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Current knowledge of the physiological range of motion (ROM) in the canine axial system during locomotion is relatively limited. This is particularly problematic because dogs with back-related dysfunction frequently present for routine consultations. To collect detailed kinematic information and describe the three-dimensional motions of the pelvis and the lumbar spine (i.e. intervertebral joints S1/L7-L2/L1), we recorded ventro-dorsal and latero-lateral X-ray videos of three walking and trotting dogs and reconstructed their pelvic and intervertebral motions using X-ray reconstruction of moving morphology and scientific rotoscoping. Pelvic roll displayed a monophasic motion pattern and the largest ROM with on average 13° and 11° during walking and trotting, respectively. Pelvic yaw had the smallest ROM with on average 5° (walk) and 6° (trot). A biphasic pattern was observed for pelvic pitch with a mean ROM of 8°. At both gaits, the greatest intervertebral motions occurred either in S1/L7 or L7/L6. The intervertebral motions were mono- or biphasic in the horizontal and the transverse body planes and biphasic in the sagittal plane. Cranial to L6/5, the ROM tended to decrease from 3° to

Limb amputation often represents the only treatment option for canine patients with certain diseases or injuries of the appendicular system. Previous studies have investigated adaptations to tripedal locomotion in dogs but there is a lack of understanding of biomechanical compensatory mechanisms. This study evaluated the kinematic differences between quadrupedal and tripedal locomotion in nine healthy dogs running on a treadmill. The loss of the right pelvic limb was simulated using an Ehmer sling. Kinematic gait analysis included spatio-temporal comparisons of limb, joint and segment angles of the remaining pelvic and both thoracic limbs. The following key parameters were compared between quadrupedal and tripedal conditions: angles at touch-down and lift-off, minimum and maximum joint angles, plus range of motion. Significant differences in angular excursion were identified in several joints of each limb during both stance and swing phases. The most pronounced differences concerned the remaining pelvic limb, followed by the contralateral thoracic limb and, to a lesser degree, the ipsilateral thoracic limb. The thoracic limbs were, in general, more retracted, consistent with pelvic limb unloading and previous observations of bodyweight re-distribution in amputees. Proximal limb segments showed more distinct changes than distal ones. Particularly, the persistently greater anteversion of the pelvis probably affects the axial system. Overall, tripedal locomotion requires concerted kinematic adjustments of both the appendicular and axial systems, and consequently preventive, therapeutic and rehabilitative care of canine amputees should involve the whole musculoskeletal apparatus.

To gain insight into the adaptive mechanisms to tripedal locomotion and increase understanding of the biomechanical consequences of limb amputation, this study investigated kinetic and temporal gait parameters in dogs before and after the loss of a hindlimb was simulated. Nine clinically sound Beagle dogs trotted on an instrumented treadmill and the ground reaction forces as well as the footfall patterns were compared between quadrupedal and tripedal locomotion. Stride and stance durations decreased significantly in all limbs when the dogs ambulated tripedally, while relative stance duration increased. Both vertical and craniocaudal forces were significantly different in the remaining hindlimb. In the forelimbs, propulsive force increased in the contralateral and decreased in the ipsilateral limb, while the vertical forces were unchanged (except for mean force in the contralateral limb). Bodyweight was shifted to the contralateral and cranial body side so that each limb bore ~33% of the dog's bodyweight. The observed changes in the craniocaudal forces and the vertical impulse ratio between the fore- and hindlimbs suggest that a nose-up pitching moment occurs during the affected limb pair's functional step. To regain pitch balance for a given stride cycle, a nose-down pitching moment is exerted when the intact limb pair supports the body. These kinetic changes indicate a compensatory mechanism in which the unaffected diagonal limb pair is involved. Therefore, the intact support pair of limbs should be monitored closely in canine hindlimb amputees.

Weight support patterns vary widely among mammals. Differences in how much of the body weight is supported by the fore- versus the hind-limbs are well documented among and within species. Intraindividual variation due to ontogenetic processes has been studied in several hindlimb-dominated species and consistently showed a caudal shift in the limbs' support roles. We hypothesized that forelimb-dominated species exhibit a cranial shift in their support pattern and tested this hypothesis by examining the vertical ground reaction forces in growing dogs. Six male Beagle siblings were studied from 9 to 51 postnatal weeks (PW) of age while they trotted on an instrumented treadmill. Ontogenetic shifting in fore-to-hind support was evaluated using vertical force ratios (i.e., peak and impulse) as well as the stance time ratio of the fore- and the hind-limbs. Because morphological and kinematic characteristics influence weight support patterns, changes in body shape (i.e., trunk shape), and average limb position were determined. As in adult dogs, the forelimbs carried a greater proportion of the body weight than the hindlimbs at all ages. When the dogs were younger, peak vertical force occurred earlier during stance in the hindlimbs but not the forelimbs. Both the increasing ratio of the vertical force and the increasing ratio of the stance times indicate an increasing weight support by the forelimbs (i.e., 59% at PW9 vs. 63% at PW51). The observed ontogenetic changes in trunk shape and average limb angle were consistent with this cranial shift in weight support. J. Exp. Zool. 321A:254–264, 2014. © 2014 Wiley Periodicals, Inc.

Craniate animals – vertebrates and their jawless sister taxa – have evolved a body axis with powerful muscles, a distributed nervous system to control those muscles, and an endoskeleton that starts at the head and ends at the caudal fin. The body axis undulates, bends, twists, or holds firm, depending on the behavior. In this introduction to the special issue on axial systems and their actuation, we provide an overview of the latest research on how the body axis functions, develops, and evolves. Based on this research, we hypothesize that the body axis of craniates has three primary, post-cranial modules: precaudal, caudal, and tail. The term “module” means a portion of the body axis that functions, develops, and evolves in relative independence from other modules; “relative independence” means that structures and processes within a module are more tightly correlated in function, development, and behavior than the same processes are among modules.

Human back muscles have been classified as local stabilizers, global stabilizers and global mobilizers. This concept is supported by the distribution of slow and fast muscle fibres in quadrupedal mammals, but has not been evaluated for humans because detailed information on the fibre type composition of their perivertebral musculature is rare. Moreover, such information is derived from spot samples, which are assumed to be representative for the respective muscle. In accordance with the proposed classification, numerous studies in animals indicate great differences in the fibre distribution within and among the muscles due to fibre type regionalization. The aims of this study were to (1) qualitatively explore the applicability of the proposed functional classification for human back muscles by studying their fibre type composition and (2) evaluate the representativeness of spot sampling techniques. For this, the fibre type distribution of the whole lumbar perivertebral musculature of two male cadavers was investigated three-dimensionally using immunohistochemistry. Despite great local variations (e.g., among fascicles), all muscles were composed of about 50% slow and 50% fast fibres. Thus, contradicting the concepts of lumbar muscle function, no functional differentiation of the muscles was observed in our study of the muscle contractile properties. The great similarity in fibre composition among the muscles equips each muscle equally well for a broad range of tasks and therefore has the potential to allow for great functional versatility of the human back musculature. Spot samples do not prove to be representative for the whole muscle. The great intraspecific variability observed previously in single-spot samples is potentially misleading.

This study evaluated adaptations in vertical force and temporal gait parameters to hind limb lameness in walking and trotting dogs. Eight clinically normal adult Beagles were allowed to ambulate on an instrumented treadmill at their preferred speed while the ground reaction forces were recorded for all limbs before and after a moderate, reversible, hind limb lameness was induced. At both gaits, vertical force was decreased in the ipsilateral and increased in the contralateral hind limb. While peak force increased in the ipsilateral forelimb, no changes were observed for mean force and impulse when the dogs walked or trotted. In the contralateral forelimb, the peak force was unchanged, but the mean force significantly increased during walking and trotting; vertical impulse increased only during walking. Relative stance duration increased in the ipsilateral hind limb when the dogs trotted. In the contralateral fore and hind limbs, relative stance duration increased during walking and trotting, but decreased in the ipsilateral forelimb during walking. Analysis of load redistribution and temporal gait changes during hind limb lameness showed that compensatory mechanisms were similar regardless of gait. The centre of mass consistently shifted to the contralateral body side and cranio-caudally to the side opposite the affected limb. These biomechanical changes indicate substantial short- and long-term effects of hind limb lameness on the musculoskeletal system.

Compared to anurans from other families, landings of toads (Bufonidae) during saltation appear well coordinated and the initial landing impact is absorbed exclusively by the forelimbs. Although the forelimbs and particularly the pectoral girdle have been suggested to be important for shock absorption, the functional roles of its various elements have not been evaluated in detail. This study addresses open questions regarding the kinematics of the forelimbs during landing in Rhinella marina using X-ray reconstruction of moving morphology and scientific rotoscoping. The kinematic analysis clearly showed that in addition to motions in the shoulder and elbow joints, substantial movements of the pectoral girdle in toto as well as of its elements relative to each other do occur during landing. The pectoral girdle showed first and foremost rotations about its latero-lateral axis as well as dorso-ventral translations relative to the spine. Our results quantify the extent of flexion and extension in the suprascapula-scapular synchondrosis during landing. Forelimb kinematics in R. marina differed from that of other anurans in starting elbow extension relatively early during the landing process, which likely prevents the chest from contacting the ground. Furthermore, the animal regains an upright and ready-to-hop-again position quickly and the recovery phase is short compared to other anurans. Humeral kinematics and anatomy confirm that the glenohumeral interlocking mechanism guides the humerus during the initial landing phase. Cranio-ventral ridges on the humeral head and the paraglenoid cartilage interlock in anteverted and slightly retroverted humeral positions. This occurs at the beginning of the landing. When interlocked, adduction/abduction as well as long-axis rotation of the humerus are restricted. During the course of landing, the humerus retroverts and is gradually freed from interlocking restrictions due to a smoother relief at the caudal aspect of the humeral head.

Objective—To evaluate the load redistribution mechanisms in walking and trotting dogs with induced forelimb lameness. Animals—7 healthy adult Beagles. Procedures—Dogs walked and trotted on an instrumented treadmill to determine control values for peak and mean vertical force as well as verticle impulse for all 4 limbs. A small sphere was attached to the ventral pad of the right forelimb paw to induce a reversible lameness, and recordings were repeated for both gaits. Additionally, footfall patterns were assessed to test for changes in temporal gait variables. Results—During walking and trotting, peak and mean vertical force as well as vertical impulse were decreased in the ipsilateral forelimb, increased in the contralateral hind limb, and remained unchanged in the ipsilateral hind limb after lameness was induced. All 3 variables were increased in the contralateral forelimb during trotting, whereas only mean vertical force and vertical impulse were increased during walking. Stance phase duration increased in the contralateral forelimb and hind limb during walking but not during trotting. Conclusions and Clinical Relevance—Analysis of the results suggested that compensatory load redistribution mechanisms in dogs depend on the gait. All 4 limbs should be evaluated in basic research and clinical studies to determine the effects of lameness on the entire body. Further studies are necessary to elucidate specific mechanisms for unloading of the affected limb and to determine the long-term effects of load changes in animals with chronic lameness.

Differences in rhythmicity (relative variance in cycle period) among mammal, fish, and lizard feeding systems have been hypothesized to be associated with differences in their sensorimotor control systems. We tested this hypothesis by examining whether the locomotion of tachymetabolic tetrapods (birds and mammals) is more rhythmic than that of bradymetabolic tetrapods (lizards, alligators, turtles, salamanders). Species averages of intraindividual coefficients of variation in cycle period were compared while controlling for gait and substrate. Variance in locomotor cycle periods is significantly lower in tachymetabolic than in bradymetabolic animals for datasets that include treadmill locomotion, non-treadmill locomotion, or both. When phylogenetic relationships are taken into account the pooled analyses remain significant, whereas the non-treadmill and the treadmill analyses become nonsignificant. The co-occurrence of relatively high rhythmicity in both feeding and locomotor systems of tachymetabolic tetrapods suggests that the anatomical substrate of rhythmicity is in the motor control system, not in the musculoskeletal components.

The perivertebral musculature of lizards is critical for the stabilization and the mobilization of the trunk during locomotion. Some trunk muscles are also involved in ventilation. This dual function of trunk muscles in locomotion and ventilation leads to a biomechanical conflict in many lizards and constrains their ability to breathe while running (“axial constraint”) which likely is reflected by their high anaerobic scope. Furthermore, different foraging and predator-escape strategies were shown to correlate with the metabolic profile of locomotor muscles in lizards. Because knowledge of muscle's fiber-type composition may help to reveal a muscle's functional properties, we investigated the distribution pattern of muscle fiber types in the perivertebral musculature in two small lizard species with a generalized body shape and subjected to the axial constraint (Dipsosaurus dorsalis, Acanthodactylus maculatus) and one species that circumvents the axial constraint by means of gular pumping (Varanus exanthematicus). Additionally, these species differ in their predator-escape and foraging behaviors. Using refined enzyme-histochemical protocols, muscle fiber types were differentiated in serial cross-sections through the trunk, maintaining the anatomical relationships between the skeleton and the musculature. The fiber composition in Dipsosaurus and Acanthodactylus showed a highly glycolytic profile, consistent with their intermittent locomotor style and reliance on anaerobic metabolism during activity. Because early representatives of diapsids resemble these two species in several postcranial characters, we suggest that this glycolytic profile represents the plesiomorphic condition for diapsids. In Varanus, we found a high proportion of oxidative fibers in all muscles, which is in accordance with its high aerobic scope and capability of sustained locomotion. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.

SUMMARYThe extrinsic limb muscles perform locomotor work and must adapt their activity to changes in gait and locomotor speed, which can alter the work performed by, and forces transmitted across, the proximal fulcra of the limbs where these muscles operate. We recorded electromyographic activity of 23 extrinsic forelimb and hindlimb muscles and one trunk muscle in dogs while they walked, trotted and galloped on a level treadmill. Muscle activity indicates that the basic functions of the extrinsic limb muscles – protraction, retraction and trunk support – are conserved among gaits. The forelimb retains its strut-like behavior in all gaits, as indicated by both the relative inactivity of the retractor muscles (e.g. the pectoralis profundus and the latissimus dorsi) during stance and the protractor muscles (e.g. the pectoralis superficialis and the omotransversarius) in the first half of stance. The hindlimb functions as a propulsive lever in all gaits, as revealed by the similar timing of activity of retractors (e.g. the biceps femoris and the gluteus medius) during stance. Excitation increased in many hindlimb muscles in the order walk–trot–gallop, consistent with greater propulsive impulses in faster gaits. Many forelimb muscles, in contrast, showed the greatest excitation at trot, in accord with a shorter limb oscillation period, greater locomotor work performed by the forelimb and presumably greater absorption of collisional energy.

Humans are known to have energetically optimal walking and running speeds at which the cost to travel a given distance is minimized. We hypothesized that “optimal” walking and running speeds would also exist at the level of individual locomotor muscles. Additionally, because humans are 60–70% more economical when they walk than when they run, we predicted that the different muscles would exhibit a greater degree of tuning to the energetically optimal speed during walking than during running. To test these hypotheses, we used electromyography to measure the activity of 13 muscles of the back and legs over a range of walking and running speeds in human subjects and calculated the cumulative activity required from each muscle to traverse a kilometer. We found that activity of each of these muscles was minimized at specific walking and running speeds but the different muscles were not tuned to a particular speed in either gait. Although humans are clearly highly specialized for terrestrial locomotion compared with other great apes, the results of this study indicate that our locomotor muscles are not tuned to specific walking or running speeds and, therefore, do not maximize the economy of locomotion. This pattern may have evolved in response to selection to broaden the range of sustainable running speeds, to improve performance in motor behaviors not related to endurance locomotion, or in response to selection for both.

Different locomotor and postural demands are met partly due to the varying properties and proportions of the muscle fibre types within the skeletal muscles. Such data are therefore important in understanding the subtle relationships between morphology, function and behaviour. The triceps surae muscle group is of particular interest when studying our closest living relatives, the non-human great apes, as they lack a significant external Achilles tendon, crucial to running locomotion in humans and other cursorial species. The aim of this study, therefore, was to determine the proportions of type I (slow) and type II (fast) fibres throughout these muscles in chimpanzees and orangutans using immunohistochemistry. The orangutan had a higher proportion of type I fibres in all muscles compared with the chimpanzees, related to their slower, more controlled movements in their arboreal habitat. The higher proportion of type II fibres in the chimpanzees likely reflects a compromise between their need for controlled mobility when arboreal, and greater speed and power when terrestrial. Overall, the proportion of slow fibres was greater in the soleus muscle compared with the gastrocnemius muscles, and there was some evidence of proximal to distal and medial to lateral variations within some muscles. This study has shown that not only do orangutans and chimpanzees have very different muscle fibre populations that reflect their locomotor repertoires, but it also shows how the proportion of fibre types provides an additional mechanism by which the performance of a muscle can be modulated to suit the needs of a species.

A muscle's architecture, described by geometric variables such as fascicle pennation angles or lengths, plays a crucial role in its functionality. Usually, single parameters are used to estimate force vectors or lengthening rates, thereby assuming that they represent the architecture properly and are constant during contraction. To describe muscle architecture in more detail and compare relaxed and contracted states, we developed and validated a new approach. The m. soleus of the laboratory rat was shock-frozen while relaxed and under isometric contraction, reconstructed three-dimensionally from histological sections, and fascicle lengths, curvatures and pennation angles, as well as the shape of the aponeuroses were analysed. Remarkable differences in volume distribution and the shapes of the aponeuroses as well as locally varying changes in the fascicle architecture were observed. While the mean pennation angle increased by only 2° due to contraction, local changes of up to 4° were observed. Fascicle curvature increased in the distal but remained unchanged in the proximal parts. Our approach may help to identify functional subunits within the muscle, i.e., regions with homogeneous architectural properties. Our results are discussed regarding the input parameters essential for realistic muscle modelling and challenge maximum isometric force estimations that are based on the physiological cross-sectional area or the Hill-model.

SUMMARYThe extrinsic appendicular muscles of mammals have been suggested to impose parasagittal torques on the trunk that require recruitment of the oblique hypaxial muscles for stabilization. To determine if the recruitment of the protractors and retractors of the hindlimb are compatible with this hypothesis, we monitored changes in the recruitment of eleven muscles that span the hip joint to controlled manipulations of locomotor forces in trotting dogs. The results indicate that the primary retractor muscles of the hindlimb produce a small retraction moment at the hip joint early in the support phase during trotting at constant speed on a level surface. Thus, although the forelimb of dogs appears to function as a compliant strut, the hindlimb functions as a lever early in stance phase. Nevertheless, our results indicate that when dogs run at constant speed on a level surface a primary function of both the retractor and protractor muscles of the hindlimb is to produce swing phase of the limb. When the trotting dogs did net work in the fore–aft direction, by running uphill or downhill or by resisting a horizontally directed force, recruitment of the protractor and retractor muscles of the hip joint increased or decreased in the anticipated fashion. These observations are consistent with the hypothesis that recruitment of the oblique hypaxial muscles in trotting dogs function to stabilize the trunk against torques produced by protractor and retractor muscles of the hindlimb.

Der chronische unspezifische Ruckenschmerz ist ein zentrales Thema fur Patienten, Versicherer und Berufsgenossenschaften. Mit einer Praventivdiagnostik bestunde die Moglichkeit, fur einen momentan beschwerdefreien Menschen eine Prognose zu erstellen, mit welcher Wahrscheinlichkeit er einen chronischen unspezifischen Ruckenschmerz erleiden wird, wenn er sich nicht einer praventiven Masnahme unterzieht. Jedes Jahr erleiden 20% der Erwachsenen Ruckenschmerzen und 70–80% der Bevolkerung bekommen in ihrem Leben einmal oder mehrmals Ruckenschmerzen. Meist reduzieren sich die Beschwerden innerhalb der ersten sechs Wochen ohne medizinische Intervention oder verschwinden ganz. Nur in wenigen Fallen sind sie progredient, chronifizieren und verursachen erhebliche Kosten. Es gilt herauszufinden, ob eine Person zu einer Risikogruppe gezahlt werden kann, fur die zukunftig eine Chronifizierung des Ruckenschmerzes wahrscheinlich wird. Mit dem praventivdiagnostischen Ansatz sollte die Frage beantwortet werden konnen: Welche Subgruppe von Patienten mit chronischem Ruckenschmerz wird besonders von einer Ubungstherapie oder von kognitiven verhaltenstherapeutischen Ansatzen profitieren?

Alterations in muscle recruitment are key to the functional plasticity of the mammalian locomotor system. One particularly challenging situation quadrupeds may face is when the functionality of a limb is reduced or lost. To better understand how mammals manage in such situations and which muscular adaptations they exhibit when locomoting on three legs, we recorded the activity patterns of two limb and one back extensor muscle in nine dogs using surface electromyography. We compared the timing and the level of recruitment before and after the loss of a hindlimb was simulated. Both the intensity and the timing of the activity changed significantly in the m. vastus lateralis of the remaining hindlimb, consistent with this limb bearing a greater proportion of the body weight as well as with previously reported kinematic changes. In accordance with the greater body weight supported by the forelimbs, the m. triceps brachii showed first and foremost an increased level of excitation. The very asymmetrical changes in the timing and the level of activity in the m. longissimus dorsi reflects the highly asymmetrical functional requirements imposed on the trunk and the pelvis when one hindlimb is no longer involved in the production of locomotor work while the other hindlimb partially compensates the loss. Integration of our electromyographical findings with kinetic and kinematic results illustrates that dogs exhibited a well-coordinated response to the functional requirements of tripedalism and underlines the importance of moment-to-moment modulation in muscular recruitment for the functional plasticity of the mammalian locomotor system. J. Exp. Zool. 323A: 506–515, 2015. © 2015 Wiley Periodicals, Inc.

Using a biomechanical model and experimental data the self-stabilising behaviour of antagonistic trunk muscles was analyzed. The biomechanical model is constituted of a pair of antagonistic Hill-type muscles, their geometric arrangement with respect to the spine, and the instantaneous centre of rotation in frontal plane. Using Ljapunov's theory, the stability of certain motion and loading situations was analyzed. Applying a sensitivity analysis, the influence of different muscle properties and the geometric arrangement on stability was investigated. The simulations revealed that the stability of spinal movements depended primarily on the geometrical arrangement of muscles and the position of the centre of rotation of the spine, the latter was affected in turn by the activities of the profound muscles. To stabilize the situations simulated oblique muscle arrangements were necessary. In order to define an instantaneous centre of rotation in the lower region of the spine negative attachment angles (medio-lateral decline) of muscles were necessary, corresponding to the real anatomy of obliquus externus muscles. More cranially located instantaneous centres of rotation required positive attachment angles for stability, corresponding to obliquus internus or multifidus muscles. Furthermore, the fibre-type distribution of muscles influenced the stability of the system, i.e. a high percentage of fast-twitch-fibres supported the stabilisation. Conclusions drawn from the simulations were supported by experimental data. Sudden loads and quick-release perturbations with two different amplitudes were applied to the upper body of ten male subjects. In comparison to sudden load situations preactivation of muscles due to an external load, i.e. quick-release perturbation, led to significantly less dependency of the amplitude of deflection on the amplitude of the perturbation. This observation relates to the self-stabilising properties of the musculoskeletal system. In conclusion, training seems to be advantageous if directed towards not only enhancing the endurance capacity of the muscles, but also increasing the cross-sectional area of oblique fast-twitch-fibres. Training should also improve the co-ordination of deep and superficial trunk muscles. These findings may influence physiotherapy and training programs for low back pain patients.

Item does not contain fulltext Multichannel surface EMG recordings of a multiheaded skeletal muscle during cyclic locomotion combined with cineradiography were analysed in a chronic experiment. The resulting detailed two-dimensional activation pattern from the long and lateral triceps brachii heads of the rat during treadmill locomotion were combined with gait characteristics and fibre typing of the muscle. Shortly before ground contact of the forelimb, maximum muscle activity was found in the proximal part of the long head of the muscle. During the stance phase maximum activity was observed in the proximal part of the lateral head. The frequency dependent behaviour of cross-covariance functions over both muscle heads confirmed this selective shift in activation. In the lateral triceps brachii head of the investigated rats, exclusively type II fibres were found. In the long head the frequency of type I fibres was the highest in the deep muscle layers, proximally more than distally, whereas type II fibres were dominant in more superficial muscle layers. A combination of physiological and histological findings supports an anticipating mechanism whereby fine-tuning of the vertical foot down manoeuvre is mainly achieved by the (type I fibre dominated) proximal deep compartment of the biarticular long triceps brachii head and force generation is predominantly executed by the monoarticular lateral triceps brachii head.

The axial musculoskeletal system is important for the static and dynamic control of the body during both locomotor and non-locomotor behaviour. As a consequence, major evolutionary changes in the positional habits of a species are reflected by morpho-functional adaptations of the axial system. Because of the remarkable phenotypic plasticity of muscle tissue, a close relationship exists between muscle morphology and function. One way to explore major evolutionary transitions in muscle function is therefore by comparative analysis of fibre type composition. In this study, the three-dimensional distribution of slow and fast muscle fibres was analysed in the lumbar perivertebral muscles of two lemuriform (mouse lemur, brown lemur) and four hominoid primate species (white-handed gibbon, orangutan, bonobo, chimpanzee) in order to develop a plausible scenario for the evolution of the contractile properties of the axial muscles in hominoids and to discern possible changes in muscle physiology that were associated with the evolution of orthogrady. Similar to all previously studied quadrupedal mammals, the lemuriform primates in this study exhibited a morpho-functional dichotomy between deep slow contracting local stabilizer muscles and superficial fast contracting global mobilizers and stabilizers and thus retained the fibre distribution pattern typical for quadrupedal non-primates. In contrast, the hominoid primates showed no regionalization of the fibre types, similar to previous observations in Homo. We suggest that this homogeneous fibre composition is associated with the high functional versatility of the axial musculature that was brought about by the evolution of orthograde behaviours and reflects the broad range of mechanical demands acting on the trunk in orthograde hominoids. Because orthogrady is a derived character of euhominoids, the uniform fibre type distribution is hypothesized to coincide with the evolution of orthograde behaviours.

Weight support patterns vary widely among mammals. Differences in how much of the body weight is supported by the fore- versus the hind-limbs are well documented among and within species. Intraindividual variation due to ontogenetic processes has been studied in several hindlimb-dominated species and consistently showed a caudal shift in the limbs' support roles. We hypothesized that forelimb-dominated species exhibit a cranial shift in their support pattern and tested this hypothesis by examining the vertical ground reaction forces in growing dogs. Six male Beagle siblings were studied from 9 to 51 postnatal weeks (PW) of age while they trotted on an instrumented treadmill. Ontogenetic shifting in fore-to-hind support was evaluated using vertical force ratios (i.e., peak and impulse) as well as the stance time ratio of the fore- and the hind-limbs. Because morphological and kinematic characteristics influence weight support patterns, changes in body shape (i.e., trunk shape), and average limb position were determined. As in adult dogs, the forelimbs carried a greater proportion of the body weight than the hindlimbs at all ages. When the dogs were younger, peak vertical force occurred earlier during stance in the hindlimbs but not the forelimbs. Both the increasing ratio of the vertical force and the increasing ratio of the stance times indicate an increasing weight support by the forelimbs (i.e., 59% at PW9 vs. 63% at PW51). The observed ontogenetic changes in trunk shape and average limb angle were consistent with this cranial shift in weight support.

Many training concepts take muscle properties such as contraction speed or muscle topography into account to achieve an optimal training outcome. Thus far, the internal architecture of muscles has largely been neglected, although it is well known that parameters such as pennation angles or the lengths of fascicles but also the proportions of fleshy and tendinous fascicle parts have a major impact on the contraction behaviour of a muscle. Here, we present the most detailed description of the intramuscular fascicle architecture of the human perivertebral muscles available so far. For this, one adult male cadaver was studied. Our general approach was to digitize the geometry of each fascicle of the muscles of back proper (Erector spinae) – the Spinalis thoracis, Iliocostalis lumborum, Longissimus thoracis and the Multifidus thoracis et lumborum – and of the deep muscles of the abdomen – Psoas minor, Psoas major and Quadratus lumborum – during a layerwise dissection. Architectural parameters such as fascicle angles to the sagittal and the frontal planes as well as fascicle lengths were determined for each fascicle, and are discussed regarding their consequences for the function of the muscle. For example, compared with the other dorsovertebral muscles, the Longissimus thoracis can produce greater shortening distances because of its relatively long fleshy portions, and it can store more elastic energy due to both its relatively long fleshy and tendinous fascicle portions. The Quadratus lumborum was outstanding because of its many architectural subunits defined by distinct attachment sites and fascicle lengths. The presented database will improve biomechanical models of the human trunk by allowing the incorporation of anisotropic muscle properties such as the fascicle direction into finite element models. This information will help to increase our understanding of the functionality of the human back musculature, and may thereby improve future training concepts.

Salamanders have captured the interest of biologists and roboticists for decades because of their ability to locomote in different environments and their resemblance to early representatives of tetrapods. In this article, we review biological and robotic studies on the kinematics (i.e., angular profiles of joints) of salamander locomotion aiming at three main goals: (i) to give a clear view of the kinematics, currently available, for each body part of the salamander while moving in different environments (i.e., terrestrial stepping, aquatic stepping, and swimming), (ii) to examine what is the status of our current knowledge and what remains unclear, and (iii) to discuss how much robotics and modeling have already contributed and will potentially contribute in the future to such studies.

Vocal production in songbirds requires the control of the respiratory system, the syrinx as sound source and the vocal tract as acoustic filter. Vocal tract movements consist of beak, tongue and hyoid movements, which change the volume of the oropharyngeal–esophageal cavity (OEC), glottal movements and tracheal length changes. The respective contributions of each movement to filter properties are not completely understood, but the effects of this filtering are thought to be very important for acoustic communication in birds. One of the most striking movements of the upper vocal tract during vocal behavior in songbirds involves the OEC. This study measured the acoustic effect of OEC adjustments in zebra finches by comparing resonance acoustics between an utterance with OEC expansion (calls) and a similar utterance without OEC expansion (respiratory sounds induced by a bilateral syringeal denervation). X-ray cineradiography confirmed the presence of an OEC motor pattern during song and call production, and a custom-built Hall-effect collar system confirmed that OEC expansion movements were not present during respiratory sounds. The spectral emphasis during zebra finch call production ranging between 2.5 and 5 kHz was not present during respiratory sounds, indicating strongly that it can be attributed to the OEC expansion.

The axial musculoskeletal system represents the plesiomorphic locomotor engine of the vertebrate body, playing a central role in locomotion. In craniates, the evolution of the postcranial skeleton is characterized by two major transformations. First, the axial skeleton became increasingly functionally and morphologically regionalized. Second, the axial-based locomotion plesiomorphic for craniates became progressively appendage-based with the evolution of extremities in tetrapods. These changes, together with the transition to land, caused increased complexity in the planes in which axial movements occur and moments act on the body and were accompanied by profound changes in axial muscle function. To increase our understanding of the evolutionary transformations of the structure and function of the perivertebral musculature, this review integrates recent anatomical and physiological data (e.g., muscle fiber types, activation patterns) with gross-anatomical and kinematic findings for pivotal craniate taxa. This information is mapped onto a phylogenetic hypothesis to infer the putative character set of the last common ancestor of the respective taxa and to conjecture patterns of locomotor and muscular evolution. The increasing anatomical and functional complexity in the muscular arrangement during craniate evolution is associated with changes in fiber angulation and fiber-type distribution, i.e., increasing obliqueness in fiber orientation and segregation of fatigue-resistant fibers in deeper muscle regions. The loss of superficial fatigue-resistant fibers may be related to the profound gross anatomical reorganization of the axial musculature during the tetrapod evolution. The plesiomorphic function of the axial musculature -mobilization- is retained in all craniates. Along with the evolution of limbs and the subsequent transition to land, axial muscles additionally function to globally stabilize the trunk against inertial and extrinsic limb muscle forces as well as gravitational forces. Associated with the evolution of sagittal mobility and a parasagittal limb posture, axial muscles in mammals also stabilize the trunk against sagittal components of extrinsic limb muscle action as well as the inertia of the body's center of mass. Thus, the axial system is central to the static and dynamic control of the body posture in all craniates and, in gnathostomes, additionally provides the foundation for the mechanical work of the appendicular system.

Different locomotor and postural demands are met partly due to the varying properties and proportions of the muscle fibre types within the skeletal muscles. Such data are therefore important in understanding the subtle relationships between morphology, function and behaviour. The triceps surae muscle group is of particular interest when studying our closest living relatives, the non-human great apes, as they lack a significant external Achilles tendon, crucial to running locomotion in humans and other cursorial species. The aim of this study, therefore, was to determine the proportions of type I (slow) and type II (fast) fibres throughout these muscles in chimpanzees and orangutans using immunohistochemistry. The orangutan had a higher proportion of type I fibres in all muscles compared with the chimpanzees, related to their slower, more controlled movements in their arboreal habitat. The higher proportion of type II fibres in the chimpanzees likely reflects a compromise between their need for controlled mobility when arboreal, and greater speed and power when terrestrial. Overall, the proportion of slow fibres was greater in the soleus muscle compared with the gastrocnemius muscles, and there was some evidence of proximal to distal and medial to lateral variations within some muscles. This study has shown that not only do orangutans and chimpanzees have very different muscle fibre populations that reflect their locomotor repertoires, but it also shows how the proportion of fibre types provides an additional mechanism by which the performance of a muscle can be modulated to suit the needs of a species.

SUMMARYThe body axis plays a central role in tetrapod locomotion. It contributes to the work of locomotion, provides the foundation for the production of mechanical work by the limbs, is central to the control of body posture, and integrates limb and trunk actions. The epaxial muscles of mammals have been suggested to mobilize and globally stabilize the trunk, but the timing and the degree to which they serve a particular function likely depend on the gait and the vertebral level. To increase our understanding of their function, we recorded the activity of the m. multifidus lumborum and the m. longissimus thoracis et lumborum at three cranio-caudal levels in dogs while they walked, trotted and galloped. The level of muscle recruitment was significantly higher during trotting than during walking, but was similar during trotting and galloping. During walking, epaxial muscle activity is appropriate to produce lateral bending and resist long-axis torsion of the trunk and forces produced by extrinsic limb muscles. During trotting, they also stabilize the trunk in the sagittal plane against the inertia of the center of mass. Muscle recruitment during galloping is consistent with the production of sagittal extension. The sequential activation along the trunk during walking and galloping is in accord with the previously observed traveling waves of lateral and sagittal bending, respectively, while synchronized activity during trotting is consistent with a standing wave of trunk bending. Thus, the cranio-caudal recruitment patterns observed in dogs resemble plesiomorphic motor patterns of tetrapods. In contrast to other tetrapods, mammals display bilateral activity during symmetrical gaits that provides increased sagittal stability and is related to the evolution of a parasagittal limb posture and greater sagittal mobility.

Many physiological parameters scale with body size. Regarding limb muscles, it has been shown that the demands for relatively faster muscles, less postural work, and greater heat production in small mammals are met by lower proportions of Type I and conversely higher proportions of Type II fibers. To investigate possible adaptations of the perivertebral musculature, we investigated the proportion, spatial distribution, and cross-sectional area (csa) of the different muscle fiber types in the laboratory and harvest mouse. Serial cross sections from the posterior thoracic to the lumbo-sacral region were prepared and Type I, IIA, and IIB fibers identified using enzymehistochemistry. The general distribution of Type I and IIB fibers, as well as the more or less equal distribution of IIA fibers, resembles the pattern found in other mammals. However, the overall proportion of Type I fibers was very low in the laboratory mouse and particularly low in the harvest mouse. Muscular adaptations to a small body size were met primarily by increased Type IIA fiber proportions. Thereby, not all muscles or muscle regions similarly reflected the expected scaling effects. However, our results clearly show that body size is a critical factor when fiber-type proportions are compared among different sized mammals.

SUMMARY Although humans appear to be specialized for endurance running, the plantigrade posture of our feet, in which the heel contacts the substrate at the beginning of a step, seems incompatible with economical running. In this study, we tested the hypothesis that plantigrade foot posture reduces the energetic cost of transport (COT) during walking in humans. When human subjects walked with their heels slightly elevated in a ‘low-digitigrade’ posture, COT increased by 53% above that of normal plantigrade walking. By contrast, there was no difference in COT when subjects ran with digitigrade versus plantigrade foot posture. Stride frequency increased and stride length decreased when subjects switched to digitigrade walking; however, this change did not influence the COT. Additionally, we found that possible reductions in postural stability appear not to have caused the elevated cost of digitigrade walking. Digitigrade walking, however, did (1) increase the external mechanical work performed by the limbs; (2) reduce the pendular exchange of kinetic and potential energy of the center of mass; (3) increase the average ground reaction force moment at the ankle joint; and (4) increase the recruitment of major extensor muscles of the ankle, knee, hip and back. These observations suggest that plantigrade foot posture improves the economy of walking. Relative to other mammals, humans are economical walkers, but not economical runners. Given the great distances hunter-gatherers travel, it is not surprising that humans retained a foot posture, inherited from our more arboreal great ape ancestors, that facilitates economical walking.

This work deals with the development and implementation of a new fatigue model for simulating fatigue effects in skeletal muscles. Basic idea of this modelling strategy is an approach that divides the fibres of a muscle into three groups: fibres in the active state, those that are already fatigued and fibres in the resting state. All fibres are able to switch between the different groups by defining adequate rates. In this way a continuous transfer of fibres between those three states has been described. Rooted on an incompressible, hyperelastic constitutive law with transversely isotropic characteristics the fatigue model has been implemented in the framework of the finite element method. Numerical examples are given in order to illustrate the ability of this model. Further, we validate the model by fatigue experiments of the rat soleus muscle. In doing so, it proves that the model is able to predict physiological observations and mechanical test results.

SUMMARY The activity of seven trunk muscles was recorded at two sites along the trunk in adult spotted salamander, Ambystoma maculatum, during swimming and during trotting in water and on land. Several muscles showed patterns of activation that are consistent with the muscles producing a traveling wave of lateral bending during swimming and a standing wave of bending during aquatic and terrestrial trotting: the dorsalis trunci,subvertebralis lateralis and medialis, rectus lateralis and obliquus internus. The interspinalis showed a divergent pattern and was active out of phase with the other muscles suggesting that it functions in vertebral stabilization rather than lateral bending. The obliquus internus and rectus abdominis showed bilateral activity indicating that they counteract sagittal extension of the trunk that is produced when the large dorsal muscles are active to produce lateral bending. Of the muscles examined, only the obliquus internus showed a clear shift in function from lateral bending during swimming to resistance of long-axis torsion during trotting. During terrestrial trotting, muscle recruitment was greater in several muscles than during aquatic trotting,despite similar temporal patterns of muscle activation, suggesting that the trunk is stiffened during terrestrial locomotion against greater gravitational forces whereas the basic functions of the trunk muscles in trotting are conserved across environments.

SUMMARY In mammals, the epaxial muscles are believed to stabilize the trunk during walking and trotting because the timing of their activity is not appropriate to produce bending of the trunk. To test whether this is indeed the case, we recorded the activity of the m. multifidus lumborum and the m. longissimus thoracis et lumborum at three different sites along the trunk (T13, L3, L6) as we manipulated the moments acting on the trunk and the pelvis in dogs trotting on a treadmill. Confirming results of previous studies, both muscles exhibited a biphasic and bilateral activity. The higher burst was associated with the second half of ipsilateral hindlimb stance phase, the smaller burst occurred during the second half of ipsilateral hindlimb swing phase. The asymmetry was noticeably larger in the m. longissimus thoracis et lumborum than in the m. multifidus lumborum. Although our manipulations of the inertia of the trunk produced results that are consistent with previous studies indicating that the epaxial muscles stabilize the trunk against accelerations in the sagittal plane, the responses of the epaxial muscles to manipulations of trunk inertia were small compared with their responses when moments produced by the extrinsic muscles of the hindlimb were manipulated. Our results indicate that the multifidus and longissimus muscles primarily stabilize the pelvis against(1) vertical components of hindlimb retractor muscles and (2) horizontal components of the hindlimb protractor and retractor muscles. Consistent with this, stronger effects of the manipulations were observed in the posterior sampling sites.

Many salamanders locomote in aquatic and terrestrial environments. During swimming, body propulsion is solely produced by the axial musculature generating lateral undulations of the trunk and tail. During terrestrial locomotion, the trunk is oscillated laterally in a standing wave, and body propulsion is achieved by concerted trunk and limb muscle action. The goal of this study was to increase our knowledge of the functional morphology of the tetrapod trunk. We investigated the muscle-fiber-type distribution and the anatomical cross-sectional area of all perivertebral muscles in Ambystoma tigrinum and A. maculatum. Muscle-fiber-type composition was determined in serial cross-sections based on m-ATPase activity. Five different body segments were investigated to test for cranio-caudal changes along the trunk. The overall fiber-type distribution was very similar between the species, but A. tigrinum had relatively larger muscles than A. maculatum, which may be related to its digging behavior. None of the perivertebral muscles possessed a homogeneous fiber-type composition. The M. interspinalis showed a distinct layered organization and may function to ensure the integrity of the spine (local stabilization). The M. dorsalis trunci exhibited the plesiomorphic pattern for notochordates in having a distinct superficial layer of red and intermediate fibers, which covered the central white fibers; therefore, it is suggested to function as a mobilizer and a stabilizer of the trunk, but, may also be involved in modulating body stiffness. Similarly, the M. subvertebralis showed clear regionalizations, implying functional subunits that can stabilize and mobilize the trunk as well as modulate of body stiffness. Cranio-caudally, neither the fiber-type composition nor the a-csa changed dramatically, possibly reflecting the need to perform well in both aquatic and terrestrial habitats. J. Morphol., 2010. © 2009 Wiley-Liss, Inc.

SUMMARYMammalian locomotion is characterized by the use of asymmetrical gaits associated with extensive flexions and extensions of the body axis. Although the impact of sagittal spine movements on locomotion is well known, little information is available on the kinematics of spinal motion. Intervertebral joint movements were studied in two metatherian and three eutherian species during the gallop and halfbound using high-speed cineradiography. Fast-Fourier transformation was used to filter out high frequency digitizing errors and keep the lower frequency sinusoid oscillations that characterize the intervertebral angular movements. Independent of their regional classification as thoracic or lumbar vertebrae, 7±1 presacral intervertebral joints were involved in sagittal bending movements. In only one species, no more than five intervertebral joints contributed to the resulting `pelvic movement'. In general, the trunk region involved in sagittal bending during locomotion did not correspond to the traditional subdivisions of the vertebral column (e.g. as thoracic and lumbar or pre- and postdiaphragmatic region). Therefore, these classifications do not predict the regions involved in spinal oscillations during locomotion. Independent of the gait, maximum flexion of the spine was observed in the interval between the last third of the swing phase and touch-down. This results in a retraction of the pelvis and hindlimbs before touch-down and, we hypothesize, enhances the stability of the system. Maximum extension occurred during the first third of the swing phase (i.e. after lift-off) in all species. In general, the observed timing of dorsoventral oscillations of the spine are in accordance with that observed in other mammals and with activity data of respiratory and epaxial back muscles. Although no strict craniocaudal pattern was observable, the more cranial intervertebral joints tend to flex and extend earlier than the more caudal ones. This is in accordance with the organization and the activation of the paravertebral musculature in mammals. The amplitude of intervertebral joint movements increased caudally, reaching its highest values in the presacral joint. The more intense sagittal bending movements in the caudal intervertebral joints are reflected by the muscle fiber type composition of the back muscles involved. Despite the highly similar amplitude of `pelvic motion', touch-down and lift-off positions of the pelvis were clearly different between the species with a long, external tail and those with no external tail.

We investigated the functional corollaries of a relatively long trunk with regard to trunk use during overground and underground locomotion and with regard to fibre-type distribution within the paravertebral musculature using the example of the domestic ferret. Fibre-type distribution was determined using enzyme histochemistry on serial cross-sections through the complete musculo-skeletal apparatus. Back posture and back movements were analysed using cineradiography. During overground locomotion, the back is bent into an arch, resulting in a back length comparable to normally proportioned small mammals. During underground locomotion, the back is held straight, resulting in greater rotational inertia and higher stabilisation requirements. This is reflected in the fibre-type distribution pattern, which differs clearly from that of all other mammals investigated so far. Instead of being separated into superficial, glycolytic and deep, oxidative parts, all the epaxial and the iliopsoas muscles consisted of 20-30% oxidative, 20-30% oxidative-glycolytic and 40-60% glycolytic fibres, with no or only minor differences between superficial and profound muscles or muscle regions. Only the quadratus lumborum muscle showed a fibre-type distribution comparable to other mammals, reflecting its primary function as an accessory muscle of respiration. We suggest that the observed pattern reflects the adaptation of the back muscles to the functional demands of a long trunk and the increased need to stabilise it during overground and especially underground locomotion.

Muscle fiber type composition of intrinsic shoulder muscles was examined in tree shrews, cotton-top tamarins, and squirrel monkeys with respect to their shoulder kinematics and forelimb loading during locomotion. Enzyme- and immunohistochemical techniques were applied to differentiate muscle fiber types on serial cross-sections of the shoulder. In the majority of the shoulder muscles, the proportions of fatigue resistant slow-twitch fibers (SO) and fatigable fast-twitch fibers (FG) were inversely related to each other, whereas the percentage of intermediate FOG-fibers varied independently. A segregation of fatigue resistant SO-fibers into deep muscle regions is indicative of differential activation of histochemically distinct muscle regions in which deep regions stabilize the joint against gravitational loading. In all three species, this antigravity function was demonstrated for both the supraspinatus and the cranial subscapularis muscle, which prevent passive joint flexion during the support phase of the limb. The infraspinatus muscle showed a high content of SO-fibers in the primate species but not in the tree shrew, which demonstrates the "new" role of the infraspinatus muscle in joint stabilization related to the higher degree of humeral protraction in primates. In the tree shrew and the cotton-top tamarin, a greater proportion of the body weight is carried on the forelimb, but the squirrel monkey exhibits a weight shift to the hind limbs. The lower amount of forelimb loading is reflected by an overall lower proportion of fatigue resistant muscle fibers in the shoulder muscles of the squirrel monkey. Several muscles such as the deltoid no longer function as joint stabilizers and allow the humerus to move beyond the scapular plane. These differences among species demonstrate the high plasticity of the internal muscle architecture and physiology which is suggested to be the underlying reason for different muscle activity patterns in homologous muscles. Implications for the evolution of new locomotor modes in primates are discussed.

SUMMARYComparative studies of locomotion indicate that limb design and performance are very similar in adult mammals of small to medium size. The present study was undertaken to test whether basic therian limb pattern is present during postnatal development. Kinematic data were collected from juveniles of two eutherian species in a cross-sectional study, using cinevideography. The tree shrew Tupaia glis and the cui Galea musteloides were selected because of their different reproductive strategies, which could result in differences in the development of locomotor abilities. The aims of this study were to describe the process by which young animals develop the adult pattern of locomotion and the extent to which this process varies in two species with very different postnatal ontogenies.Despite their different life histories, the development of kinematic parameters in the altricial tree shrew and the precocial cui are surprisingly similar. General limb design, performance, and timing of segment and joint movements in the young animals were similar to adults in both species, even from the first steps. Touch-down of the forelimb occurred at the position below the eye in all individuals and limb position was highly standardized at touch-down; no major changes in segment and joint angles were observed. Significant changes occurred at lift-off. With increasing body mass, limb segments rotated more caudally, which resulted in larger limb excursions and relatively longer steps. Developmental changes in locomotor abilities were similar in both species; only the time necessary to reach the adult performance was different. Despite the widely assumed maturity of locomotor abilities in precocial young, the first steps of the cui juveniles were not similar to the movements of adults. The adult locomotor pattern was reached within the first postnatal week in the cui and by the time they leave the nest in the tree shrew (39 days after birth; individual P39).These results suggest that during the evolution of precocial development only processes independent of exercise or gravity can be shifted into the intrauterine period. However, development of locomotor ability dependents on exercise, and adjustments and training occur during growth. Therefore, only the time necessary to reach maturity was clearly shortened in the precocial juvenile relative to the ancestral altricial condition.

During the evolution of therian mammals, the two-segmented, sprawled tetrapod limbs were transformed into three-segmented limbs in parasagittal zig-zag configuration (three-segment limb hypothesis). As a consequence, the functional correspondence of limb segments has changed (now: scapula to thigh, upper arm to shank, fore arm plus hand to foot). Therefore, the scapula was taken into account in the current study of the postnatal growth of the postcranial skeleton in two small mammalian species (Tupaia glis, Galea musteloides). Comparisons were made between the functionally equivalent elements and not in the traditional way between serially homologous segments. This study presents a test of the three-segment limb hypothesis which predicts a greater ontogenetic congruence in the functionally equivalent elements in fore and hind limbs than in the serially homologous elements. A growth sequence, with decreasing regression coefficients from proximal to distal, was observed in both species under study. This proximo-distal growth sequence is assumed to be ancestral in the ontogeny of eutherian mammals. Different reproductive modes have evolved within eutherian mammals. To test the influence of different life histories on ontogenetic scaling during postnatal growth, one species with altricial juveniles (Tupaia glis) assumed to be the ancestral mode of development for eutherians and one species with derived, precocial young (Galea musteloides) were selected. The growth series covered postnatal development from the first successive steps with a lifted belly to the adult locomotory pattern; thus, functionally equivalent developmental stages were compared. The higher number of allometrically positive or isometrically growing segments in the altricial mammalian species was interpreted as a remnant of the fast growth period in the nest without great locomotor demands, and the clearly negative allometry in nearly all segments in the precocial young was interpreted as a response to the demand on early locomotor activity. Different life histories seem to have a strong influence on postnatal ontogenetic scaling; the effects of the developmental differences are still observable when comparing adults of the two species.

Considerations about back pain, its aetiology, pathogenesis and therapy often argue that low back pain is the "price" that humanity has to pay for the upright body posture and the bipedal mode of locomotion. In fact, there are only few species that have evolved an obligate bipedal locomotion (e.g. kangaroos). Surprisingly, there are only minor morphological adaptations in humans clearly connected to the upright body posture (e.g. the habitual lumbar lordosis). The overall organization of the body axis has been evolved in quadrupedal animals and was more or less unchanged suitable for the human bipedal mode of locomotion. Up to now, the assumed uniqueness of human's trunk does not explain the frequency of back problems. Because of minor macroscopic differences between humans and other mammals, and even primates, we started to take a closer look at the paravertebral musculature. A three-dimensional investigation of muscle's fibre type distribution was undertaken on laboratory rats. Serial sections from the caudal thoracic and lumbar regions of the back were analysed, and the fibre type distribution pattern in all paravertebral muscles was described. Comparisons to other species imply more general characters of the fibre type distribution in mammals. Established concepts of human back muscle function were exposed to be valid for quadruped mammals as well. Muscle properties predicted by a biomechanical model based on human's anatomy (Wagner et al., this issue) were confirmed by results of the current study on a small mammal. Therefore, we propose only minor differences from the observed pattern in human back muscles.

SUMMARYIn three species of small therian mammals (Scandentia: Tupaia glis, Rodentia: Galea musteloides and Lagomorpha: Ochotona rufescens) the net joint forces and torques acting during stance phase in the four kinematically relevant joints of the forelimbs (scapular pivot,shoulder joint, elbow joint, wrist joint) and the hindlimbs (hip joint, knee joint, ankle joint, intratarsal joint) were determined by inverse dynamic analysis.Kinematics were measured by cineradiography (150 frames s-1). Synchronously ground reaction forces were acquired by forceplates. Morphometry of the extremities was performed by a scanning method using structured illumination.The vector sum of ground reaction forces and weight accounts for most of the joint force vector. Inertial effects can be neglected since errors of net joint forces amount at most to 10 %. The general time course of joint torques is comparable for all species in all joints of the forelimb and in the ankle joint. Torques in the intratarsal joints differ between tailed and tail-less species. The torque patterns in the knee and hip joint are unique to each species.For the first time torque patterns are described completely for the forelimb including the scapula as the dominant propulsive segment. The results are compared with the few torque data available for various joints of cats(Felis catus), dogs (Canis lupus f. familiaris),goats (Capra sp.) and horses (Equus przewalskii f. caballus).

The complete list of authors is as follows: Markus Bol (Institute of Solid Mechanics, Department of Mechanical Engineering, Technische Universitat Carolo-Wilhelmina) (as corresponding author), Nadja Schilling (Institute of SystematicZoology andEvolutionaryBiology, Friedrich-Schiller-University Jena) and Heiko Stark (Institute of Systematic Zoology and Evolutionary Biology, Friedrich-Schiller-University Jena).