Hindlimb Joints Research Articles

Morphology of the pelvis and hind limb of the red panda (Ailurus fulgens) evidenced by gross osteology, radiography and computed tomography.

The red panda (Ailurus fulgens) is a quadrupedal arboreal animal primarily distributed in the Himalayas and southern China. It is a species commonly kept in zoological collections. This study was carried out to describe the morphology of the pelvis and hind limb of the red panda evidenced by gross osteology, radiography and computed tomography as a reference for clinical use and identification of skeletons. Radiography of the pelvis and right hind limb was performed in nine and seven animals, respectively. Radiographic findings were correlated with bone specimens from three adult animals. Computed tomography of the torso and hind limb was performed in one animal. The pelvic bone had a wide ventromedial surface of the ilium. The trochlea of the femur was wide and shallow. The patella was similar to that seen in feline species. The medial fabella was not seen radiographically in any animal. The cochlea grooves of the tibia were shallow with a poorly defined intermediate ridge. The trochlea of the talus was shallow and presented with an almost flattened medial ridge. The tarsal sesamoid bone was always present. The lateral process of the base of the fifth metatarsal (MT) bone was directed laterally. The MT bones were widely spaced. The morphology of the pelvis and hind limb of the red panda indicated flexibility of the pelvis and hind limb joints as an adaptation to an arboreal quadrupedal lifestyle.

Goniometric evaluation of both forelimbs and hind limbs in two species of Neotropical monkeys.

The aim of this study was to evaluate the goniometric measurements of the forelimb and hind limb joints in two species of Neotropical primates maintained in captivity. Eighteen intact monkeys organized into two groups were studied: Group 1-9 brown howlers (Alouatta fusca), and Group 2-9 tufted capuchins (Sapajus apella). Significant differences were observed in the maximum flexion of the shoulder, elbow, carpus, stifle, and tarsus (G1>G2); maximum extension and abduction of the shoulder (G1<G2); maximum extension (G1>G2) and adduction (G1<G2) of the carpus; and maximum extension, abduction and adduction of the hip (G1>G2). The ROM was significantly different in all joints: shoulder (G1<G2), elbow (G1<G2), carpus (G1>G2), hip (G1>G2), stifle (G1<G2), and tarsus (G1<G2). A. fusca and S. apella maintained in captivity have significant differences in the goniometric measurements of both forelimb and hind limb joints, primarily in maximum flexion and ROM.

Foot strike patterns and hind limb joint angles during running in Hadza hunter-gatherers

BackgroundInvestigations of running gait among barefoot and populations have revealed a diversity of foot strike behaviors, with some preferentially employing a rearfoot strike (RFS) as the foot touches down while others employ a midfoot strike (MFS) or forefoot strike (FFS). Here, we report foot strike behavior and joint angles among traditional Hadza hunter-gatherers living in Northern Tanzania. MethodsHadza adults (n = 26) and juveniles (n = 14) ran at a range of speeds (adults: mean 3.4 ± 0.7 m/s, juveniles: mean 3.2 ± 0.5 m/s) over an outdoor trackway while being recorded via high-speed digital video. Foot strike type (RFS, MFS, or FFS) and hind limb segment angles at foot strike were recorded. ResultsHadza men preferentially employed MFS (86.7% of men), while Hadza women and juveniles preferentially employed RFS (90.9% and 85.7% of women and juveniles, respectively). No FFS was recorded. Speed, the presence of footwear (sandals vs. barefoot), and trial duration had no effect on foot strike type. ConclusionUnlike other habitually barefoot populations which prefer FFS while running, Hadza men preferred MFS, and Hadza women and juveniles preferred RFS. Sex and age differences in foot strike behavior among Hadza adults may reflect differences in running experience, with men learning to prefer MFS as they accumulate more running experience.

Biomechanical and functional variation in rat sciatic nerve following cuff electrode implantation.

BackgroundNerve cuff electrodes are commonly and successfully used for stimulating peripheral nerves. On the other hand, they occasionally induce functional and morphological changes following chronic implantation, for reasons not always clear. We hypothesize that restriction of nerve mobility due to cuff implantation may alter nerve conduction.MethodsWe quantified acute changes in nerve-muscle electrophysiology, using electromyography, and nerve kinematics in anesthetized Sprague Dawley rat sciatic nerves during controlled hindlimb joint movement. We compared electrophysiological and biomechanical response in uncuffed nerves and those secured within a cuff electrode using analysis of variance (ANOVA) and regression analysis.ResultsTethering resulting from cuff implantation resulted in altered nerve strain and a complex biomechanical environment during joint movement. Coincident with biomechanical changes, electromyography revealed significantly increased variability in the response of conduction latency and amplitude in cuffed, but not free, nerves following joint movement.ConclusionOur findings emphasize the importance of the mechanical interface between peripheral nerves and their devices on neurophysiological performance. This work has implications for nerve device design, implantation, and prediction of long-term efficacy.

Analysis on bilateral hindlimb mapping in motor cortex of the rat by an intracortical microstimulation method.

Intracortical microstimulation (ICMS) is a technique that was developed to derive movement representation of the motor cortex. Although rats are now commonly used in motor mapping studies, the precise characteristics of rat motor map, including symmetry and consistency across animals, and the possibility of repeated stimulation have not yet been established. We performed bilateral hindlimb mapping of motor cortex in six Sprague-Dawley rats using ICMS. ICMS was applied to the left and the right cerebral hemisphere at 0.3 mm intervals vertically and horizontally from the bregma, and any movement of the hindlimbs was noted. The majority (80%± 11%) of responses were not restricted to a single joint, which occurred simultaneously at two or three hindlimb joints. The size and shape of hindlimb motor cortex was variable among rats, but existed on the convex side of the cerebral hemisphere in all rats. The results did not show symmetry according to specific joints in each rats. Conclusively, the hindlimb representation in the rat motor cortex was conveniently mapped using ICMS, but the characteristics and inter-individual variability suggest that precise individual mapping is needed to clarify motor distribution in rats.

Measurements of normal joint angles by goniometry in calves

The aim of this study was to establish normal reference values of the forelimb and hindlimb joint angles in normal Holstein calves. Thirty clinically normal Holstein calves that were free of any detectable musculoskeletal abnormalities were included in the study. A standard transparent plastic goniometer was used to measure maximum flexion, maximum extension, and range-of-motion of the shoulder, elbow, carpal, hip, stifle, and tarsal joints. The goniometric measurements were done on awake calves that were positioned in lateral recumbency. The goniometric values were measured and recorded by two independent investigators. As a result of the study it was concluded that goniometric values obtained from awake calves in lateral recumbency were found to be highly consistent and accurate between investigators (p <0.05). The data of this study acquired objective and useful information on the normal forelimb and hindlimb joint angles in normal Holstein calves. Further studies can be done to predict detailed goniometric values from different diseases and compare them.

Tail autotomy and subsequent regeneration alter the mechanics of locomotion in lizards.

Animals can undergo significant weight change for a variety of reasons. Autotomy, the voluntary shedding of an appendage in response to a predator stimulus, provides an effective model for measuring the effects of rapid weight change on locomotor behavior and the responses to more gradual weight gain, particularly in lizards capable of both autotomizing and regenerating their tail. Although the general effects of autotomy on locomotor performance are commonly explored, we investigated changes in locomotor mechanics associated with tail loss and long-term regeneration for the first time by measuring morphology, 3D kinematics and ground reaction forces (GRFs) in the leopard gecko Eublepharis macularius. Tail autotomy resulted in a 13% anterior shift in the center of mass (CoM), which only partially recovered after full regeneration of the tail. Although no changes in body or forelimb kinematics were evident, decreases in hindlimb joint angles signify a more sprawled posture following autotomy. Changes in hindlimb GRFs resulted in an increase in weight-specific propulsive force, without a corresponding change in locomotor speed. Hindlimb kinematics and GRFs following autotomy recovered to pre-autotomy values as the tail regenerated. These results suggest an active locomotor response to tail loss that demonstrates the causal relationships between variations in morphology, kinematics and force.

Effect of fence height on joint angles of agility dogs

The Kennel Club (KC) and United Kingdom Agility (UKA) govern major dog agility competitions in the UK. Dogs are categorised into different jump heights depending on their height at the withers, with fence heights ranging from 300 to 650mm for both organisations. Dogs fall into one of three height categories when competing under KC rules and one of four height categories under UKA rules. The aim of this study was to investigate the influence of an additional height category for agility dogs measuring over 430mm at the withers. Jump heights were selected that related to the percentage of body height that dogs of 430mm (7% lower) and 431mm (51% higher) height at the withers would be encouraged to jump under UKA regulations without the addition of their fourth (‘standard height’) category. Joint angles were determined from anatomical markers placed on the forelimb and hind limb joints, and at six points along the vertebral column. As fence height increased, flexion of the scapulohumeral joint increased significantly for both the take-off and bascule (arc) phases of the jump. The increase in flexion as a consequence of the increase in fence height is likely to result in intensified stretching of the biceps brachii and supraspinatus muscles. In addition, increasing fence high resulted in an increase in the sacroiliac joint angle during take-off.

SAT0074 Selectively antagonizing the EP4 prostanoid receptor significantly ameliorates pathological features in a rat model for inflammatory arthritis

BackgroundRecent studies highlight the role of the EP4 prostanoid receptor in promoting autoimmune inflammation via T helper cells, namely Th1 and Th17.ObjectivesAim of the present studies was to test CR6086,...

Modulation of joint moments and work in the goat hindlimb with locomotor speed and surface grade

Goats and other quadrupeds must modulate the work output of their muscles to accommodate the changing mechanical demands associated with locomotion in their natural environments. This study examined which hindlimb joint moments goats use to generate and absorb mechanical energy on level and sloped surfaces over a range of locomotor speeds. Ground reaction forces and the three-dimensional locations of joint markers were recorded as goats walked, trotted and galloped over 0, +15 and -15 deg sloped surfaces. Net joint moments, powers and work were estimated at the goats' hip, knee, ankle and metatarsophalangeal joints throughout the stance phase via inverse dynamics calculations. Differences in locomotor speed on the level, inclined and declined surfaces were characterized and accounted for by fitting regression equations to the joint moment, power and work data plotted versus non-dimensionalized speed. During level locomotion, the net work generated by moments at each of the hindlimb joints was small (less than 0.1 J kg(-1) body mass) and did not vary substantially with gait or locomotor speed. During uphill running, by contrast, mechanical energy was generated at the hip, knee and ankle, and the net work at each of these joints increased dramatically with speed (P<0.05). The greatest increases in positive joint work occurred at the hip and ankle. During downhill running, mechanical energy was decreased in two main ways: goats generated larger knee extension moments in the first half of stance, absorbing energy as the knee flexed, and goats generated smaller ankle extension moments in the second half of stance, delivering less energy. The goats' hip extension moment in mid-stance was also diminished, contributing to the decrease in energy. These analyses offer new insight into quadrupedal locomotion, clarifying how the moments generated by hindlimb muscles modulate mechanical energy at different locomotor speeds and grades, as needed to accommodate the demands of variable terrain.

Qualitative Comparison between Rats and Humans in Quadrupedal and Bipedal Locomotion

Bipedal (Bp) locomotion is one of the most characteristic motor behaviors in human beings. Innate quadrupedal (Qp) four-legged animals also often walk bipedally. The walking posture, however, is significantly different between the two. This suggests that although both have a potential to walk bipedally, however, the human has a body scheme suitable for Bp locomotion, probably its skeletal system. The skeletal system includes the lumbar lordosis, sacral kyphosis, a round pelvis, a large femur neck angle, short feet, and so on. To verify this hypothesis, we compared kinematic and EMG activities between rats and humans during Qp and Bp locomotion on a treadmill belt. The rat is a representative Qp animal, but it is able to acquire Bp walking capability with motor learning. Although the mobile ranges of the hindlimb joint are different during each locomotor pattern between rats and humans, both showed replicable flexion and extension excursion patterns for each joint depending on the locomotor phase. There are many phase-locked EMG bursts between rats and humans during the same walking task and these are observed in the proximal rather than the distal muscles. This suggests that both rats and humans utilize similar neuronal systems for the elaboration of Qp and Bp locomotion. It was interesting that both subjects showed more muscle activities during non-natural locomotor patterns; Qp < Bp for rats and Bp < Qp for humans. This indicates that rat Bp and human Qp walking need more effort and we may be able to find its reason in their skeletal system.

Video-based Gait Analysis for Functional Evaluation of Healing Achilles Tendon in Rats

Video-based walking track systems have been developed for gait analysis in rat models. However, there is no previous study using video-based tracking systems to address the gait parameters to evaluate the recovery of Achilles tendon rupture models. This study conducted a comprehensive gait analysis using a video-based image processing system. Eighteen Sprague-Dawley rats were randomly assigned to one of three interventional conditions: sham surgery, Achilles tendon repair, and Achilles tendon defect. After surgery, all animals were evaluated using a video-based walking track system. The gait parameters and the Achilles functional index (AFI) were further analyzed. The ankle joint angles of the injury side at mid-stance and pre-swing were highly correlated with the AFI. However, lack of sensitivity was found for the AFI. Increased measurement sensitivity of the Achilles tendon healing condition was found in the ankle joint angle of the involved side at the pre-swing and the level of asymmetry of the hindlimb joint position and stance/swing time. The overall sensitivity of the ankle motion analysis was significantly higher than that of AFI. We conclude that the ankle motion analysis is a reliable, reproducible, and sensitive tool for Achilles tendon analysis in rats.

Improving Regions of Deviation Gait Symmetry Analysis With Pointwise t Tests

The regions of deviation method has been proposed as a technique for identifying regions of the gait cycle where joint motion deviates from normal (Shorter et al., 2008). The original statistical analysis distinguished only peak values during stance and swing. In the current article, we extend the approach by examining deviations from normal throughout the entire gait cycle using pointwise t tests. These methods were demonstrated on hind-limb joint angles of 21 Labrador Retrievers without and with cranial cruciate ligament disease. Results were compared with peak difference analysis previously performed on these subjects. All points in the gait cycle where symmetry deviations were significantly affected by cranial cruciate ligament disease (via pointwise t tests) were defined as regions of deviation from symmetry. Discriminant function analysis was used to consider single subjects and validate that these regions were truly areas of difference between groups. Regions of deviation encompassed previously determined significant peak differences, while extending analysis to additional areas of asymmetry. Discriminant function analysis suggested that the region of deviation method is a viable approach for distinguishing motion pattern differences. This enhanced method may help researchers better understand the mechanisms behind lameness and compensation.

Stance-phase force on the opposite limb dictates swing-phase afferent presynaptic inhibition during locomotion

Presynaptic inhibition is a powerful mechanism for selectively and dynamically gating sensory inputs entering the spinal cord. We investigated how hindlimb mechanics influence presynaptic inhibition during locomotion using pioneering approaches in an in vitro spinal cord-hindlimb preparation. We recorded lumbar dorsal root potentials to measure primary afferent depolarization-mediated presynaptic inhibition and compared their dependence on hindlimb endpoint forces, motor output, and joint kinematics. We found that stance-phase force on the opposite limb, particularly at toe contact, strongly influenced the magnitude and timing of afferent presynaptic inhibition in the swinging limb. Presynaptic inhibition increased in proportion to opposite limb force, as well as locomotor frequency. This form of presynaptic inhibition binds the sensorimotor states of the two limbs, adjusting sensory inflow to the swing limb based on forces generated by the stance limb. Functionally, it may serve to adjust swing-phase sensory transmission based on locomotor task, speed, and step-to-step environmental perturbations.

Acetyl-l-carnitine treatment following spinal cord injury improves mitochondrial function correlated with remarkable tissue sparing and functional recovery

We have recently documented that treatment with the alternative biofuel, acetyl-l-carnitine (ALC, 300 mg/kg), as late as 1 h after T10 contusion spinal cord injury (SCI), significantly maintained mitochondrial function 24 h after injury. Here we report that after more severe contusion SCI centered on the L1/L2 segments that are postulated to contain lamina X neurons critical for locomotion (the “central pattern generator”), ALC treatment resulted in significant improvements in acute mitochondrial bioenergetics and long-term hind limb function. Although control-injured rats were only able to achieve slight movements of hind limb joints, ALC-treated animals produced consistent weight-supported plantar steps 1 month after injury. Such landmark behavioral improvements were significantly correlated with increased tissue sparing of both gray and white matter proximal to the injury, as well as preservation of choline acetyltransferase (ChAT)-positive neurons in lamina X rostral to the injury site. These findings signify that functional improvements with ALC treatment are mediated, in part, by preserved locomotor circuitry rostral to upper lumbar contusion SCI. Based on beneficial effects of ALC on mitochondrial bioenergetics after injury, our collective evidence demonstrate that preventing mitochondrial dysfunction acutely “promotes” neuroprotection that may be associated with the milestone recovery of plantar, weight-supported stepping.

HOW LIZARDS TAKE OFF FROM A STANDING START

If you've ever tried to catch a lizard you'll know they move like greased lightening. More like the Usain Bolt of the animal world than Haile Gebrselassie, they swiftly dodge predators and pounce on prey. Eric McElroy, from the College of Charleston, USA, explains that he is intrigued by how muscles power movement and says, ‘Most of the thoughts on how lizards move are based on studies of steady speed movement, but what we realised was that burst activity is another aspect of the animal's behaviour. The first step to understanding what their muscles are doing during that burst is to understand the kinematics of them moving.’ Teaming up with undergraduate Kristen Archambeau, McElroy began filming lizards in 3-D as they took off from a standing start to begin to understand how they power fast take-offs (p. 442).Having built a 3 m long racetrack, McElroy was ready to start filming Sceloporous woodi lizards when Lance McBrayer delivered 10 of the animals from Florida. Painting white markers on the lizards' hindlimb joints, McElroy carefully covered each animal with a bag to transfer it to the racetrack before gently removing the bag and spooking the animal with a loud clap. Filming the first three strides of each frantic dash at 300 frames s–1 from the side and above, McElroy and Archambeau then painstakingly reconstructed the three-dimensional course of each limb joint to find out how the lizards sprang into action.Analysing the animals' stride patterns, McElroy and McBrayer realised that instead of pushing off with one foot, the lizards started about half of their escape dashes by pushing off with two. ‘Kinematically that first step looks like a jump’, says McElroy. And as they analysed the lizards' movements further, they realised that each stride was very different. ‘One of the key differences is that the hip, the knee and the ankle seem to really change what they are doing across all three strides. For example, the knee and ankle sweep through huge angles during the first stride and then by the third stride they seem to stiffen and not sweep through very large angles’, McElroy recalls.The animals' accelerations also varied dramatically from stride to stride, peaking during the first stride and falling to almost zero by the third stride. ‘The first stride is pure acceleration’, says McElroy, and adds that the animals are likely approaching their top speed by the time they hit the fourth and fifth strides and they generate the most power during the first and second strides.However, when the team searched for correlations between particular aspects of the lizards' movements and their acceleration patterns, they found few. ‘We were surprised that the kinematics that we recorded were in general poor predictors of acceleration performance. Our working hypothesis entering this study was that the angular kinematics at the joint should predict acceleration because it is the angular kinematics that presumably reflect what a muscle is doing, and yet the joint kinematics that we recorded had relatively poor predictive power.’Having measured the fleeing animals' movements as they powered off from a standing start, McElroy is keen to build a computational model of the lizards and their movements. Ultimately, he hopes to use this model to calculate the forces pulling the joints and to understand how muscles in animals with radically different musculature function to move their limbs in similar ways.

Goniometric measurements of the forelimb and hindlimb joints in sheep

The aim of this study was to evaluate angle-of-motion values for the forelimb and hindlimb in clinically healthy adult Santa Ines sheep by means of a standard goniometer. Twenty female Santa Ines sheep, ranging in age between three- to six-years-old, and weighing 32-45 kg (mean ± standard deviation [SD]: 30.4 ± 3.7) were used. A standard transparent plastic goniometer was used to measure passive maximum flexion, maximum extension, and range-of-motion (ROM) of the shoulder, elbow, carpal, hip, stifle, and tarsal joints in the right and left limbs. The goniometric measurements were done with the sheep awake and in a standing position. The measurements were made in triplicate by two independent investigators. In all evaluated joints, there was no significant difference either between the means of the two sides or between measurements performed by the two investigators. The mean ± SD values of the measurements (degrees) were as follows: 20 ± 1 (flexion), 170 ± 2 (extension), and 150 ± 2 (ROM) for the carpal joint; 34 ± 4 (flexion), 145 ± 6 (extension), and 110 ± 4 (ROM) for the elbow joint; 88 ± 2 (flexion), 144 ± 6 (extension), and 56 ± 5 (ROM) for shoulder joint; 35 ± 4 (flexion), 163 ± 3 (extension), and 129 ± 4 (ROM) for tarsal joint; 46 ± 4 (flexion), 146 ± 6 (extension), and 100 ± 4 (ROM) for the stifle joint; 54 ± 3 (flexion), 143 ± 7 (extension), and 89 ± 5 (ROM) for the hip joint. The data obtained provide useful and objective information on the joints. More studies are necessary using other sheep breeds.

The sensitivity of two-dimensional hindlimb joint kinematics analysis in assessing functional recovery in rats after sciatic nerve crush

Walking analysis in the rat is increasingly used to assess functional recovery after peripheral nerve injury. Here we assess the sensitivity and specificity of hindlimb joint kinematics measures during the rat gait early after sciatic nerve crush injury (DEN), after twelve weeks of recovery (REINN) and in sham-operated controls (Sham) using discriminant analysis. The analysis addressed gait spatiotemporal variables and hip, knee and ankle angle and angular velocity measures during the entire walking cycle. In DEN animals, changes affected all studied joints plus spatiotemporal parameters of gait. Both the spatiotemporal and ankle kinematics parameters recovered to normality within twelve weeks. At this time point, some hip and knee kinematics values were still abnormal when compared to sham controls. Discriminant models based on hip, knee and ankle kinematics displayed maximal sensitivity to identify DEN animals. However, the discriminant models based on spatiotemporal and ankle kinematics data showed a poor performance when assigning animals to the REINN and Sham groups. Models using hip and knee kinematics during walking showed the best sensitivity to recognize the reinnervated animals. The model construed on the basis of hip joint kinematics was the one combining highest sensitivity with robustness and high specificity. It is concluded that ankle joint kinematics fails in detecting minor functional deficits after long term recovery from sciatic nerve crush and extending the kinematic analysis during walking to the hip and knee joints improves the sensitivity of this functional test.

Submaximal leaping in the grey mouse lemur

In arboreal animals such as the grey mouse lemur ( Microcebus murinus Miller, 1777), leaping is the most frequent strategy for predator avoidance. The aim of this study was to characterise the locomotor adaptation in response to the structural constraint of the habitat (i.e., position of the landing substrate). Thus, we characterised the push-off phase by inducing the lemurs to leap up to a range of heights from horizontal to their own individual highest performance. Using uniplanar high-frequency cineradiographs collected in a sagittal plane, the relative contributions of the centre of mass (CoM) velocity vector magnitude and orientation to leaping performance were evaluated. The kinematics of the push-off phase showed that for low landing heights, leaping performance was essentially due to hip and knee extensions. Higher leaps seemed to be related to an increase in ankle contribution. At all leaping heights, the proximal-to-distal sequence of the hind limb joints controlled the orientation and magnitude of the M. murinus CoM velocity vector while pushing off. Finally, the analysis of the velocity vector at the onset of take-off suggested that the optimal solution for predator avoidance was to leap for horizontal distance and not for vertical distance.

Toe function and dynamic pressure distribution in ostrich locomotion

The ostrich is highly specialized in terrestrial locomotion and is the only extant bird that is both didactyl and exhibits a permanently elevated metatarsophalangeal joint. This extreme degree of digitigrady provides an excellent opportunity for the study of phalangeal adaptation towards fast, sustained bipedal locomotion. Data were gathered in a semi-natural setting with hand-raised, cooperative specimens. Dynamic pressure distribution, centre of pressure (CoP) trajectory and the positional inter-relationship of the toes during stance phase were investigated using pedobarography. Walking and running trials shared a J-shaped CoP trajectory with greater localization of CoP origin as speed increased. Slight variations of 4th toe position in walking affect CoP origin and modulation of 4th toe pressure on the substrate allows correction of balance, primarily at the beginning of stance phase at lower speeds. Load distribution patterns differed significantly between slow and fast trials. In walking, the 3rd and particularly the 4th toe exhibited notable variation in load distribution with minor claw participation only at push-off. Running trials yielded a distinctly triangular load distribution pattern defined by the 4th toe tip, the proximal part of the 3rd toe and the claw tip, with the sharp point of the claw providing an essential traction element at push-off. Consistency of CoP trajectory and load distribution at higher speeds arises from dynamic stability effects and may also reflect stringent limitations to degrees of freedom in hindlimb joint articulation that contribute to locomotor efficiency. This novel research could aid in the reconstruction of theropod locomotor modes and offers a systemic approach for future avian pedobarographic investigations.