1,721,059 research outputs found
Contraction dynamics in antagonist muscles
No full textBy taking into account the torque/angle and the torque/angular speed relationships of antagonist muscles acting across a joint it is possible to predict the contraction dynamics when they are simultaneously activated at a constant level. The simulation is displayed in a "phase-plane" where trajectories for each starting condition (angle--abscissa, angular speed--ordinate) represent the contraction dynamics. The results vary in the position of attractors, repulsors and trajectory shapes. Attractor points (at zero speed) have particular significance in joint stabilization. It was found that with certain reciprocal torque/angle relationships of antagonist muscles, a range of stable joint angles can be quickly reached just by selecting the proper group activation level. A given ratio between the activation levels selects the stable joint angle (attractor) while the overall amplitude will set the joint stiffness in that position. Thus a hypothesized control system should choose just two neural activation amplitudes (time-course considerations are unnecessary), with a reduction of the information needed to stiffen the joint. Furthermore, even ignoring the effects of joint friction, the trajectories toward attractors showed a tendency to cross the zero speed boundary no more than once, resembling the behaviour of an overdamped spring-dashpot system. A couple of testing simulations demonstrated that the combination of non-linear torque/angle and torque/speed relationships is essential to avoid tremor-like paths about the equilibrium and to quickly stiffen the joint. Other aspects related to co-contractions are discussed in the paper
Passive tools for enhancing muscle-driven motion and locomotion
No full textMusculo-skeletal systems and body design in general have evolved to move effectively and travel in specific environments. Humans have always aspired to reach higher power movement and to locomote safely and fast, even through unfamiliar media (air, water, snow, ice). For the last few millennia, human ingenuity has led to the invention of a variety of passive tools that help to compensate for the limitations in their body design. This Commentary discusses many of those tools, ranging from halteres used by athletes in ancient Greece, to bows, skis, fins, skates and bicycles, which are characterised by not supplying any additional mechanical energy, thus retaining the use of muscular force alone. The energy cascade from metabolic fuel to final movement is described, with particular emphasis on the steps where some energy saving and/or power enhancement is viable. Swimming is used to illustrate the efficiency breakdown in complex locomotion, and the advantage of using fins. A novel graphical representation of world records in different types of terrestrial and aquatic locomotion is presented, which together with a suggested method for estimating their metabolic cost (energy per unit distance), will illustrate the success of the tools used
Bioenergetics and biomechanics of cycling: the role of ‘internal work’
No full textThe 'dissection' of energy expenditure of cycling into the metabolic equivalent of the different forms of mechanical work done, inaugurated 30 years ago by di Prampero and collaborators, has been much debated in the last few decades. The mechanical internal work, particularly, which is currently associated to the movement of the lower limbs, has been approached, estimated and discussed in several different ways and there is no agreed consensus on its role in cycling. This paper, through re-processing previously published data of oxygen consumption during pedalling at different frequency, external load and limb mass, proposes a model equation and a multiple non-linear regression as the method to assess the internal work of cycling. With that tool a very consistent metabolic equivalent of the internal work is obtained. However, a software simulation of pedalling limbs showed, as suggested in the literature, that the link with the chain ring allows the system to passively revolve forever, after an initial push. This result challenges the very existence of the 'kinematic internal work' of cycling. We conclude and suggest that the 'viscous internal work', an often neglected and almost unmeasurable portion of the internal work that could be proportional to the 'kinematic' form, is responsible for the extra metabolic expenditure as measured when the pedalling frequency of cycling increases
Optimum gradient of mountain paths
No full textBy combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained prediction
Biomechanical determinants of transverse and rotary gallop in mammals
No full textIn transverse gallop, the placement of the second hind foot is followed by that of the contralateral forefoot, while in rotary gallop it is followed by the ipsilateral forefoot, and the sequence of footfalls appears to rotate around the body. Three-hundred-and-fifty-one filmed sequences have been analysed to assess the gallop type of 89 investigated mammal species belonging to the Carnivora, Artiodactyla and Perissodactyla orders. Twenty-three biometrical, ecological and physiological parameters have been collected for each species, both from literature data and from experimental measures.
Most of the species showed only one kind of gallop: transverse (40%) or rotary (39%). Some species performed rotary gallop only at high speed (17%), while a small number showed both kinds of gallop at any speed (4%). Two main principal components extracted by PCA accounted for size (PC1) and velocity (PC2), with the latter associated with the rotary galloper group. A canonical correlation analysis showed a significant separation of the two groups on the second canonical function (F = 14.2; d.f. = 1; p < 0.001), mainly based on the metacarpus/humerus and metatarsus/femur length ratio. The gait pattern analysis provided significant differences between transverse and rotary gallop in fore and hind duty factor (t-test; p < 0.001), and in duration of the fore contact (t-test; p < 0.001).
Our results assessed the typical gallop gait in the investigated species and confirmed the correlation between cursoriality and rotary gallop and identified some morphological characters correlated with the gallop type
Gaits at high speed in free ranging cursorial mammals
No full textTerrestrial mammals with vertically oriented limbs moving in a parasagittal plane, and generally larger than 1 kg of body mass, are defined “cursorial”. Most of them belong to the orders Carnivora, Artiodactyla and Perissodactyla, which comprehend the fastest terrestrial mammals: the cheetah, the fastest land animal on sprint, and the pronghorn, the fastest land animal on long distance.
Cursorial mammals can be preys or predators, living in open or mixed habitats and different terrains. We investigated the two high-speed gait used by cursorial species, transverse and rotary gallop, from both biomechanical and functional point of view. In transverse gallop the placement of the second hind foot is followed by that of the controlateral forefoot, while in rotary gallop it is followed by the ipsilateral forefoot, and the sequence of footfalls appears to rotate around the body. 351 sequences, filmed in the wild, have been analysed to assess the gallop type of 89 investigated mammal species belonging to the three mentioned orders. Biometrical, ecological and physiological parameters have been collected for each species both from literature data and from experimental measures.
Non-parametrical statistical analyses, using 10000 sampled tables with Monte Carlo simulation, indicated that transverse “horse-like” gallop was significantly more frequent in diurnal, gregarious species that live in open habitats, such as grasslands and plains. Rotary “cheetah-like” gallopers resulted significantly more frequent among crepuscular, solitary predator species that live in more mixed habitats. Around 20% of the investigated species, mainly canids, pronghorns and some antelopes, performed transverse gallop at slow speed and rotary gallop at higher speed.
Our results indicated a strictly relationship among body shape, gait, speed and manoeuvrability. Rotary gallop, gait adopted by the majority of fast-running mammals, gives also the advantage of higher manoeuvrability at any speed, especially useful when running on rugged terrains in mixed habitats. Larger bodies advantage species that live in open habitat, like grasslands and deserts, with the consequences of less agility and less spine flexibility. Among these species transverse gallop is prevailing. Some gregarious preys and cooperative predators, which live in grasslands and savannahs, have to balance the needs for high endurance, strength and longer limbs to run faster. More likely they show a speed dependent gallop pattern
Hopping locomotion at different gravity : metabolism and mechanics in humans
No full textPrevious literature on the effects of low gravity on the mechanics and energetics of human locomotion already dealt with walking, running and skipping. The aim of the present study is to obtain a comprehensive view on that subject by including measurements of human hopping in simulated low gravity, a gait often adopted in many Apollo Missions and documented in NASA footage. Six subjects hopped at different speeds at terrestrial, Martian and Lunar gravity on a treadmill while oxygen consumption and 3D body kinematic were sampled. Results clearly indicate that hopping is too metabolically expensive to be a sustainable locomotion on Earth but, similarly to skipping (and running), its economy greatly (more than x10) increases at lower gravity. On the Moon, the metabolic cost of hopping becomes even lower than that of walking, skipping and running, but the general finding is that gaits with very different economy on Earth share almost the same economy on the Moon. The mechanical reasons for such a decrease in cost are discussed in the paper. The present data, together with previous findings, will allow also to predict the aerobic traverse range/duration of astronauts when getting far from their base station on low gravity planets
A model equation for the prediction of mechanical internal work of terrestrial locomotion
No full textBy refining a previously published model, a simple equation for the estimation of the mechanical internal work during locomotion is presented. The only input variables are the progression speed, the stride frequency and the duty factor, i.e. the fraction of the stride duration at which a foot is in contact with the ground. The inclusion of this last variable, easily measurable, allows to obtain a single equation for both walking and running. The model predictions have been compared with the mechanical internal work experimentally obtained on humans in several conditions: speeds (range 0.8–3.3ms-1), gaits (walking and running) and gradients (±15%). The close match between the two indicates that the model equation can be used whenever a direct measurement of the mechanical internal work is unavailable
Optimal interval for periodical lead limb changes during straight gallop in race horses
No full textIn transverse gallop the leading feet (i.e. the second limb of each pair on the ground) of hind and forelimbs are ipsilateral. Therefore, we can distinguish a right-leading by a left-leading gallop.
When turning, a horse leads with its inside limbs. Consequently, during direction changes, right-hand bends are covered using right-leading gallop and vice-versa. Even if there are preferences for the leading foot on straights, probably due to individual asymmetries of the body, we also observe periodical lead changes. Potential reasons for those are: a) the interaction between the shoulder and the thoraco-pulmonar complex, which is maximum during the lead leg support, and b) musculo-skeletal stress induced by the gait asymmetry (the trunk sagittal plane deviated from the progression plane by 3o, pers. obs.).
Also by considering that the lead change discontinuity on straights is expected to decrease gallop performance, we hypothesized that there should be a consistently “optimal” number of strides or distance between lead changes.
From the analysis of 84 horse-race videos of different tracks in Italy, we found that 48 ± 20 strides were covered between two successive lead changes on straights. As expected, race distance, the number of bends to be covered and, possibly, the 'rider-factor' influenced the number of changes. The predominant leading leg used on straightaways is significantly different from that employed during bends in both clockwise and counter-clockwise racetracks
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