Gearing effects of the patella (knee extensor muscle sesamoid) of the helmeted guineafowl during terrestrial locomotion

Human patellae (kneecaps) are thought to act as gears, altering the mechanical advantage of knee extensor muscles during running. Similar sesamoids have evolved in the knee extensor tendon independently in birds, but it is unknown if these also affect the mechanical advantage of knee extensors. Here, we examine the mechanics of the patellofemoral joint in the helmeted guineafowl Numida meleagris using a method based on muscle and tendon moment arms taken about the patella's rotation centre around the distal femur. Moment arms were estimated from a computer model representing hindlimb anatomy, using hip, knee and patellar kinematics acquired via marker‐based biplanar fluoroscopy from a subject running at 1.6 ms−1 on a treadmill. Our results support the inference that the patella of Numida does alter knee extensor leverage during running, but with a mechanical advantage generally greater than that seen in humans, implying relatively greater extension force but relatively lesser extension velocity

Contribution of finete element modeling to assessment of TMJ loading patterns.

Simulations were performed with a dynamic biochemical model of the human masticatory system that included the deformable cartilaginous structures of the temporomandibular joints as finite element models. This model predicted jaw movements as a result of force patterns of the masticatory muscles. Tension, compression and shear stresses as well as the pressure distribution were predicted during jaw open-close movements. It was found that the articular disc is able to reduce load concentrations between the articular eminence and mandibular condyle at the cost of relatively large shear stresses. Separately, predicted changes in pressure distribution inside the disc gave rise to the idea that its interstitial fluid could be subject to a continuous mixing flow pattern

Versterking van het diergezondheidsmanagement in de varkenshouderij: belemmeringen en oplossingsinrichtingen

This report presents barriers and possible solutions to strengthen the animal health management on pig farms

Sex differences in knee loading in recreational runners

Patellofemoral pain is the most common chronic pathology in recreational runners. Female runners are at greater risk of developing patellofemoral pain, although the exact mechanism behind this is not fully understood. This study aimed to determine whether female recreational runners exhibit distinct knee loading compared to males. Fifteen males and 15 females recreational runners underwent 3D running analysis at 4.0 m s−1±5%. Sagittal/coronal joint moments, patellofemoral contact forces (PTF) and pressures (PCP) were compared between sexes. The results show that females exhibited significantly greater knee extension (p<0.008, pη2=0.27: males=3.04; females=3.47 N m kg−1) and abduction (p<0.008, pη2=0.28: males=0.54; females=0.82 N m kg−1) moments as well as PTF (p<0.008, pη2=0.29: males=3.25; females=3.84 B.W.) and PCP (p<0.008, pη2=0.26: males=7.96; females=9.27 MPa) compared to males. Given the proposed relationship between knee joint loading and patellofemoral pathology, the current investigation provides insight into the incidence of patellofemoral pain in females

SEMG activity of jaw-closing muscles during biting with different unilateral occlusal supports

The aim of this study was to test the hypothesis that experimental and reversible changes of occlusion affect the levels of surface electromyographic (SEMG) activity in the anterior temporalis and masseter areas during unilateral maximal voluntary biting (MVB) in centric and eccentric position. Changes were achieved by letting 21 healthy subjects bite with and without a cotton roll between the teeth. The placement alternated between sides and between premolar and molar areas. The SEMG activity level was lower when biting in eccentric position without than with a cotton roll between teeth ( P   0·05). In the anterior temporalis area, the balancing side SEMG activity was lower in eccentric than in centric but only in molar-supported biting ( P  = 0·026). These results support that the masseter and anterior temporalis muscles have different roles in keeping the mandible in balance during unilateral supported MVB. Changes in occlusal stability achieved by biting with versus without a cotton roll were found to affect the SEMG activity levels.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79166/1/j.1365-2842.2010.02104.x.pd

The effect of varying jaw-elevator muscle forces on a finite element model of a human cranium

Finite element analyses simulating masticatory system loading are increasingly undertaken in primates, hominin fossils and modern humans. Simplifications of models and loadcases are often required given the limits of data and technology. One such area of uncertainty concerns the forces applied to cranial models and their sensitivity to variations in these forces. We assessed the effect of varying force magnitudes among jaw-elevator muscles applied to a finite element model of a human cranium. The model was loaded to simulate incisor and molar bites using different combinations of muscle forces. Symmetric, asymmetric, homogeneous and heterogeneous muscle activations were simulated by scaling maximal forces. The effects were compared with respect to strain distribution (i.e. modes of deformation) and magnitudes; bite forces and temporomandibular joint (TMJ) reaction forces. Predicted modes of deformation, strain magnitudes and bite forces were directly proportional to total applied muscle force and relatively insensitive to the degree of heterogeneity of muscle activation. However, TMJ reaction forces and mandibular fossa strains decrease and increase on the balancing and working sides according to the degree of asymmetry of loading. These results indicate that when modes, rather than magnitudes, of facial deformation are of interest, errors in applied muscle forces have limited effects. However the degree of asymmetric loading does impact on TMJ reaction forces and mandibular fossa strains. These findings are of particular interest in relation to studies of skeletal and fossil material, where muscle data are not available and estimation of muscle forces from skeletal proxies is prone to error. This article is protected by copyright. All rights reserved