal couplets (DC) gaits when they walk or run quadrupedally, and it has been suggested that DSDC gaits contribute to stability in their natural arboreal habitats compared to other symmetrical gaits. However, this postulate is based solely on studies of primate gaits using continuous terrestrial and arboreal substrates. A particular species may select suitable gaits according to the substrate properties. Here, we analyzed the gaits of Japanese macaques moving on a horizontal ladder with rung intervals ranging from 0.40 to 0.80 m to elucidate the relative advantages of each observed form of gait. The rung arrangement forced our macaques to choose either diagonal coupling or DS gaits. One macaque consistently used diagonal coupling (i.e., DSDC and LSDC gaits) across narrow and intermediate rung intervals, whereas the other macaque used DS gaits (i.e., DSDC and DSLC gaits). At wider rung intervals, both macaques shifted to a two-one sequence (TOS), which is characterized by two nearly simultaneous touchdowns of both forelimbs and one touchdown of each hind limb in a stride. The transition to the TOS sequence increased the duration of support on multiple limbs, but always included periods of a whole-body aerial phase. These results suggest that Japanese macaques prefer DSDC gaits, because the diagonal coupling and DS contribute separately to stability on complex supports compared to the lateral coupling and lateral sequence. We also postulate that stability triggers the transition from symmetrical gaits to the TOS sequence.

Description of joint movements in human and non-human primate locomotion using Fourier analysis

To describe and help interpret joint movements in various forms of primate locomotion, we explored the use of Fourier analysis to represent changing joint angles as a series of sine and cosine curves added together to approximate the raw angular data. Results are presented for four joints (shoulder, elbow, hip and knee) with emphasis on the shoulder, and for five types of locomotion (catarhine primate quadrupedal walking, human hands-and-feet creeping and hands-and-knees creeping, and human walking and running). Fourier analysis facilitates functional interpretation of the angles of all four joints, by providing average joint angles and an indication of the number of peaks and troughs in the angular data. The description of limb movements also afforded us the opportunity to compare human and other catarhine joint angles, and we interpret the Fourier results in terms of locomotor posture and type. In addition, the shoulder data are useful for determination of some aspects of interlimb coordination. Non-human primates walking quadrupedally and humans creeping on hands and knees generally evince diagonal couplets interlimb coordination, in which the hand on one side strikes the substrate at about the same time as the contralateral foot or knee. Furthermore, human walking and running seem to follow a similar pattern, as indicated by Fourier analysis. From our data it is concluded that human bipedal gaits are qualitatively similar to diagonal couplets gaits in other primates, but quite different from the lateral couplets gaits used by many non-primate mammals. A number of other benefits of Fourier analysis in primate locomotion studies are also discussed. These include the ability to make statistical comparisons among various types of limb movements in a wide variety of species, a simple archival technique for limb movement data, and a greater understanding of the variability of locomotor movements.

Limb proportions and the ontogeny of quadrupedal walking in infant baboons (Papio cynocephalus)

AbstractMuch of the diversity in preferred walking gait (footfall sequence, interlimb timing) observed among mammals can be understood as a biomechanical response to variation in body shape, in conjunction with efforts to maintain stability. Primates, unlike most other mammals, exhibit a preference for diagonal sequence, diagonal couplets (DSDC) walking gait, but there remains no clear consensus on this gait's possible biomechanical or adaptive advantages. This study examines primate gait from an ontogenetic perspective, and tests the hypothesis that ontogenetic gait transitions are influenced by changes in body shape. Support for this hypothesis could provide insight on the biomechanics and evolution of DSDC gait preferences in adult primates. Data on limb proportions, footfall sequence and interlimb timing were collected at 2‐week intervals for four infant baboons (Papio cynocephalus) as they aged from 1 to 9 months. Despite some variation among individuals, DSDC walking was the most frequently used gait throughout the developmental period, but it was nearly always used in combination with lateral sequence walking. An important transition occurred at c. 5 months, when limb couplets used in lateral sequence walking shifted from diagonal to lateral, and the frequency of DSDC walking increased. The couplets shift within lateral sequence walking coincided with a relative increase in hind limb length, and was most likely attributable to the avoidance of ipsilateral limb interference. Limb proportions thus appear to have a functional influence on lateral sequence walking, but do not explain the consistent use of DSDC walking during the sampled developmental period.

Tuataras and salamanders show that walking and running mechanics are ancient features of tetrapod locomotion.

The lumbering locomotor behaviours of tuataras and salamanders are the best examples of quadrupedal locomotion of early terrestrial vertebrates. We show they use the same walking (out-of-phase) and running (in-phase) patterns of external mechanical energy fluctuations of the centre-of-mass known in fast moving (cursorial) animals. Thus, walking and running centre-of-mass mechanics have been a feature of tetrapods since quadrupedal locomotion emerged over 400 million years ago. When walking, these sprawling animals save external mechanical energy with the same pendular effectiveness observed in cursorial animals. However, unlike cursorial animals (that change footfall patterns and mechanics with speed), tuataras and salamanders use only diagonal couplet gaits and indifferently change from walking to running mechanics with no significant change in total mechanical energy. Thus, the change from walking to running is not related to speed and the advantage of walking versus running is unclear. Furthermore, lumbering mechanics in primitive tetrapods is reflected in having total mechanical energy driven by potential energy (rather than kinetic energy as in cursorial animals) and relative centre-of-mass displacements an order of magnitude greater than cursorial animals. Thus, large vertical displacements associated with lumbering locomotion in primitive tetrapods may preclude their ability to increase speed.

Lateral sequence walking in infant Papio cynocephalus: implications for the evolution of diagonal sequence walking in primates.

One of the most distinctive aspects of primate quadrupedal walking is the use of diagonal sequence footfalls in combination with diagonal-couplets interlimb timing. Numerous hypotheses have been offered to explain why primates might have evolved this type of gait, yet this important question remains unresolved. Because infant primates use a wider variety of quadrupedal gaits than do adults, they provide a natural experiment with which to test hypotheses about the evolution of unique aspects of primate quadrupedalism. In this study, we present kinematic data on two infant baboons (Papio cynocephalus) in order to test the recent hypothesis that diagonal sequence, diagonal couplets walking might have evolved in primates because their limb positioning provides stability in a small branch environment (Cartmill et al. [2002] Zool J Linn Soc 136:401-420). To assess hindlimb position at the moment of forelimb touchdown, we measured hindlimb angular excursion and ankle position for 84 walking strides, across three different types of gaits (diagonal sequence, diagonal couplets (DSDC); lateral sequence lateral couplets (LSLC); and lateral sequence diagonal couplets (LSDC)). Results indicate that if a forelimb were to contact an unstable substrate, LSLC walking provides as much, and perhaps more, stability when compared to DSDC walking. Therefore, it appears that this moment in a stride was unlikely to be a particularly important selective factor in the evolution of DSDC walking. Further insight into this issue will likely be gained by observations of primate quadrupedalism in natural environments, where the use of lateral sequence gaits might be more common than currently known.

Temporal variables of four-beat, stepping gaits of gaited horses

Gaited horse breeds perform a variety of four-beat stepping gaits that are recognized and distinguished by the sequence and timing of the footfalls and by the limb support sequences during the stride. The popularity of the gaited horse breeds is increasing and accurate descriptions of limb kinematics are needed both to define the performance characteristics of the different gaits and to assist in identifying gait pathologies. The objective of this study was to measure the temporal stride variables of 16 four-beat stepping gaits using frame-by-frame analysis. The gait sequences used for analysis were selected by the breed associations as being representative of correct performance of each gait. The results showed that all gaits were classified as symmetrical. A regular four-beat rhythm was present in the classic fino, coon rack, marcha picada, mountain pleasure rack, paso llano, rocky mountain rack, style rack, road gait, and toelt. An irregular rhythm with diagonal couplets characterized the fox trot, marcha batida, paso corto, and paso largo, while lateral couplets were found in the running walk, curly rack, and sobreandando. Three distinct limb support sequences were identified, with only the marcha batida demonstrating a period of quadrupedal support. Hind limb stance was longer than forelimb stance in the paso corto, paso largo, style rack, and running walk.

Overground locomotion in intact rats: interlimb coordination, support patterns and support phases duration

The interlimb coordination during overground locomotion was analysed in intact rats, using the method of contact electrodes (Górska et al. 1998). It was found that in animals moving with a speed ranging from 10 to 78 cm/s (step cycles 685 to 215 ms, respectively) the interlimb coordination was characterized by homologous phase shifts close to 0.5 and much shorter diagonal than lateral phase shifts. These features corresponded to symmetrical gait with diagonal sequence and diagonal couplets (Hildebrandt 1976). Shortening the step cycle changed the gait from a walking trot (duty factor &gt;0.5) into a running trot (duty factor

Ground reaction forces in locomoting hemi-parkinsonian rats: a definitive test for impairments and compensations.

Hemi-parkinsonian rats have preserved postural reflexes but are impaired in initiation of voluntary movements. Surprisingly, these rats can walk and run, suggesting that they can access some compensatory strategy to overcome the rigidity in their impaired limbs. The purpose of the present experiment was to investigate the locomotor compensations made by hemi-parkinsonian rats by measuring the forces exerted by the limbs on the ground throughout the stride during trotting. Rats with unilateral dopamine depletion produced by injection of 6-hydroxydopamine into the nigrostriatal bundle were trained to run back and forth in an alley for food reinforcement. Ground reaction forces were measured in three orthogonal directions using a force plate embedded in the runway. Rats were also videotaped so that limb movements were synchronized with force recordings. Although locomotion was obviously impaired, the affected limbs could support weight and provide some braking forces. In addition, the impaired hindlimb provided significant propulsive force, and a relatively large laterally directed force. Analysis of vertical movement of the centre of mass suggested that the impaired hindlimb was being used partly as a spring. The most significant abnormalities were seen during the diagonal couplet of the impaired forelimb and the unimpaired hindlimb, partly reflecting the important compensatory role of the unimpaired hindlimb. These results demonstrate that this method is useful in the analysis of hemi-parkinsonian gait and provide insights as to how rats can use an impaired limb to produce weight support and propulsion.

Footfall patterns in the early development of the quadrupedal walking of Japanese macaques.

The development of quadrupedal walking in infant Japanese macaques (Macaca fuscata) was studied on the basis of their footfall patterns. Lateral views of the walking of 5 monkeys were taken by a video-camera and the timing of touchdown and liftoff was recorded. The total number of trials was 435. The change of footfall patterns during development was complicated. Four stages could be discerned, as in behavioural studies. In the first stage, there was a wide variation. The dominant patterns were the diagonal sequence which included any type of couplet in the second stage and trot in the third stage. There were two groups of footfall patterns in the fourth stage which were the diagonal sequence-diagonal couplet and the lateral sequence-lateral couplet. It seems that the stages reflect aspects of the development of both the neural system and the musculoskeletal system.

Temporal characteristics of the fox trot, a symmetrical equine gait

The temporal characteristics of the equine gait known as the fox trot are described. Data were obtained from cine films of three horses ( Equus caballus), with five strides being analysed for each horse. The results show that the fox trot has a lateral sequence of limb placements: left hind, left front, right hind, right front. The rhythm of the footfalls is characterised by diagonal couplets with impact of the forelimb being followed by the diagonal hind limb after an interval of 15% of the stride duration, whereas impact of the forelimb follows that lateral hind limb by 35% of the stride duration. The mean stride duration was 593.3 ms which is equivalent to a stride frequency of 101 strides min −1. The stance durations of the forelimbs and hind limbs were 54% of the stride duration, indicating that the fox trot is a walking gait without any periods of suspension. During a complete stride the body was supported by eight distinct limb combinations. For each half of the stride the limb support sequence expressed as a percentage of the stride duration was tripedal with two hind limbs and one forelimb (8.9%), diagonal bipedal (60.6%), tripedal with one hind limb and two forelimbs (8.9%), and lateral bipedal (21.7%).

Why cats pace on the treadmill

There have been many studies suggesting that locomotion on a treadmill tends to be different than locomotion at similar velocities overground, but no satisfactory mechanical or neural mechanisms to account for the differences have been identified. The most prominent difference is the tendency to adopt a pacing gait for both walking and trotting speeds, in which the legs on one side of the body move in phase as lateral couplets rather than the typical diagonal couplet pattern seen overground. Using conventional video analysis, we quantified the gait patterns of intact, adult cats walking at various speeds overground and in a motorized treadmill. We noted that cats paced most frequently when they were at the front end of the treadmill enclosure, and that this gait was associated with an extended stride length that permitted the animals to maintain a higher duty factor of support (mean number of feet on the ground). We propose that the animal extends its stride specifically to improve the duty factor in anticipation of sudden stops of the treadmill belt and that it converts abruptly from diagonal to lateral gait because the extended stride results in collisions between ipsilateral hind and front feet.