The effects of substratum inclination on locomotor patterns in primates

To explore the change from the horizontal quadrupedal walking to the vertical climbing in primates, I designed an experiment on an inclined substratum. The subjects were an adult male Japanese macaque and a 2-year-old female white-handed gibbon. The animals moved on a substratum made of bamboo pipe (8 cm diameter). The inclination of the substratum was changed from 15 degrees to 65 degrees in 5-degree increments for the Japanese macaque and from 20 degrees to 70 degrees with 10-degree increments for the white-handed gibbon. I placed surface electrodes and telemetry transmitters on the subjects to record the activity of the long head of the triceps brachii and the long head of the biceps brachii muscles. The Japanese macaque utilized horizontal quadrupedal walking until the incline was 15 degrees. Vertical climbing began at an inclination of 55 degrees. The intermediate locomotor mode was observed between 20 degrees and 50 degrees. The white-handed gibbon changed the locomotor mode from horizontal quadrupedal walking to vertical climbing at 40 degrees. I believe that the difference observed in locomotor mode between these two species was mainly due to differences in the intermembral index. The white-handed gibbon had a large intermembral index, which meant she had longer forelimbs and could therefore change locomotor mode at a lower inclination of the substratum.     

EMG-angle relationship of the hamstring muscles during maximum knee flexion.

The aim of the present study was to investigate the EMG-joint angle relationship during voluntary contraction with maximum effort and the differences in activity among three hamstring muscles during knee flexion. Ten healthy subjects performed maximum voluntary isometric and isokinetic knee flexion. The isometric tests were performed for 5 s at knee angles of 60 and 90 degrees. The isokinetic test, which consisted of knee flexion from 0 to 120 degrees in the prone position, was performed at an angular velocity of 30 degrees /s (0.523 rad/s). The knee flexion torque was measured using a KIN-COM isokinetic dynamometer. The individual EMG activity of the hamstrings, i.e. the semitendinosus, semimembranosus, long head of the biceps femoris and short head of the biceps femoris muscles, was detected using a bipolar fine wire electrode. With isometric testing, the knee flexion torque at 60 degrees knee flexion was greater than that at 90 degrees. The mean peak isokinetic torque occurred from 15 to 30 degrees knee flexion angle and then the torque decreased as the knee angle increased (p<0.01). The EMG activity of the hamstring muscles varied with the change in knee flexion angle except for the short head of the biceps femoris muscle under isometric condition. With isometric contraction, the integrated EMGs of the semitendinosus and semimembranosus muscles at a knee flexion angle of 60 degrees were significantly lower than that at 90 degrees. During maximum isokinetic contraction, the integrated EMGs of the semitendinosus, semimembranosus and short head of the biceps femoris muscles increased significantly as the knee angle increased from 0 to 105 degrees of knee flexion (p<0.05). On the other hand, the integrated EMG of the long head of the biceps femoris muscle at a knee angle of 60 degrees was significantly greater than that at 90 degrees knee flexion with isometric testing (p<0.01). During maximum isokinetic contraction, the integrated EMG was the greatest at a knee angle between 15 and 30 degrees, and then significantly decreased as the knee angle increased from 30 to 120 degrees (p<0.01). These results demonstrate that the EMG activity of hamstring muscles during maximum isometric and isokinetic knee flexion varies with change in muscle length or joint angle, and that the activity of the long head of the biceps femoris muscle differs considerably from the other three heads of hamstrings.     

Biomechanical analysis of vertical climbing in the spider monkey and the Japanese macaque

Climbing is one of the most important components of primate locomotor modes. We previously reported that the kinesiological characteristics of vertical climbing by the spider monkey and Japanese macaque are clearly different, based on their kinetics and kinematics. In this study, a more detailed analysis using inverse dynamics was conducted to estimate the biomechanical characteristics of vertical climbing in the spider monkey and Japanese macaque. One of the main findings was the difference in forelimb use by the two species. The results of a joint moment analysis and estimates of muscular force indicate that the spider monkey uses its forelimbs to keep the body close to the substrate, rather than to generate propulsion. The forelimb of the Japanese macaque, on the other hand, likely contributes more to propulsion. This supports the idea that "forelimb-hindlimb differentiation" is promoted in the spider monkey. The estimated muscular force also suggests that the spider monkey type of climbing could develop the hindlimb extensor muscles, which are important in bipedal posture and walking. As a result, we conclude that the spider monkey type of climbing could be functionally preadaptive for human bipedalism. This type of climbing would develop the hip and knee extensor muscles, and result in more extended lower limb joints, a more erect trunk posture, and more functionally differentiated fore- and hindlimbs, all of which are important characteristics of human bipedalism.     

Forward dynamic simulation of bipedal walking in the Japanese macaque: investigation of causal relationships among limb kinematics, speed, and energetics of bipedal locomotion in a nonhuman primate

Japanese macaques that have been trained for monkey performances exhibit a remarkable ability to walk bipedally. In this study, we dynamically reconstructed bipedal walking of the Japanese macaque to investigate causal relationships among limb kinematics, speed, and energetics, with a view to understanding the mechanisms underlying the evolution of human bipedalism. We constructed a two-dimensional macaque musculoskeletal model consisting of nine rigid links and eight principal muscles. To generate locomotion, we used a trajectory-tracking control law, the reference trajectories of which were obtained experimentally. Using this framework, we evaluated the effects of changes in cycle duration and gait kinematics on locomotor efficiency. The energetic cost of locomotion was estimated based on the calculation of mechanical energy generated by muscles. Our results demonstrated that the mass-specific metabolic cost of transport decreased as speed increased in bipedal walking of the Japanese macaque. Furthermore, the cost of transport in bipedal walking was reduced when vertical displacement of the hip joint was virtually modified in the simulation to be more humanlike. Human vertical fluctuations in the body's center of mass actually contributed to energy savings via an inverted pendulum mechanism.     

Energetic costs of bipedal and quadrupedal walking in Japanese macaques

We investigated the energetic costs of quadrupedal and bipedal walking in two Japanese macaques. The subjects were engaged in traditional bipedal performance for years, and are extremely adept bipeds. The experiment was conducted in an airtight chamber with a gas analyzer. The subjects walked quadrupedally and bipedally at fixed velocities (<5 km/hr) on a treadmill in the chamber for 2.5-6 min. We estimated energy consumption from carbon dioxide (CO2) production. While walking bipedally, energetic expenditure increased by 30% relative to quadrupedalism in one subject, and by 20% in another younger subject. Energetic costs increased linearly with velocity in quadrupedalism and bipedalism, with bipedal/quadrupedal ratios remaining almost constant. Our experiments were relatively short in duration, and thus the observed locomotor costs may include presteady-state high values. However, there was no difference in experimental duration between bipedal and quadrupedal trials. Thus, the issue of steady state cannot cancel the difference in energetic costs. Furthermore, we observed that switching of locomotor mode (quadrupedalism to bipedalism) during a session resulted in a significant increase of CO2 production. Taylor and Rowntree ([1973] Science 179:186-187) noted that the energetic costs for bipedal and quadrupedal walking were the same in chimpanzees and capuchin monkeys. Although the reason for this inconsistency is not clear, species-specific differences should be considered regarding bipedal locomotor energetics among nonhuman primates. Extra costs for bipedalism may not be great in these macaques. Indeed, it is known that suspensory locomotion in Ateles consumes 1.3-1.4 times as much energy relative to quadrupedal progression. This excess ratio surpasses the bipedal/quadrupedal energetic ratios in these macaques.     

Length and moment arm of human leg muscles as a function of knee and hip-joint angles

Lengths of muscle tendon complexes of the quadriceps femoris muscle and some of its heads, biceps femoris and gastrocnemius muscles, were measured for six limbs of human cadavers as a function of knee and hip-joint angles. Length-angle curves were fitted using second degree polynomials. Using these polynomials the relationships between knee and hip-joint angles and moment arms were calculated. The effect of changing the hip angle on the biceps femoris muscle length is much larger than that of changing the knee angle. For the rectus femoris muscle the reverse was found. The moment arm of the biceps femoris muscle was found to remain constant throughout the whole range of knee flexion as was the case for the medial part of the vastus medialis muscle. Changes in the length of the lateral part of the vastus medialis muscle as well as the medial part of the vastus lateralis muscle are very similar to those of vastus intermedius muscle to which they are adjacent, while those changes in the length of the medial part of the vastus medialis muscle and the lateral part of the vastus lateralis muscle, which are similar to each other, differ substantially from those of the vastus intermedius muscle. Application of the results to jumping showed that bi-articular rectus femoris and biceps femoris muscles, which are antagonists, both contract eccentrically early in the push off phase and concentrically in last part of this phase.     

Inefficient use of inverted pendulum mechanism during quadrupedal walking in the Japanese macaque

In animal walking, the gravitational potential and kinetic energy of the center of mass (COM) fluctuates out-of-phase to reduce the energetic cost of locomotion via an inverted pendulum mechanism, and, in canine quadrupedal walking, up to 70% of the mechanical energy can be recovered. However, the rate of energy recovery for quadrupedal walking in primates has been reported to be comparatively lower. The present study analyzed fluctuations in the potential and kinetic energy of the COM during quadrupedal walking in the Japanese macaque to clarify the mechanisms underlying this inefficient utilization of the inverted pendulum mechanism in primates. Monkeys walked on a wooden walkway at a self-selected speed, and ground reaction forces were measured, using a force platform, to calculate patterns of mechanical energy fluctuation and rates of energy recovery. Our results demonstrated that rates of energy recovery for quadrupedal walking in Japanese macaques were approximately 30–50%, much smaller than those reported for dogs. Comparisons of the patterns of mechanical energy fluctuation suggested that the potential and kinetic energies oscillated relatively more in-phase, and amplitudes did not attain near equality during quadrupedal walking in Japanese macaques, possibly because of greater weight support (reaction force) of the hindlimbs and more protracted forelimbs at touchdown in the Japanese macaque, two of the three commonly accepted locomotor characteristics distinguishing primates from non-primate mammals.     

Lateral intermuscular septum of the thigh and short head of the biceps femoris muscle: an anatomic investigation with new clinical applications.

An anatomic study was performed to reappraise the vasculature of the lateral intermuscular septum of the thigh and muscles associated with it using 12 preserved cadaver legs. Several possible new clinical applications of the lateral intermuscular septum and the short head of the biceps femoris were identified as follows: (1) short head of biceps femoris muscle or musculoseptal flap based on the second and/or third profunda perforating vessels, or based on the superior lateral genicular vessels, with or without the iliotibial tract and the deep fascia, and with or without the motor nerve of the short head; (2) transverse extension of the fascial portion of the tensor fasciae latae muscle or musculocutaneous flap to include the lateral intermuscular septum; (3) combination use of items 1 and 2, above; and (4) free septofascial graft using the lateral intermuscular septum and iliotibial tract.It is anticipated that the distally based short head of the biceps femoris muscle flap will be an additional option for repairing defects around the knee, and that a free short head of the biceps femoris muscle flap based on the profunda femoris perforating vessels will be useful in functional reconstruction such as reanimation of the paralyzed face. The lateral intermuscular septum can be incorporated into the short head of biceps femoris muscle flap or into the tensor fasciae latae flap, and it also can be used as a free fascial graft. Functional deficit resulting from harvesting the short head of the biceps femoris and the lateral intermuscular septum is minimal, and donor wound at the lateral lower thigh seems to be acceptable.     

Reliability of leg muscle electromyography in vertical jumping

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis. biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.     

Segment and joint angles of hind limb during bipedal and quadrupedal walking of the bonobo (Pan paniscus)

We describe segment angles (trunk, thigh, shank, and foot) and joint angles (hip, knee, and ankle) for the hind limbs of bonobos walking bipedally ("bent-hip bent-knee walking," 17 sequences) and quadrupedally (33 sequences). Data were based on video recordings (50 Hz) of nine subjects in a lateral view, walking at voluntary speed. The major differences between bipedal and quadrupedal walking are found in the trunk, thigh, and hip angles. During bipedal walking, the trunk is approximately 33-41 degrees more erect than during quadrupedal locomotion, although it is considerably more bent forward than in normal human locomotion. Moreover, during bipedal walking, the hip has a smaller range of motion (by 12 degrees ) and is more extended (by 20-35 degrees ) than during quadrupedal walking. In general, angle profiles in bonobos are much more variable than in humans. Intralimb phase relationships of subsequent joint angles show that hip-knee coordination is similar for bipedal and quadrupedal walking, and resembles the human pattern. The coordination between knee and ankle differs much more from the human pattern. Based on joint angles observed throughout stance phase and on the estimation of functional leg length, an efficient inverted pendulum mechanism is not expected in bonobos.     

Energy expenditure of bipedal walking is higher than that of quadrupedal walking in Japanese macaques

The authors previously compared energetic costs of bipedal and quadrupedal walking in bipedally trained macaques used for traditional Japanese monkey performances (Nakatsukasa et al. 2004 Am. J. Phys. Anthropol. 124:248-256). These macaques used inverted pendulum mechanics during bipedal walking, which resulted in an efficient exchange of potential and kinetic energy. Nonetheless, energy expenditure during bipedal walking was significantly higher than that of quadrupedal walking. In Nakatsukasa et al. (2004 Am. J. Phys. Anthropol. 124:248-256), locomotor costs were measured before subjects reached a steady state due to technical limitations. The present investigation reports sequential changes of energy consumption during 15 min of walking in two trained macaques, using carbon dioxide production as a proxy of energy consumption, as in Nakatsukasa et al. (2004 Am. J. Phys. Anthropol. 124:248-256). Although a limited number of sessions were conducted, carbon dioxide production was consistently greater during bipedal walking, with the exception of some irregularity during the first minute. Carbon dioxide production gradually decreased after 1 min, and both subjects reached a steady state within 10 min. Energy expenditure during bipedalism relative to quadrupedalism differed between the two subjects. It was considerably higher (140% of the quadrupedal walking cost) in one subject who walked with more bent-knee, bent-hip gaits. This high cost strongly suggests that ordinary macaques, who adopt further bent-knee, bent-hip gaits, consume a far greater magnitude of energy during bipedal walking.     

Electromyography of back muscles during quadrupedal and bipedal walking in primates

Despite the extensive electromyographic research that has addressed limb muscle function during primate quadrupedalism, the role of the back muscles in this locomotor behavior has remained undocumented. We report here the results of an electromyographic (EMG) analysis of three intrinsic back muscles (multifidus, longissimus, and iliocostalis) in the baboon (Papio anubis), chimpanzee (Pan troglodytes), and orangutan (Pongo pygmaeus) during quadrupedal walking. The recruitment patterns of these three back muscles are compared to those reported for the same muscles during nonprimate quadrupedalism. In addition, the function of the back muscles during quadrupedalism and bipedalism in the two hominoids is compared. Results indicate that the back muscles restrict trunk movements during quadrupedalism by contracting with the touchdown of one or both feet, with more consistent activity associated with touchdown of the contralateral foot. Moreover, despite reported differences in their gait preferences and forelimb muscle EMG patterns, primates and nonprimate mammals recruit their back muscles in an essentially similar fashion during quadrupedal walking. These quadrupedal EMG patterns also resemble those reported for chimpanzees, gibbons and humans (but not orangutans) walking bipedally. The fundamental similarity in back muscle function across species and locomotor behaviors is consistent with other data pointing to conservatism in the evolution of the neural control of tetrapod limb movement, but does not preclude the suggestion (based on forelimb muscle EMG and spinal lesion studies) that some aspects of primate neural circuitry are unique. © 1994 Wiley-Liss, Inc.     

Voluntary bipedal walking of infant chimpanzees

The voluntary bipedal walking of infant chimpanzees was studied by the analysis of foot force and by motion analysis. The infants were trained to locomote on a level platform without any restrictions on the locomotor pattern. The voluntary bipedal walking was compared with the other types of locomotion at the same age and with the trained bipedal walking performed by other chimpanzees, including adult chimpanzees. The characteristics of voluntary bipedal walking in the infant until one year of age were: (1) high-speed walking with short cycle duration; (2) short stance phase duration; (3) small braking component of the preceding leg and large acceleration of the following leg; (4) one downward peak in the vertical component; and (5) a relatively small transverse component. Bipedal walking usually continued for less than one second and ended in quadrupedal locomotion. During walking, the preceding foot touched the floor, heel first, as in the case of older chimpanzees and humans. At this age, bipedal walking was similar to high-speed locomotion. The voluntary bipedal walking of the two-year-old and frour-yearold chimpanzees was characterized as follows: (1) slower speed than during quadrupedal locomotion, (2) relatively long periods and distances; (3) well balanced accelerating and braking components; and (4) a vertical component showing two downward peaks and a trough in between during numerous trials. The last characteristic means that the body center of gravity is higher in the single stance phase, just as in the bipedal walkinbg of the adult chimpanzees and humans. The bipedal walking of infant chimpanzees was discussed in comparison with the walking of humans, including infants.     

Development of an anatomically based whole‐body musculoskeletal model of the Japanese macaque (Macaca fuscata)

We constructed a three‐dimensional whole‐body musculoskeletal model of the Japanese macaque (Macaca fuscata) based on computed tomography and dissection of a cadaver. The skeleton was modeled as a chain of 20 bone segments connected by joints. Joint centers and rotational axes were estimated by joint morphology based on joint surface approximation using a quadric function. The path of each muscle was defined by a line segment connecting origin to insertion through an intermediary point if necessary. Mass and fascicle length of each were systematically recorded to calculate physiological cross‐sectional area to estimate the capacity of each muscle to generate force. Using this anatomically accurate model, muscle moment arms and force vectors generated by individual limb muscles at the foot and hand were calculated to computationally predict muscle functions. Furthermore, three‐dimensional whole‐body musculoskeletal kinematics of the Japanese macaque was reconstructed from ordinary video sequences based on this model and a model‐based matching technique. The results showed that the proposed model can successfully reconstruct and visualize anatomically reasonable, natural musculoskeletal motion of the Japanese macaque during quadrupedal/bipedal locomotion, demonstrating the validity and efficacy of the constructed musculoskeletal model. The present biologically relevant model may serve as a useful tool for comprehensive understanding of the design principles of the musculoskeletal system and the control mechanisms for locomotion in the Japanese macaque and other primates. Am J Phys Anthropol, 2009. © 2008 Wiley‐Liss, Inc.     

Bipedal versus Quadrupedal Hind Limb and Foot Kinematics in a Captive Sample of <Emphasis Type="Italic">Papio anubis:</Emphasis> Setup and Preliminary Results

Setups that integrate both kinematics and morpho-functional investigations of a single sample constitute recent developments in the study of nonhuman primate bipedalisms. We introduce the integrated setup built at the Primatology Station of the French National Centre for Scientific Research (CNRS), which allows analysis of both bipedal and quadrupedal locomotion in a population of 55–60 captive olive baboons. As a first comparison, we present the hind limb kinematics of both locomotor modalities in 10 individuals, focusing on the stance phase. The main results are: 1) differences in bipedal and quadrupedal kinematics at the hip, knee, and foot levels; 2) a variety of foot contacts to the ground, mainly of semiplantigrade type, but also of plantigrade type; 3) equal variations between bipedal and quadrupedal foot angles; 4) the kinematics of the foot joints act in coordinated and stereotyped manners, but are triggered differently according to whether the support is bipedal or quadrupedal. Although very occasionally realized, the bipedal walk of olive baboon appears to be a habitual and nonerratic locomotor modality.     

An electromyographic analysis of hindlimb function in Alligator during terrestrial locomotion

The neuromuscular control of the hindlimb of American alligators (Alligator mississippiensis) walking on a treadmill was analyzed using simultaneous electromyography (EMG) and cineradiography. EMG and kinematic data were integrated with myological information to discern the interplay of muscles mediating hip and knee movement during the high walk. Twelve muscles, subdivided into 23 individual heads, cross the hip joint of Alligator. Activity patterns of 12 heads of 11 hip muscles and one knee muscle were recorded and quantified. An additional five heads from four muscles were recorded in single individuals. During the stance phase, the caudofemoralis longus prevents hip flexion and actively shortens to retract the femur through an arc of 60–80°. At the same time, the adductor femoris 1 and pubo-ischio-tibialis control femoral abduction. The knee is extended 30–40° during stance by contraction of the femoro-tibialis internus. These stance phase muscles often produce discontinuous, periodic EMG signals within their normal burst profile. In late stance and early swing, the ilio-fibularis and the pubo-ischio-tibialis are responsible for flexing the knee. The limb is protracted by the pubo-ischio-femoralis internus 2 and pubo-ischio-femoralis externus 2, which flex the hip. The ilio-femoralis abducts the limb during swing to suspend it above the tread. The role of the ambiens 1, which is active in midswing, is unclear. The ilio-tibialis 2, flexor-tibialis externus and flexor-tibialis internus 2 yield sporadic, low amplitude EMGs; these muscles are recruited at a very low level, if at all, during the slow high walk. Although EMGs do not conclusively delineate muscle function, activity patterns are particularly helpful in elucidating the complex interaction of muscular heads in this system. J. Morphol. 234:197–212, 1997. © 1997 Wiley-Liss, Inc.     

Contributions of muscles and passive dynamics to swing initiation over a range of walking speeds

Stiff-knee gait is a common walking problem in cerebral palsy characterized by insufficient knee flexion during swing. To identify factors that may limit knee flexion in swing, it is necessary to understand how unimpaired subjects successfully coordinate muscles and passive dynamics (gravity and velocity-related forces) to accelerate the knee into flexion during double support, a critical phase just prior to swing that establishes the conditions for achieving sufficient knee flexion during swing. It is also necessary to understand how contributions to swing initiation change with walking speed, since patients with stiff-knee gait often walk slowly. We analyzed muscle-driven dynamic simulations of eight unimpaired subjects walking at four speeds to quantify the contributions of muscles, gravity, and velocity-related forces (i.e. Coriolis and centrifugal forces) to preswing knee flexion acceleration during double support at each speed. Analysis of the simulations revealed contributions from muscles and passive dynamics varied systematically with walking speed. Preswing knee flexion acceleration was achieved primarily by hip flexor muscles on the preswing leg with assistance from biceps femoris short head. Hip flexors on the preswing leg were primarily responsible for the increase in preswing knee flexion acceleration during double support with faster walking speed. The hip extensors and abductors on the contralateral leg and velocity-related forces opposed preswing knee flexion acceleration during double support.     

Fiber architecture of the intrinsic muscles of the shoulder and arm in semiterrestrial and arboreal guenons

The internal organization of myofibers and connective tissues has important physiologic implications for muscle function and for naturalistic behavior. In this study of forelimb muscle morphology and primate locomotion, fiber architecture is examined in the intrinsic muscles of the shoulder (musculi deltoideus, infraspinatus, supraspinatus, subscapularis, teres major, and t. minor) and arm (m. coracobrachialis, biceps brachii, brachialis, and triceps brachii) in the semiterrestrial vervets (Chlorocebus aethiops) and arboreal red-tailed guenons (Cercopithecus ascanius). Wet weights and lengths of whole muscles, lengths of fasciculi and their associated proximal and distal tendons, and angles of pinnation were measured to estimate morphologic correlates of physiologic properties of individual muscles: force, velocity/excursion, energy expense, and relative isometric or isotonic contraction. Neither mean total-shoulder:total-arm ratios for muscle mass nor total reduced physiological cross-sectional area exhibited significant (P < 0.05) interspecific differences, thus emphasizing the importance of fine-tuning musculoskeletal analyses by the data collected here. The results generally support those previously published for quadriceps femoris and triceps surae of the hind limb in these species (Anapol and Barry [1996] Am. J. Phys. Anthropol. 99:429-447). The fiber architecture of the semiterrestrial vervets is largely suited for higher velocity while running on the ground. By contrast, the architectural configuration of red-tailed monkeys implies relatively isometric muscle contraction and passive storage of elastic strain energy for exploitation of the compliant canopy, where substrate components are situated beneath the sagittal plane of the animal. With respect to relative distribution of maximum potential force output among muscles of either shoulder or arm groups in these otherwise hind limb-dominated quadrupedal primates, statistically significant interspecific differences are best interpreted in light of braking, climbing, and, for vervets, the transition between ground and canopy.The interspecific differences shown here for the intrinsic muscles of the shoulder and arm underscore the significance of intramuscular morphology in reconciling structure and function with regard to locomotor behavior. Its analysis and interpretation lend support to consideration of "semiterrestrial" as a bona fide locomotor category uniquely different from what is practiced by dedicated arboreal and terrestrial quadrupeds that occasionally visit the habitat of one another. Data from a more committed terrestrial species would clarify this enigma.     

Differential atrophy of the postero-lateral hip musculature during prolonged bedrest and the influence of exercise countermeasures

As part of the 2nd Berlin BedRest Study (BBR2-2), we investigated the pattern of muscle atrophy of the postero-lateral hip and hamstring musculature during prolonged inactivity and the effectiveness of two exercise countermeasures. Twenty-four male subjects underwent 60 days of head-down tilt bedrest and were assigned to an inactive control (CTR), resistive vibration exercise (RVE), or resistive exercise alone (RE) group. Magnetic resonance imaging (MRI) of the hip and thigh was taken before, during, and at end of bedrest. Volume of posterolateral hip and hamstring musculature was calculated, and the rate of muscle atrophy and the effect of countermeasure exercises were examined. After 60 days of bedrest, the CTR group showed differential rates of muscle volume loss (F = 21.44; P ≤ 0.0001) with fastest losses seen in the semi-membranosus, quadratus femoris and biceps femoris long head followed by the gluteal and remaining hamstring musculature. Whole body vibration did not appear to have an additional effect above resistive exercise in preserving muscle volume. RE and RVE prevented and/or reduced muscle atrophy of the gluteal, semi-membranosus, and biceps femoris long head muscles. Some muscle volumes in the countermeasure groups displayed faster recovery times than the CTR group. Differential atrophy occurred in the postero-lateral hip musculature following a prolonged period of unloading. Short-duration high-load resistive exercise during bedrest reduced muscle atrophy in the mono-articular hip extensors and selected hamstring muscles. Future countermeasure design should consider including isolated resistive hamstring curls to target this muscle group and reduce the potential for development of muscle imbalances.