[Comparative Biomechanics of Canine Agility].

Agility is a sport in which dogs compete on an obstacle course for both accuracy and time. Dogs that participate in competitions must negotiate a complex course of approximately 20 obstacles. We describe a literature review of the biomechanics of canine agility and our preliminary results. The number of articles that have reported biomechanics of canine agility has gradually increased since 2010. Most previous studies have focused on the bar jump, which is a basic obstacle to agility. In our preliminary study, we investigated the roll motion of the head and trunk using inertial sensors for Border Collies that completed weave poles (obstacles in which dogs weave through approximately 10 poles placed 0.6 m apart in a straight line). The roll angles of the head and trunk were measured based on the angular velocity and linear acceleration data using a sensor fusion algorithm. The head and trunk rotated about the roll axis nearly in unison. The roll amplitude of the head was lower than that of the trunk. We discuss the importance of biomechanical studies on canine agility to gain a deeper understanding of mammalian quadrupedal locomotion.

[Posture Control Associated with Quadrupedal and Bipedal Gait in Japanese Monkeys (Macaca fuscata)].

How the CNS deals with instability of upright posture is the core in the control of bipedal gait. In this review, we summarize our recent findings comparing kinematics and EMG activity during quadrupedal and bipedal gait in Japanese macaques. Trunk/hindlimb muscles showed step cycle-modulated activity, which was more active in bipedal than in quadrupedal gait. For bipedal gait, enhanced activity during longer double support phase was predominantly observed in distal hindlimb muscles. Alternate burst activity in bilateral back muscles cyclically brought back the tilted trunk. In monkeys' quadrupedal gait, hindlimbs formed functional pairs with contralateral forelimbs, unlike in non-primate quadrupeds. These diagonal pairs acted differently on movements of the center of mass (COM). For bipedal gait, the hindlimbs solely carried the COM. Our results suggest that, compared to non-primate quadrupeds, hindlimbs in macaques contribute more critically to weight support and balance control even for quadrupedal gait. Additionally, for more unstable bipedal gait, the monkeys' CNS reinforces such hindlimb roles and actively controls the trunk posture in maintaining dynamic balance, in a manner similar to humans. Studies on Japanese macaques will further our understanding of the neural basis for the control of gait in mammals by bridging non-primate quadrupeds and humans.

Three Characteristics of Cheetah Galloping Improve Running Performance Through Spinal Movement: A Modeling Study.

Cheetahs are the fastest land animal. Their galloping shows three characteristics: small vertical movement of their center of mass, small whole-body pitching movement, and large spine bending movement. We hypothesize that these characteristics lead to enhanced gait performance in cheetahs, including higher gait speed. In this study, we used a simple model with a spine joint and torsional spring, which emulate the body flexibility, to verify our hypothesis from a dynamic perspective. Specifically, we numerically searched periodic solutions and evaluated what extent each solution shows the three characteristics. We then evaluated the gait performance and found that the solutions with the characteristics achieve high performances. This result supports our hypothesis. Furthermore, we revealed the mechanism for the high performances through the dynamics of the spine movement. These findings extend the current understanding of the dynamic mechanisms underlying high-speed locomotion in cheetahs.

Center of Mass Offset Enhances the Selection of Transverse Gallop in High-Speed Running by Horses: A Modeling Study.

Horses use the transverse gallop in high-speed running. However, different animals use different gaits, and the gait preference of horses remains largely unclear. Horses have fore-aft asymmetry in their body structure and their center of mass (CoM) is anteriorly located far from the center of the body. Since such a CoM offset affects the running dynamics, we hypothesize that the CoM offset of horses is important in gait selection. In order to verify our hypothesis and clarify the gait selection mechanisms by horses from a dynamic viewpoint, we developed a simple model with CoM offset and investigated its effects on running. Specifically, we numerically obtained periodic solutions and classified these solutions into six types of gaits, including the transverse gallop, based on the footfall pattern. Our results show that the transverse gallop is optimal when the CoM offset is located at the position estimated in horses. Our findings provide useful insight into the gait selection mechanisms in high-speed running of horses.

Kinematic adjustments to arboreal locomotion in Japanese macaques (Macaca fuscata).

Although biomechanical adaptations to arboreal locomotion have been well investigated in primates and other mammals in laboratory settings, the results are not consistent, and more species need to be studied to build a comprehensive picture of this. Here, we used three-dimensional videography to quantify kinematic parameters thought to be associated with locomotor stability while two Japanese macaques walked on terrestrial and simulated arboreal substrates (a horizontal pole, which was narrow relative to the animal's body width). The parameters investigated included temporal-spatial gait variables, those associated with compliant walking, the height of the shoulder and hip, and hand and foot clearance during the swing phase. We found that there were many individual differences in kinematic adjustments made by the monkeys during arboreal locomotion. More importantly, the results were consistent between the monkeys for three parameters: maximum hand clearance, maximum hip height, and maximum foot clearance. The monkeys showed lower maximum hand and foot clearances during arboreal locomotion than during terrestrial locomotion, indicating that the hands and feet were kept close to the substrate surface during the swing phase. They also showed lower maximum hip heights during arboreal locomotion, suggesting that their whole-body centers of mass were lowered. These consistent kinematic adjustments can be interpreted as strategies for enhancing stability and reducing the risk of falling from a height. Overall, these results show that Japanese macaques make significant biomechanical adaptations to arboreal locomotion that are not fully consistent with existing data for other animals.

Dynamical determinants enabling two different types of flight in cheetah gallop to enhance speed through spine movement.

Cheetahs use a galloping gait in their fastest speed range. It has been reported that cheetahs achieve high-speed galloping by performing two types of flight through spine movement (gathered and extended). However, the dynamic factors that enable cheetahs to incorporate two types of flight while galloping remain unclear. To elucidate this issue from a dynamical viewpoint, we developed a simple analytical model. We derived possible periodic solutions with two different flight types (like cheetah galloping), and others with only one flight type (unlike cheetah galloping). The periodic solutions provided two criteria to determine the flight type, related to the position and magnitude of ground reaction forces entering the body. The periodic solutions and criteria were verified using measured cheetah data, and provided a dynamical mechanism by which galloping with two flight types enhances speed. These findings extend current understanding of the dynamical mechanisms underlying high-speed locomotion in cheetahs.

Underground locomotion in moles: kinematic and electromyographic studies of locomotion in the Japanese mole (Mogera wogura).

A series of kinematic and electromyographic (EMG) studies were conducted to characterize the neural control of underground movement in the Japanese mole, Mogera wogura. For the purposes of the present study, the locomotion of moles was classified into two modes: crawling, which comprises alternate movements of the left and right forelimbs; and burrowing, in which both forelimbs move synchronously. In crawling, moles exhibit both symmetrical and asymmetrical locomotion independent of cycle duration and speed of travel. In burrowing, the movements of fore- and hindlimbs, and of the left and right hindlimb are loosely coordinated. We divided cycles of limb movement into recovery stroke phase and power stroke phases and observed that control of cycle duration in forelimbs and hindlimbs was achieved through changes to both recovery and power stroke phases. Our results showed phasic EMG bursts in various muscles in moles, whose timing differed from that seen in terrestrial four-legged mammals such as cats and dogs. The difference was especially apparent in the m. longissimus, in which EMG bursts recorded at the level of the thoracic and lumbar vertebrae corresponded to movements of the forelimbs and hindlimbs, respectively. Thus, we conclude that moles have evolved a distinctive mechanism of neural control to perform their specialized forms of underground locomotion.

Locomotor kinematics and EMG activity during quadrupedal versus bipedal gait in the Japanese macaque.

Several qualitative features distinguish bipedal from quadrupedal locomotion in mammals. In this study we show quantitative differences between quadrupedal and bipedal gait in the Japanese monkey in terms of gait patterns, trunk/hindlimb kinematics, and electromyographic (EMG) activity, obtained from 3 macaques during treadmill walking. We predicted that as a consequence of an almost upright body axis, bipedal gait would show properties consistent with temporal and spatial optimization countering higher trunk/hindlimb loads and a less stable center of mass (CoM). A comparatively larger step width, an ~9% longer duty cycle, and ~20% increased relative duration of the double-support phase were all in line with such a strategy. Bipedal joint kinematics showed the strongest differences in proximal, and least in distal, hindlimb joint excursions compared with quadrupedal gait. Hindlimb joint coordination (cyclograms) revealed more periods of single-joint rotations during bipedal gait and predominance of proximal joints during single support. The CoM described a symmetrical, quasi-sinusoidal left/right path during bipedal gait, with an alternating shift toward the weight-supporting limb during stance. Trunk/hindlimb EMG activity was nonuniformally increased during bipedal gait, most prominently in proximal antigravity muscles during stance (up to 10-fold). Non-antigravity hindlimb EMG showed altered temporal profiles during liftoff or touchdown. Muscle coactivation was more, but muscle synergies less, frequent during bipedal gait. Together, these results show that behavioral and EMG properties of bipedal vs. quadrupedal gait are quantitatively distinct and suggest that the neural control of bipedal primate locomotion underwent specific adaptations to generate these particular behavioral features to counteract increased load and instability. NEW & NOTEWORTHY Bipedal locomotion imposes particular biomechanical constraints on motor control. In a within-species comparative study, we investigated joint kinematics and electromyographic characteristics of bipedal vs. quadrupedal treadmill locomotion in Japanese macaques. Because these features represent (to a large extent) emergent properties of the underlying neural control, they provide a comparative, behavioral, and neurophysiological framework for understanding the neural system dedicated to bipedal locomotion in this nonhuman primate, which constitutes a critical animal model for human bipedalism.

Anatomical variation of habitat-related changes in scapular morphology.

The mammalian forelimb is adapted to different functions including postural, locomotor, feeding, exploratory, grooming and defence. Comparative studies on morphology of the mammalian scapula have been performed in an attempt to establish the functional differences in the use of the forelimb. In this study, a total of 102 scapulae collected from 66 species of animals, representatives of all major taxa from rodents, sirenians, marsupials, pilosa, cetaceans, carnivores, ungulates, primates and apes, were analysed. Parameters measured included scapular length, width, position, thickness, area, angles and index. Structures included supraspinous and infraspinous fossae, scapular spine, glenoid cavity, acromium and coracoid processes. Images were taken using computed tomographic (CT) scanning technology (CT-Aquarium, Toshiba and micro CT-LaTheta, Hotachi, Japan), and measurement values were acquired and processed using Avizo computer software and CanvasTM 11 ACD systems. Statistical analysis was performed using Microsoft Excel 2013. Results obtained showed that there were differences in morphological characteristics of scapula between mammals with arboreal locomotion and living in forest and mountainous areas and those with leaping and terrestrial locomotion living in open habitat or savannah. Differences were seen in the ratio of maximum length and maximum width, the orientation of scapular spine and the horizontal length of acromion and coracoid processes. The cause for the statistical grouping of the animals and the way the scapular shape covaries with habitat and to the type of locomotion and speed are discussed in detail.

Characteristics of Muscle Fiber-Type Distribution in Moles.

Moles are a strictly fossorial Soricomorpha species and possess a suite of specialized adaptations to subterranean life. However, the contractile function of skeletal muscles in moles remains unclear. We compared muscle fiber-type distribution in two mole species (the large Japanese mole and lesser Japanese mole) with that in four other Soricomorpha species that are semi-fossorial, terrestrial, or semi-aquatic (the Japanese shrew-mole, house shrew, Japanese white-toothed shrew, and Japanese water shrew). For a single species, the fiber-type distribution in up to 38 muscles was assessed using immunohistochemical staining and/or gel electrophoresis. We found that slow and fatigue-resistant Type I fibers were absent in almost all muscles of all species studied. Although, the two methods of determining the fiber type did not give identical results, they both revealed that fast Type IIb fibers were absent in mole muscles. The fiber-type distribution was similar among different anatomical regions in the moles. This study demonstrated that the skeletal muscles of moles have a homogenous fiber-type distribution compared with that in Soricomorpha species that are not strictly fossorial. Mole muscles are composed of Type IIa fibers alone or a combination of Type IIa and relatively fast Type IIx fibers. The homogenous fiber-type distribution in mole muscles may be an adaptation to structurally simple subterranean environments, where there is no need to support body weight with the limbs, or to move at high speeds to pursue prey or to escape from predators. Anat Rec, 302:1010-1023, 2019. © 2018 Wiley Periodicals, Inc.

Intra-individual variation in hand postures during terrestrial locomotion in Japanese macaques (Macaca fuscata).

The primate hand adopts a variety of postures during locomotion. Habitually terrestrial cercopithecine primates are known to use a palmigrade posture at faster speeds to possibly mitigate stresses on the hand skeleton; however, it is unclear whether arboreal or semi-terrestrial species use a similar strategy for adjusting hand posture. Here, we explored intra-individual variation in hand contact patterns during terrestrial locomotion in the Japanese macaque (Macaca fuscata), a semi-terrestrial cercopithecine primate. Two monkeys were required to walk on the ground at their own preferred speeds or were encouraged to move faster for food rewards. The contact area under the hand and ground reaction forces (GRFs) were measured simultaneously using a tactile pressure sensor, and then hand pressures were calculated offline. We found that hand contact patterns could vary within individuals. The monkeys used predominantly a palmigrade posture within the range of speeds covered in this study (0.72-2.56 m s-1). There were two subtypes of palmigrade posture. In one subtype, the hypothenar pad did not contact the substrate, whereas the entire hand contacted the substrate in the other. The palm of the palmigrade hand with total-hand contact experienced similar or lower peak pressure and pressure-time integral than those of the palmigrade hand without hypothenar pad contact even though it experienced higher peak GRFs. The moderate peak pressure experienced by the palmigrade hand with total-hand contact was due to increased contact area under the palm. The total contact area of the fingers and peak GRF to the fingers were relatively unchanged with different patterns of hand contact. These findings provide evidence that when walking on the ground, semi-terrestrial Japanese macaques use a palmigrade posture with total-hand contact to attenuate stresses on hand bones, as do habitually terrestrial species.

Brief communication: Dynamic plantar pressure distribution during locomotion in Japanese macaques (Macaca fuscata).

To better place the form and motion of the human foot in an evolutionary context, understanding how foot motions change when quadrupeds walk bipedally can be informative. For this purpose, we compared the pressures beneath the foot during bipedal and quadrupedal walking in Japanese macaques (Macaca fuscata). The pressure at nine plantar regions was recorded using a pressure mat (120 Hz), while the animals walked on a level walkway at their preferred speeds. The results revealed substantial differences in foot use between the two modes of locomotion, and some features observed during bipedal walking resembled human gait, such as the medial transfer of the center of pressure (COP), abrupt declines in forefoot pressures, and the increased pressure beneath the hallux, all occurring during the late-stance phase. In particular, the medial transfer of the COP, which is also observed in bonobos (Vereecke et al.: Am J Phys Anthropol 120 (2003) 373-383), was due to a biomechanical requirement for a hind limb dominant gait, such as bipedal walking. Features shared by bipedal and quadrupedal locomotion that were quite different from human locomotion were also observed: the heel never contacted the ground, a foot longitudinal arch was absent, the hallux was widely abducted, and the functional axis was on the third digit, not the second.

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.

Density of muscle spindles in prosimian shoulder muscles reflects locomotor adaptation.

We examined the correlation between the density of muscle spindles in shoulder muscles and the locomotor mode in three species of prosimian primates: the slow loris (Nycticebus coucang), Garnett's galago (Otolemur garnettii), and the ring-tailed lemur (Lemur catta). The shoulder muscles (supraspinatus, infraspinatus, teres major, teres minor, and subscapularis) were embedded in celloidin and cut into transverse serial thin sections (40 microm); then, every tenth section was stained using the Azan staining technique. The relative muscle weights and the density of the muscle spindles were determined. The slow loris muscles were heavier and had sparser muscle spindles, as compared to Garnett's galago. These features suggest that the shoulder muscles of the slow loris are more adapted to generating propulsive force and stabilizing the shoulder joint during locomotion and play a less controlling role in forelimb movements. In contrast, Garnett's galago possessed smaller shoulder muscles with denser spindles that are suitable for the control of more rapid locomotor movements. The mean relative weight and the mean spindle density in the shoulder muscles of the ring-tailed lemur were between those of the other primates, suggesting that the spindle density is not simply a consequence of taxonomic status.