Hiroo Kumakura

3D Analysis of Human Locomotion Before and After Caloric Stimulation

Human locomotion was analysed in the sagittal and coronal planes using a position detector system composed of 2 infrared video cameras and a data processor. Normal healthy volunteers with 8 marker points on the body were asked to walk in place (WIP) and on a treadmill (WOT). Vertical and medial/lateral (M/L) translational movements were measured. Head angular movements in the sagittal (pitch) and coronal (roll) planes were also analysed. Pitch movements counteracted the vertical head movements. Head movement was remarkably attenuated in the vertical axis compared with that of the trunk. However, head M/L movement showed no difference with that of the lower part of the body. Ice water caloric stimulation was introduced to cause acute unilateral vestibular deficit. The stride length and step cycle became small after caloric stimulation in WOT, but not in WIP. The characteristic change in locomotive pattern was a large lateral sway of the hip joint occurring to the side away from calorization (right) during one foot standing (right foot) (t-test, p = 0.057). Measurement of M/L sway amplitude showed an increase only at the hip joint. As the changes in head and neck movements were not significant after caloric stimulation, it appears that the vestibulo-spinal reflex contributes little to maintaining the dynamic balance of the upper body. The importance of the hip joint for locomotion (hip strategy) was confirmed from the present data.

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.

Head movements during locomotion in a gibbon and Japanese macaques

Kinematic analysis of head and body movements during locomotion in Macaca fuscata and Hylobates lar revealed that coordinated head rotation and translation that have been reported to play an important role in stabilizing gaze during locomotion for humans are also observed in non-human primates. The fact that well-coordinated head movements were observed in two species, and during both bipedal and quadrupedal walking, suggests that the head orientation during locomotion is well regulated in the manner of top-down control over the species and modes of locomotion. The result validates the monkey model and enables us to explore the underlying mechanisms for gaze, head, and postural control during locomotion.

Organization of the Epaxial Muscles in Terrestrial and Arboreal Primates

The erector spinae muscles of the patas monkey hamadryas baboon, and spider monkey were dissected and the origins and insertions were described in detail. In the two terrestrial monkeys, a well-developed thoracolumbar segment of the muscle was observed. This trait seems to correlate to the sagittal movement of this region required in the pronograde quadrupedal locomotion. On the other hand, the erector spinae muscle of the spider monkey is quantitatively not so well developed and the arrangement of the muscle bundles was simpler than in the terrestrial monkeys. The arboreal habit of the spider monkey seems not to demand powerful extension in the thoracolumbar junction, and spinal rotation seems to be more important.

Patterns of Vertical Climbing in Primates

In primates, most adaptive radiations were initiated in arboreal habitats, and subsequent colonization of variable habitats necessitated the development of a notable range of morphological characteristics and locomotor repertoires. Each species of living primates has a specific locomotor pattern that is appropriate to their lifestyle. Human bipedalism is the result of one of the radiations; however, the evolutionary process is difficult to trace, which is also the case for other primate species. Experimental and field studies on vertical climbing may provide clues to the process. It is one of the most important locomotor skills for many taxa of primates, and it occurs in numerous species that are categorized into several locomotor types (Cant, 1988; Doran, 1992; Fleagle, 1976; Gebo, 1992; Mittermeier and Fleagle, 1976). Researchers have examined muscle activities or kinematics during vertical climbing (Hirasaki et al., 1995; Jungers et al., 1983; Larson et al., 1986; Stern et al., 1976; Stern et al., 1981; Vangor et al., 1983; Isler, 2005). Primate species have various strategies for climbing vertically. Each species has a specific mode of vertical climbing adapted to their morphology and lifestyle. We analyzed vertical climbing in 5 species of primates via kinematic experiments in order to clarify the specific characteristics of vertical climbing among primates. This provides clues for unveiling the locomotor modes of fossil primates.

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.

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 µm); 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.

The estimated mechanical advantage of the prosimian ankle joint musculature, and implications for locomotor adaptation

In this study we compared the power arm lengths and mechanical advantages attributed to 12 lower leg muscles across three prosimian species. The origins and insertions of the lower leg muscles in Garnetts galago, the ring‐tailed lemur, and the slow loris were quantified and correlated with positional behaviour. The ankle joint of the galago has a speed‐oriented mechanical system, in contrast to that of the slow loris, which exhibits more power‐oriented mechanics. The lemur ankle joint exhibited intermediate power arm lengths and an intermediate mechanical advantage relative to the other primates. This result suggests that the mechanical differences in the ankle between the galago and the lemur, taxa that exhibit similar locomotory repertoires, reflect a difference in the kinematics and kinetics of leaping (i.e. generalised vs. specialised leapers). In contrast to leaping primates, lorises have developed a more power‐oriented mechanical system as a foot adaptation for positional behaviours such as bridging or cantilevering in their arboreal habitat.

Estimating the Functional Axis of the Primate Foot Using the Distribution of Plantar Muscles

Morton (American Journal of Physical Anthropology 5, 305–336, 1922) used the longest metatarsal, which he assumed functions as a lever during locomotion, to define the functional axis of the primate foot. In humans and apes, the functional foot axis lies on the second digit, whereas that of nonhominoid anthropoids is mostly on the third digit, suggesting that a medial shift of the functional axis occurred during primate foot evolution. Myological observations support this idea; the dorsal interossei of the human foot are arranged around the second digit, whereas those of nonhominoid anthropoids are around the third digit. However, it is still unclear when, why, and how such a change in foot musculature occurred. In addition, there is inconsistency among the limited number of studies that have examined foot musculature in apes. We examined modifications in the interosseous muscles of the chimpanzee, gibbon, spider monkey, and Japanese macaque in terms of the shift in the functional foot axis. We found that the dorsal interossei are arranged around the third digit; this is true even in the chimpanzee, whose functional axis based on metatarsal length lies on the second digit. This suggests that the change in the arrangement of the interosseous muscles phylogenetically lagged behind the shift of the osteological axis. Our results also indicate that the dorsal interossei are composite muscles consisting of the deep short flexors and the intermetatarsal abductors. We postulate that changes in the contributions of these 2 components to the formation of dorsal interossei likely occurred in the hominin lineage, resulting in the medial shift of the myological axis. The medial shift of the functional foot axis may have started with the elongation of the second metatarsal in the hominoid ancestors’ lineage, and was completed on the rearrangement of the interosseous muscles.