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Biomedical subjects

Brigitte Demes

Publications and source records attributed to Brigitte Demes.

5 recordsLinked to original sources
PubMed2005

Gait mechanics of lemurid primates on terrestrial and arboreal substrates.

Aspects of gait mechanics of two lemurid species were explored experimentally. Substrate reaction forces were recorded for three animals each of L. catta and E. fulvus walking and running at voluntary speeds either on a wooden runway with an integrated force platform or on elevated pole supports with a section attached to the force platform. The average height of the back over these substrates and fluctuations in this height were evaluated using video-analysis. Animals preferred walking gaits and lower speeds on the poles, and gallops and higher speeds on the ground. At overlapping speeds, few adjustments to substrate types were identified. Hind limb peak forces are usually lower on the poles than on the ground, and the caudal back is closer to the substrate. This suggests that greater hind limb flexion and reduced limb stiffness occurred on the poles. The support phases for both limbs at higher speeds are slightly elongated on the poles. Forelimb peak forces are not lower, and the trajectory of the caudal back does not follow a smoother path, i.e., not all elements of a compliant gait are present on the simulated arboreal substrates. The horizontal, rigid poles, offered as substitutes for branchlike supports in the natural habitat, may not pose enough of a challenge to require more substantial gait adjustments. Across substrates, forelimb peak forces are generally lower than hind limb peak forces. The interlimb force distribution is similar to that of most other primates with more even limb lengths. Walking gaits present a greater divergence in fore- and hind limb forces than galloping gaits, which are associated with higher forces. The more arboreal E. fulvus has higher forelimb forces than the more terrestrial L. catta, unlike some anthropoid species in which the arborealists have lower forelimb forces than the terrestrialists. As in other primate and nonprimate quadrupeds, the major propulsive thrust comes from the hind limbs in both lemurs. While our data confirm certain aspects of primate gait mechanics (e.g., generally higher hind limb forces), they do not fully support the notion of greater limb compliance. Neither a compliant forelimb on branchlike supports, nor a negative correlation of forelimb force magnitudes with degree of arboreality were observed. Increasing forelimb-to-hind-limb-force-ratios with increasing speed and force magnitudes are also not expected under this paradigm.

Analysis of Variance↗
PubMed2005

External forces on the limbs of jumping lemurs at takeoff and landing.

Ground reaction forces were recorded for jumps of three individuals each of Lemur catta and Eulemur fulvus. Animals jumped back and forth between a ground-mounted force plate and a 0.5-m elevated platform, covering horizontal distances of 0.5-2 m. In total, 190 takeoffs and 263 landings were collected. Animals typically jumped from a run up and into a run out, during which they gained or into which they carried horizontal impulse. Correspondingly, vertical impulses dominated takeoffs and landings. Peak forces were moderate in magnitude and not much higher than forces reported for quadrupedal gaits. This is in contrast to the forces for standing jumps of specialized leapers that considerably exceed forces associated with quadrupedal gaits. Force magnitudes for the lemur jumps are more comparable to peak forces reported for other quadrupeds performing running jumps. Takeoffs are characterized by higher hindlimb than forelimb peak forces and impulses. L. catta typically landed with the hindlimbs making first contact, and the hindlimb forces and impulses were higher than the forelimb forces and impulses at landing. E. fulvus typically landed with the forelimbs striking first and also bearing the higher forces. This pattern does not fully conform to the paradigm of primate limb force distribution, with higher hindlimb than forelimb forces. However, the absolute highest forces in E. fulvus also occur at the hindlimbs, during acceleration for takeoff.

Animals↗
PubMed2004

Predicting long bone loading from cross-sectional geometry.

Long bone loading histories are commonly evaluated using a beam model by calculating cross-sectional second moments of areas (SMAs). Without in vivo strain data, SMA analyses commonly make two explicit or implicit assumptions. First, while it has long been known that axial compression superimposed on bending shifts neutral axes away from cross-sectional area centroids, most analyses assume that cross-sectional properties calculated through the area centroid approximate cross-sectional strength. Second, the orientation of maximum bending rigidity is often assumed to reflect the orientation of peak or habitual bending forces the bone experiences. These assumptions are tested in sheep in which rosette strain gauges mounted at three locations around the tibia and metatarsal midshafts measured in vivo strains during treadmill running at 1.5 m/sec. Calculated normal strain distributions confirm that the neutral axis of bending does not run through the midshaft centroid. In these animals, orientations of the principal centroidal axes around which maximum SMAs (Imax) are calculated are not in the same planes in which the bones experienced bending. Cross-sectional properties calculated using centroidal axes have substantial differences in magnitude (up to 55%) but high correlations in pattern compared to cross-sectional properties calculated around experimentally determined neutral axes. Thus interindividual comparisons of cross-sectional properties calculated from centroidal axes may be useful in terms of pattern, but are subject to high errors in terms of absolute values. In addition, cross-sectional properties do not necessarily provide reliable data on the orientations of loads to which bones are subjected.

Anatomy, Cross-Sectional↗
PubMed2003

Optimization of bone growth and remodeling in response to loading in tapered mammalian limbs.

How bones respond dynamically to mechanical loading through changes in shape and structure is poorly understood, particularly with respect to variations between bones. Structurally, cortical bones adapt in vivo to their mechanical environments primarily by modulating two processes, modeling and Haversian remodeling. Modeling, defined here as the addition of new bone, may occur in response to mechanical stimuli by altering bone shape or size through growth. Haversian remodeling is thought to be an adaptation to repair microcracks or prevent microcrack propagation. Here, we examine whether cortical bone in sheep limbs modulates periosteal modeling and Haversian remodeling to optimize strength relative to mass in hind-limb midshafts in response to moderate levels of exercise at different growth stages. Histomorphometry was used to compare rates of periosteal growth and Haversian remodeling in exercised and sedentary treatment groups of juvenile, subadult and young adult sheep. In vivo strain data were also collected for the tibia and metatarsal midshafts of juvenile sheep. The results suggest that limb bones initially optimize responses to loading according to the varying power requirements associated with adding mass at different locations. In juveniles, exercise induces higher rates of periosteal modeling in proximal midshafts and higher rates of Haversian remodeling in distal midshafts. Consequently, distal element midshafts experience higher strains and, presumably, have lower safety factors. As animals age, periosteal modeling rates decline and Haversian remodeling rates increase, but moderate levels of mechanical loading stimulate neither process significantly.

Animals↗