Biomedical subjects

Peter Aerts

Publications and source records attributed to Peter Aerts.

At least 19 recordsLinked to original sources

PubMed2007

No trade-off between biting and suction feeding performance in clariid catfishes.

It is generally assumed that biting performance trades off with suction performance in fish because both feeding types may place conflicting demands on the cranial musculo-skeletal system. However, the functional consequences of morphological adaptations enhancing biting on the mechanics and performance of suction feeding in fish remain obscure. In this study, suction feeding performance was compared between three clariid catfish species differing considerably in their biting capacity, by measuring the velocity of a standardized prey being sucked into the buccal cavity using high-speed cineradiography. In addition, buccal volume changes during prey capture were quantified by ellipse modelling. As all species were able to accelerate the prey to similar peak velocities, our results demonstrate the possibility for catfishes to increase bite performance considerably without compromising suction performance. The amount of buccal expansion in the ventral direction is approximately equal for all species. Consequently, the system generating expansion through ventral rotation of the lower jaw, hyoid and pectoral girdle is apparently not constrained (mechanically or architectonically) by the hypertrophy of the jaw adductors. As the effect of a reduced magnitude of lateral expansion (suspensorium abduction) on suction performance in Clariidae appears to be negligible (for example in Gymnallabes typus), these data demonstrate the dominant role of ventral expansion for producing suction in these fish.

Animals↗

PubMed2006

Vertical jumping performance of bonobo (Pan paniscus) suggests superior muscle properties.

Vertical jumping was used to assess muscle mechanical output in bonobos and comparisons were drawn to human jumping. Jump height, defined as the vertical displacement of the body centre of mass during the airborne phase, was determined for three bonobos of varying age and sex. All bonobos reached jump heights above 0.7 m, which greatly exceeds typical human maximal performance (0.3-0.4m). Jumps by one male bonobo (34 kg) and one human male (61.5 kg) were analysed using an inverse dynamics approach. Despite the difference in size, the mechanical output delivered by the bonobo and the human jumper during the push-off was similar: about 450 J, with a peak power output close to 3000 W. In the bonobo, most of the mechanical output was generated at the hips. To account for the mechanical output, the muscles actuating the bonobo's hips (directly and indirectly) must deliver muscle-mass-specific power and work output of 615 Wkg-1 and 92 Jkg-1, respectively. This was twice the output expected on the basis of muscle mass specific work and power in other jumping animals but seems physiologically possible. We suggest that the difference is due to a higher specific force (force per unit of cross-sectional area) in the bonobo.

Age Factors↗

PubMed2006

Hydrodynamic modelling of aquatic suction performance and intra-oral pressures: limitations for comparative studies.

The magnitude of sub-ambient pressure inside the bucco-pharyngeal cavity of aquatic animals is generally considered a valuable metric of suction feeding performance. However, these pressures do not provide a direct indication of the effect of the suction act on the movement of the prey item. Especially when comparing suction performance of animals with differences in the shape of the expanding bucco-pharyngeal cavity, the link between speed of expansion, water velocity, force exerted on the prey and intra-oral pressure remains obscure. By using mathematical models of the heads of catfishes, a morphologically diverse group of aquatic suction feeders, these relationships were tested. The kinematics of these models were fine-tuned to transport a given prey towards the mouth in the same way. Next, the calculated pressures inside these models were compared. The results show that no simple relationship exists between the amount of generated sub-ambient pressure and the force exerted on the prey during suction feeding, unless animals of the same species are compared. Therefore, for evaluating suction performance in aquatic animals in future studies, the focus should be on the flow velocities in front of the mouth, for which a direct relationship exists with the hydrodynamic force exerted on prey.

Animals↗

PubMed2006

Speed modulation in hylobatid bipedalism: a kinematic analysis.

Gibbons are highly arboreal apes, and it is expected that their bipedal locomotion will show some particularities related to the arboreal environment. Previous research has shown that, during hylobatid bipedalism, unsupported phases are rare and stride frequencies are relatively low. This study confirms previous findings, and we suggest that low stride frequencies and the absence of unsupported phases are ways to reduce disadvantageous branch oscillations during arboreal travel. Despite these restrictions, gibbons are able to locomote at a wide range of speeds, implying that they likely exploit other mechanisms to modulate their locomotor speed. To investigate this possibility, we collected video images of a large number of spontaneous bipedal bouts of four untrained white-handed gibbons by using an instrumented walkway with four synchronized cameras. These video images were digitized to obtain a quantification of the 3D kinematics of hylobatid bipedalism. We defined a large number of spatiotemporal and kinematic gait variables, and the relationship between these gait variables and (dimensionless) speed was statistically tested. It was found that gibbons mainly increase stride length to increase their locomotor speed; the main speed-modulating mechanisms are hip and ankle excursion and coupled knee and ankle extension at toe-off. Although aerial phases are rare, gibbons generally adopt a bipedal bouncing gait at most speeds and a clear-cut gait transition, as seen in human locomotion, is absent. Comparison with human and bonobo bipedalism showed that the variability of the 3D joint angles of the hind limb are comparable during human and gibbon bipedalism, and much lower than during bonobo bipedalism. The low variability found in gibbons might be related to constraints imposed by the arboreal environment. These arboreal constraints clearly affect the bipedal gait characteristics of gibbons, but do not constrain the ability to adopt a bipedal bouncing gait during terrestrial locomotion.

Animals↗

PubMed2006

Modulation and variability of prey capture kinematics in clariid catfishes.

Species with narrow or limited diets (trophic specialists) are expected to be less flexible in their feeding repertoire compared to species feeding on a wide range of different prey (trophic generalists). The ability to modulate prey capture kinematics in response to different prey types and prey position, as well as the overall variability in prey capture kinematics, is evaluated in four clariid species ranging from trophic generalist (Clarias gariepinus) to species with morphological specializations and a narrow diet (Channallabes apus and Gymnallabes typus). High-speed video recordings were made of prey captures on two prey that differ in shape, attachment strength and hardness. While the observed amount of strike-to-strike variability in prey capture kinematics is similar for all species and not influenced by prey type, only the two less specialized species showed the ability to modulate their prey capture kinematics in function of the presented prey types. All species did, however, show positional modulation during the strike by adjusting the magnitude of neurocranial elevation. These results indicate that the narrow dietary breadth of trophic specialists is indeed indicative of functional stereotypy in this group of fishes. Although most studies focussing on prey processing found a similar result, the present study is one of the few that was able to demonstrate this relationship when focussing on prey capture mechanics. Possibly, this relationship is less frequently observed for prey capture compared to prey processing because, regardless of prey type, the initial capture of prey requires a higher amount of variability.

Animals↗

PubMed2006

Evolution: a catfish that can strike its prey on land.

An important step towards understanding the evolution of terrestriality in vertebrates is to identify how the aquatic ancestors of tetrapods were able to access ground-based prey. We have discovered that the 'eel catfish' Channallabes apus, an inhabitant of the muddy swamps of tropical Africa, has a remarkable ability to forage and capture prey on land. The animal's capacity to bend its head down towards the ground while feeding seems to be an essential feature that may have enabled fish to make the transition from an aquatic to a terrestrial mode.

Africa↗

PubMed2006

Locomotor versatility in the white-handed gibbon (Hylobates lar): a spatiotemporal analysis of the bipedal, tripedal, and quadrupedal gaits.

This study gives a qualitative and quantitative description of the different terrestrial locomotor modes of a group of white-handed gibbons (Hylobates lar) from the Wild Animal Park Planckendael, Belgium. The gibbons were filmed during voluntary locomotion on a grassy and smooth substrate and on a pole. These video images allowed us to define seven different gait types, based on spatial and temporal footfall patterns. Consequent digitization of the video images (n = 254) yielded duty factors, stride lengths, and stride frequencies of the fore- and hind limbs during locomotion at a wide range of speeds. These spatiotemporal gait characteristics were regressed against velocity, and the regression lines of the different gait types were compared. In addition, gibbon bipedalism was compared with bonobo (Pan paniscus) and human bipedalism. Gibbons appear to be very versatile animals, using a bipedal, tripedal, or quadrupedal gait during terrestrial travel with an overlapping speed range. The spatiotemporal characteristics of these gaits are largely similar, although they have clearly distinct footfall patterns. Bipedal walking on the pole is slightly different from terrestrial bipedalism, but differences between substrate types (grass vs. catwalk) are subtle. During bipedalism, gibbons increase both stride length and frequency to increase speed, just as humans and bonobos do, but at a given speed, gibbons take relatively larger strides at lower rates. Bipedal walking in gibbons also appears to be relatively fast-gibbons could keep on walking at speeds where humans have to start running. Apparently, adaptations for arboreal locomotion have not constrained the terrestrial locomotor abilities of gibbons. This may indicate that the step from an arboreal ancestral ape to a terrestrial, upright bipedal hominin might not be difficult and that structural specializations are not a prerequisite for adopting a (non-habitual) bipedal gait.

Animals↗

PubMed2006

Changes in foot-function parameters during the first 5 months after the onset of independent walking: a longitudinal follow-up study.

Foot-function parameters (foot-contact patterns, oscillations of the centre of pressure (COP), peak pressures, relative vertical impulses and foot shape indices) were characterized in 10 toddlers at 1, 2, 3, 4, 6, 8, 10, 12, 16 and 20 weeks after the onset of independent walking. Significant changes were found in foot-contact patterns and COP oscillations. Improvements in balance, reflected in the decreased oscillations of the COP, coincided with changes in foot roll-over. These findings suggest that the development of a "heel-to-toe" roll-over pattern after 1 year of walking already starts early after the onset of independent walking. We could not identify any changes in load distribution underneath the plantar surface of the foot, suggesting that maturation of foot loading develops at a slower pace.

Biomechanical Phenomena↗

PubMed2006

A dynamic force analysis system for climbing of large primates.

Registering substrate reaction forces from primates during climbing requires the design and construction of customized recording devices. The technical difficulties in constructing a reliable apparatus hinder research on the kinetics of primate locomotion. This is unfortunate since arboreal locomotion, especially vertical climbing, is an important component of the hominoid locomotor repertoire. In this technical paper, we describe a custom-built climbing pole that allows recordings of dynamic 3-dimensional forces during locomotion on horizontal and sloping substrates and during vertical climbing. The pole contains an instrumented section that can readily be modified and enables us to register forces of a single limb or multiple limbs in a broad range of primates. For verification, we constructed a similar set-up (which would not be usable for primates) using a conventional force plate. Data for a human subject walking on both set-ups were compared. The experimental set-up records accurate and reliable substrate reaction forces in three orthogonal directions. Because of its adjustability, this type of modular set-up can be used for a great variety of primate studies. When combining such kinetic measurements together with kinematic information, data of great biomechanical value can be generated. These data will hopefully allow biological anthropologists to answer current questions about primate behaviours on vertical substrates.

Animals↗

PubMed2006

Take-off and landing forces in jumping frogs.

Anurans use a saltatorial (jumping) mode of locomotion. A jumping cycle can be divided into four subphases: propulsion, flight, landing and recovery. We studied the landing phase during locomotion in Rana esculenta by measuring the ground reaction forces during propulsion and landing over a range of distances. Landing performance affects locomotor ability in jumping frogs. Landing and recovery together take up one third of the locomotor cycle. Peak landing forces are on average almost three times larger than propulsive forces. The forelimbs appear to be fully extended when they make contact with the substrate and absorb the first impact peak. The height of this peak varies depending on arm positioning and jumping distance. Since the stiffness of the arms stays constant over the full jumping range, it is possible that this is a limiting factor in the ability of the forelimbs to work as dampers. A spring-dashpot model is used to model the effect of arm angle at touch down. Damping during landing is performed by placing the forelimbs at an optimal angle to cancel frictional forces effectively.

Animals↗

PubMed2006

The dynamics of hylobatid bipedalism: evidence for an energy-saving mechanism?

When gibbons travel through the forest canopy, brachiation is alternated with short bipedal bouts over horizontal boughs. We know, from previous research, that brachiation is a very efficient locomotor mode that makes use of a pendulum-like exchange of energy, but to date, nothing is known about the dynamics of hylobatid bipedalism. We wondered if gibbons also make use of an efficient gait mechanism during bipedal locomotion. To investigate this, we calculated oscillations of the centre of mass (COM), energy fluctuations, recovery rates and power outputs from the 3D ground reaction forces. These ground reaction forces were collected during spontaneous bipedal locomotion of four untrained white-handed gibbons (Hylobates lar) over an instrumented walkway (with an AMTI force plate). Excursions of the COM are relatively large during hylobatid bipedalism and the fluctuations of potential and kinetic energy are largely in-phase. Together with the low inverted pendulum recovery rates, this points to a spring-mass mechanism during bipedal locomotion. Although the well-developed Achilles tendon of gibbons seems to be a good candidate for the storage and recoil of elastic energy, this is not supported by kinematical data of the ankle joint. Instead, we suggest that the knee extensor muscle tendon unit functions as an energy-saving mechanism during hylobatid bipedalism, but detailed anatomical data is needed to confirm this suggestion. At low speeds gibbons use either pendular or spring mechanics, but a clear gait transition as seen in most quadrupedal mammals is absent. At moderate to high velocities, gibbons use a bouncing gait, generally without aerial phases. This supports the view that aerial phases are not a prerequisite for spring-mass mechanics and reinforces the claim that duty factor alone should not be used to distinguish between a walk and run.

Animals↗

PubMed2005

Changes in 3D joint dynamics during the first 5 months after the onset of independent walking: a longitudinal follow-up study.

A longitudinal follow-up study of 10 normally developing children was performed in order to identify changes in mechanical control of gait during the first months after initiation of independent walking. Changes in spatio-temporal parameters and kinematics were recorded (336 trials spread over 83 recording sessions) and linked to kinetic features of gait. At the onset of independent walking, all children in our study group showed the same walking strategy: a dominance of the extending moments around the lower extremity joints was observed and could be linked to the flexed position of the hip and knee during stance. In a subset of our study population, the dominance of the extending moments disappeared with increasing walking experience, though reversal to immature patterns was frequently observed. A linear mixed model showed that with increasing walking experience, there was an increase in dimensionless walking speed, dimensionless cadence and dimensionless stride length (without correction for the increase in speed). Maximal hip extension in stance, knee flexion and ankle plantar flexion at foot contact also increased (even when the increase in speed is taken into account). Dimensionless step width, duty factor, double support time, maximal hip flexion in swing and hip abduction significantly decreased (with correction for speed). Important changes were also observed in ground reaction force patterns, evolving towards a double "hump". No significant changes could be observed in other kinetic parameters, probably due to the high degree of variability.

Ankle Joint↗

PubMed2005

Scaling of suction feeding performance in the catfish Clarias gariepinus.

Ontogenetic changes in the absolute dimensions of the cranial system together with changes in kinematics during prey capture can cause differences in the spatiotemporal patterns of water flow generated during suction feeding. Because the velocity of this water flow determines the force that pulls prey toward and into the mouth cavity, this can affect suction feeding performance. In this study, size-related changes in the suction-induced flow patterns are determined. To do so, a mathematical suction model is applied to video recordings of prey capturing Clarias gariepinus ranging in total length from 111 to 923 mm. Although large C. gariepinus could be expected to have increasing peak velocities of water flow compared with small individuals, the results from the hydrodynamic model show that this is not the case. Yet, when C. gariepinus becomes larger, the expansive phase is prolonged, resulting in a longer sustained flow. This flow also reaches farther in front of the mouth almost proportionally with head size. Forward dynamical simulations with spherical prey that are subjected to the calculated water flows indicate that the absolute distance from which a given prey can be sucked into the mouth as well as the maximal prey diameter increase substantially with increasing head size. Consequently, the range of potential prey that can be captured through suction feeding will become broader during growth of C. gariepinus. This appears to be reflected in the natural diet of this species, where both the size and the number of evasive prey increase with increasing predator size.

Animals↗

PubMed2005

Muscle directly meets the vast power demands in agile lizards.

Level locomotion in small, agile lizards is characterized by intermittent bursts of fast running. These require very large accelerations, often reaching several times g. The power input required to increase kinetic energy is calculated to be as high as 214 W kg(-1) muscle (+/-20 W kg(-1) s.e.; averaged over the complete locomotor cycle) and 952 W kg(-1) muscle (+/-89 W kg(-1) s.e.; instantaneous peak power). In vitro muscle experiments prove that these exceptional power requirements can be met directly by the lizard's muscle fibres alone; there is no need for mechanical power amplifying mechanisms.

Acceleration↗

PubMed2005

Functional analysis of the gibbon foot during terrestrial bipedal walking: plantar pressure distributions and three-dimensional ground reaction forces.

This paper gives a detailed analysis of bipedal walking in the white-handed gibbon, based on collected pressure and force data. These data were obtained from four gibbons in the Wild Animal Park, Planckendael, Belgium, by using a walkway with integrated force plate and pressure mat. This is the first study that collects and describes dynamic plantar pressure data of bipedally walking gibbons, and combines these with force plate data. The combination of these data with previously described roll-off patterns of gibbons, based on general observations, video images, force plates, and EMG data, gives us a detailed description of foot function during gibbon bipedalism. In addition, we compare the observed characteristics of hylobatid bipedalism with the main characteristics of bonobo and human bipedalism. We found that gibbons are midfoot/heel plantigrade, and lack the typical heel-strike of other hominoids. The hallux is widely abducted and touches down at the onset of the stance phase, which results in an L-shaped course of the center of pressure. The vertical force curve is trapezoid to triangular in shape, with high peak values compared to humans. The braking component is shorter than the accelerating component, and shortens further at higher walking velocities. Speed has a significant influence on the forefoot peak pressures and on most of the defined gait parameters (e.g., vertical force peak), and it alters the foot contact pattern as well. The investigation of existing form-function relationships in nonhuman primates is essential for the interpretation of fossil remains, and might help us understand the evolution of habitual bipedal walking in hominids.

Animals↗

PubMed2005

Functional analysis of the foot and ankle myology of gibbons and bonobos.

This study investigates the foot and ankle myology of gibbons and bonobos, and compares it with the human foot. Gibbons and bonobos are both highly arboreal species, yet they have a different locomotor behaviour. Gibbon locomotion is almost exclusively arboreal and is characterized by speed and mobility, whereas bonobo locomotion entails some terrestrial knuckle-walking and both mobility and stability are important. We examine if these differences in locomotion are reflected in their foot myology. Therefore, we have executed detailed dissections of the lower hind limb of two bonobo and three gibbon cadavers. We took several measurements on the isolated muscles (mass, length, physiological cross sectional area, etc.) and calculated the relative muscle masses and belly lengths of the major muscle groups to make interspecific comparisons. An extensive description of all foot and ankle muscles is given and differences between gibbons, bonobos and humans are discussed. No major differences were found between the foot and ankle musculature of both apes; however, marked differences were found between the ape and human foot. The human foot is specialized for solely one type of locomotion, whereas ape feet are extremely adaptable to a wide variety of locomotor modes. Apart from providing interesting anatomical data, this study can also be helpful for the interpretation of fossil (pre)hominids.

Animals↗

PubMed2005

Propulsive force calculations in swimming frogs. I. A momentum-impulse approach.

Frogs are animals that are capable of locomotion in two physically different media, aquatic and terrestrial. A comparison of the kinematics of swimming frogs in a previous study revealed a difference in propulsive impulse between jumping and swimming. To explore this difference further, we determined the instantaneous forces during propulsion in swimming using an impulse-momentum approach based on DPIV flow data. The force profile obtained was compared with force profiles obtained from drag-thrust equilibrium of the centre of mass and with the force profiles generated during jumping. The new approach to quantifying the instantaneous forces during swimming was tested and proved to be a valid method for determining the external forces on the feet of swimming frogs. On the kinematic profiles of swimming, leg extension precedes propulsion. This means that it is not only the acceleration of water backwards that provides thrust, but also that the deceleration of water flowing towards the frog as a result of recovery accelerates the centre of mass prior to leg extension. The force profile obtained from the impulse-momentum approach exposed an overestimation of drag by 30% in the drag-thrust calculations. This means that the difference in impulse between jumping and swimming in frogs is even larger than previously stated. The difference between the force profiles, apart from a slightly higher peak force during jumping, lies mainly in a difference in shape. During swimming, maximal force is reached early in the extension phase, 20% into it, while during jumping, peak force is attained at 80% of the extension phase. This difference is caused by a difference in inter-limb coordination.

Animals↗

PubMed2005

Scaling of suction-feeding kinematics and dynamics in the African catfish, Clarias gariepinus.

Scaling effects on the kinematics of suction feeding in fish remain poorly understood, at least partly because of the inconsistency of the results of the existing experimental studies. Suction feeding is mechanically distinct from most other type of movements in that negative pressure inside the buccal cavity is thought to be the most important speed-limiting factor during suction. However, how buccal pressure changes with size and how this influences the speed of buccal expansion is unknown. In this paper, the effects of changes in body size on kinematics of suction feeding are studied in the catfish Clarias gariepinus. Video recordings of prey-capturing C. gariepinus ranging in total length from 111 to 923 mm were made, from which maximal displacements, velocities and accelerations of several elements of the cranial system were determined. By modelling the observed expanding head of C. gariepinus as a series of expanding hollow elliptical cylinders, buccal pressure and power requirement for the expansive phase of prey capture were calculated for an ontogenetic sequence of catfish. We found that angular velocities decrease approximately proportional with increasing cranial size, while linear velocities remain more or less constant. Although a decreasing (angular) speed of buccal expansion with increasing size could be predicted (based on calculations of power requirement and the expected mass-proportional scaling of available muscular power in C. gariepinus), the observed drop in (angular) speed during growth exceeds these predictions. The calculated muscle-mass-specific power output decreases significantly with size, suggesting a relatively lower suction effort in the larger catfish compared with the smaller catfish.

Africa↗