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排序方式: 共有949条查询结果,搜索用时 15 毫秒
1.
Herman Pontzer 《Biology letters》2016,12(2)
Small animals are remarkably efficient climbers but comparatively poor runners, a well-established phenomenon in locomotor energetics that drives size-related differences in locomotor ecology yet remains poorly understood. Here, I derive the energy cost of legged locomotion from two complementary components of muscle metabolism, Activation–Relaxation and Cross-bridge cycling. A mathematical model incorporating these costs explains observed patterns of locomotor cost both within and between species, across a broad range of animals (insects to ungulates), for a wide range of substrate slopes including level running and vertical climbing. This ARC model unifies work- and force-based models for locomotor cost and integrates whole-organism locomotor cost with cellular muscle physiology, creating a predictive framework for investigating evolutionary and ecological pressures shaping limb design and ranging behaviour. 相似文献
2.
Our primary objective was to examine external hip joint moments during walking in people with mild radiographic hip osteoarthritis (OA) with and without symptoms and disease-free controls. Three groups were compared (symptomatic with mild radiographic hip OA, n = 12; asymptomatic with mild radiographic hip OA, n = 13; OA-free controls, n = 20). Measures of the external moment (peak and impulse) in the sagittal, frontal and transverse plane during walking were determined. Variables were compared according to group allocation using mixed linear regression models that included individual gait trials, with group allocation as fixed effect and walking speed as a random effect. Participants with evidence of radiographic disease irrespective of symptoms walked 14–16% slower compared to disease-free controls (p = 0.002). Radiographic disease without symptoms was not associated with any altered measures of hip joint moment compared to asymptomatic OA-free controls once speed was taken into account (p ≥ 0.099). People with both mild radiographic disease and symptoms had lower external peak hip adduction moment (p = 0.005) and lower external peak internal rotation moment (p < 0.001) accounting for walking speed. Among angular impulses, only the presence of symptoms was associated with a reduced hip internal rotation impulse (p = 0.002) in the symptomatic group. Collectively, our observations suggest that symptoms have additional mechanical associations from radiographic disease alone, and provide insight into potential early markers of hip OA. Future research is required to understand the implications of modifying walking speed and/or the external hip adduction and internal rotation moment in people with mild hip OA. 相似文献
3.
Pampatheres are extinct, large‐bodied cingulates, which share morphological characters with both armadillos and glyptodonts but are considered to be more closely related to the latter. The osteoderm histology of six pampathere taxa was examined and compared to the histology of other cingulate osteoderms. This study investigates the development and functional adaptation of pampathere osteoderms as well as the phylogenetic relationships of the Pampatheriidae within the Cingulata. We found that pampathere osteoderms share a uniform histological organization based on a basic diploe‐like structure. After initial stages of intramembranous growth, metaplastic ossification, that is, the direct incorporation and mineralization of pre‐existing protein fibers, plays an important role in osteoderm development and provides information on various kinds of soft tissue otherwise not preserved. The latest stages of osteoderm growth are dominated by periosteal bone formation especially in the superficial cortex. Movable band osteoderms show regular arrangements of incorporated fibers that may increase the resistance of particularly weak areas against strain. The histological composition of pampathere osteoderms is plesiomorphic in its basic structure but shows a number of derived features. A unique array of Sharpey's fibers that are incorporated into the bone matrix at sutured osteoderm margins is interpreted as a synapomorphy of pampatheres. The arrangement of dermal fibers in the deep and superficial cortexes supports the close relationship between pampatheres and glyptodonts. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc. 相似文献
4.
Ankle and knee moment and power adaptations are elicited through load carriage conditioning in males
Soldiers routinely conduct load carriage and physical training to meet occupational requirements. These tasks are physically arduous and are believed to be the primary cause of musculoskeletal injury. Physical training can help mitigate injury risk when specifically designed to address injury mechanisms and meet task demands. This study aimed to assess lower-limb biomechanics and neuromuscular adaptations during load carriage walking in response to a 10-week evidence-based physical training program. Thirteen male civilian participants donned 23 kg and completed 5 km of load carriage treadmill walking, at 5.5 km h−1 before and after a 10-week physical training program. Three-dimensional motion capture and force plate data were acquired in over-ground walking trials before and after treadmill walking. These data were inputs to a musculoskeletal model which estimated lower-limb joint kinematics and kinetics (i.e., moments and powers) using inverse kinematics and dynamics, respectively. A two-way analysis of variance revealed significant main effect of training for kinematic and kinetics parameters at the knee and ankle joints (p < 0.05). Post-Hoc comparisons demonstrated a significant decrease (4.2%) in total negative knee power between pre- and post-March 5 km measures after training (p < 0.05). Positive power contribution shifted distally after training, increasing at the post-march measure from 39.9% to 43.6% at the ankle joint (p < 0.05). These findings demonstrate that a periodised training program may reduce injury risk through favourable ankle and knee joint adaptations. 相似文献
5.
The influence of limb alignment and transfemoral amputation technique on muscle capacity during gait
Ellyn C. Ranz Jason M. Wilken Donald A. Gajewski 《Computer methods in biomechanics and biomedical engineering》2017,20(11):1167-1174
Many factors influence successful outcomes following transfemoral amputation. One factor is surgical technique. In this study, the influence of limb alignment and surgical technique on a muscle’s capacity to generate force was examined using musculoskeletal modeling. Non-amputee and transfemoral amputee models were analyzed while hip adduction, femur length, and reattached muscle wrap position, tension and stabilization technique were systematically varied. With muscle tension preserved, wrap position and femur length had little influence on muscle capacity. However, limb alignment, muscle tension and stabilization technique notably influenced muscle capacity. Overall, myodesis stabilization provided greater muscle balance and function than myoplasty stabilization. 相似文献
6.
Olga A. Grishina Irina V. Kirillova Olga E. Glukhova 《Computer methods in biomechanics and biomedical engineering》2016,19(3):297-305
The biomechanical model of human coronary arteries was modified for improving the quality of diagnosis and surgical treatment for coronary heart disease. The problem of hemodynamics in the left coronary artery with multivessel bed disease – 45% stenosis of the anterior descending branch and 75% stenosis of the circumflex branch – was particularly considered. Numerical simulation of the coronary arterial bypass of the main trunk was carried out to estimate the functional condition of the coronary arteries after restoring myocardial blood supply by surgery. 相似文献
7.
Sharon M. Swartz 《International journal of primatology》1989,10(5):387-418
Because brachiating locomotion is characterized by a pattern of swinging movements, brachiation has often been analogized
to pendular motion, and aspects of the mechanics of pendular systems have been used to provide insight into both energetic
and structural design aspects of this locomotor mode. However, there are several limitations to this approach. First, the
motions of brachiating animals only approximate pendular motion, and therefore the energetics of these two systems are only
roughly comparable. Second, the kinematic similarity between brachiation and pendular motion will be maximal at only one velocity,
and the correspondence will be even less at greater or lesser speeds. Third, all forms of terrestrial locomotion that involve
the use of limbs incorporate elements of pendular systems, and therefore brachiation is not unusual in this respect. Finally,
it has been suggested that the mechanics of pendular motion will constrain the maximum attainable body size of brachiating
animals and that this mechanical situation explains the lack of brachiating primates of greater than 30-kg body size; the
present analysis provides evidence that the constraints on body size are far less strict than previously indicated and that
extrinsic factors such as the geometry of the forest environment are more likely to dictate maximum body size for brachiators. 相似文献
8.
Most previously published electromyographic (EMG) studies have indicated that the temporalis muscles in humans become almost
electrically quiet during incisai biting. These data have led various workers to conclude that these muscles may contribute
little to the incisai bite force. The feeding behavior and comparative anatomy of the incisors and temporalis muscles of certain
catarrhine primates, however, suggest that the temporalis muscle is an important and powerful contributor to the bite force
during incision. One purpose of this study is to analyze the EMG activity of the masseter and temporalis muscles in both humans
and macaques with the intention of focusing on the conflict between published EMG data on humans and inferences of muscle
function based on the comparative anatomy and behavior of catarrhine primates. The EMG data collected from humans in the present
study indicate that, in five of seven subjects, the masseter,anterior temporalis, and posterior temporalis muscles are very active during apple incision (i.e., relative to EMG activity
levels during apple and almond mastication). In the other two human subjects the EMG levels of these muscles are lower during
incision than during mastication, but in no instance are these muscles ever close to becoming electrically quiet. The EMG
data on macaques indicate that, in all six subjects, the masseter, anterior temporalis, and posterior temporalis muscles are
very active during incision. These data are in general agreement with inferences on muscle function that have been drawn from
the comparative anatomy and behavior of primates, but they do not agree with previous experimental data. The reason for this
disagreement is probably due to differences in the experimental procedure. In previous studies subjects simply bit isometrically
on their incisors and the resulting EMG pattern was compared to the pattern associated with powerful clenching in centric
occlusion. In the present study the subjects incised into actual food objects, and the resulting EMG pattern was compared
to the pattern associated with mastication of various foods. It is not surprising that these two procedures result in markedly
different EMG patterns, which in turn result in markedly different interpretations of jaw-muscle function. In an attempt to
explain the evolution of the postorbital septum in anthropoids, it has been suggested that the anterior temporalis is more
active than the masseter during incision (Cachel, 1979). The human and macaque EMG data do not support this hypothesis; during
incision, the two muscles show no consistent differences in humans and the masseter appears to be in fact more active than
the anterior temporalis in macaques. 相似文献
9.
Georges R. Demathieu 《Geobios》1984,17(4):439-446
Two computation methods are explained; theirobject is the estimation of the velocity of animals which are known by their footprints, and in the case of the first method, by their skeletons as well.The first method is based on the compound pendulum theory, because during the slow walking gait, the motion of the leg is similar to the oscillation of a pendulum, for the computation of the velocity (v), are considered: moment of inertia (I), radius of gyration (P) and period (T), time in seconds to cover one stride (E) in the case the maximum angle of divarication (δ) of the leg with the vertical is ≤20°. A comparison with the formula of Alexander (1976) is discussed.The second method concerns saltator animals. It is based on the fondamental laws of dynamics. With the length of the jump (E) it is possible to estimate the velocity of the trackmaker (v) and the height of the jump (K). For the vertebrates the angle of the trajectory with the horizontal plan (α) is between 20 and 45°. Thus, the result of this method is an interval of estimation in which the velocity is included.These methods do not give precise results. But these approximations supply valid informations on the velocity of extinct or living animals and can lead to the estimation of their maximum speed if the parameters E, T, vary. The problem of the errors is also discussed. It is shown that the errors in estimating the parameters have a no significant influence on the results. 相似文献
10.
Metastasis is a major, life-threatening complication of cancer. The bloodstream is the most important disseminative route
for cancer cells liberated from their parent tumors. Single circulating cancer cells are arrested in the microvasculature,
where the vast majority are killed by rapid or slow processes, and the relatively few survivors grow into micrometastases.
We review the underlying causes of one type of rapid cancer cell death in the microcirculation, namely, that caused by biomechanical
interactions of cancer cells with microvessel walls, which may result in cell surface membrane expansion and lethal rupture.
These lethal interactions appear to be important rate-regulators in hematogenous metastasis, and to dictate some aspects of
metastatic patterns. Although these are not the only interactions involving cancer cells, in contrast to others involving
cellular and humoral defense mechanisms, they have received comparatively little attention. 相似文献