Biomechanical and physiological aspects of legged locomotion in humans

Abstract

Walking and running, the two basic gaits used by man, are very complex movements. They can, however, be described using two simple models: an inverted pendulum and a spring. Muscles must contract at each step to move the body segments in the proper sequence but the work done is, in part, relieved by the interplay of mechanical energies, potential and kinetic in walking, and elastic in running. This explains why there is an optimal speed of walking (minimal metabolic cost of about 2 J.kg(-1).m(-1) at about 1.11 m.s(-1)) and why the cost of running is constant and independent of speed (about 4 J.kg(-1).m(-1)). Historically, the mechanical work of locomotion has been divided into external and internal work. The former is the work done to raise and accelerate the body centre of mass (m) within the environment, the latter is the work done to accelerate the body segments with respect to the centre of m. The total work has been calculated, somewhat arbitrarily, as the sum of the two. While the changes of potential and kinetic energies can be accurately measured, the contribution of the elastic energy cannot easily be assessed, nor can the true work performed by the muscles. Many factors can affect the work of locomotion--the gradient of the terrain, body size (height and body m), and gravity. The partitioning of positive and negative work and their different efficiencies explain why the most economical gradient is about -10% (1.1 J.kg(-1).m(-1) at 1.3 m.s(-1) for walking, and 3.1 J.kg(-1).m(-1) at between 3 and 4 m.s(-1) for running). The mechanics of walking of children, pigmies and dwarfs, in particular the recovery of energy at each step, is not different from that of taller (normal sized) individuals when the speed is expressed in dynamically equivalent terms (Froude number). An extra load, external or internal (obesity) affects internal and external work according to the distribution of the added m. Different gravitational environments determine the optimal speed of walking and the speed of transition from walking to running: at more than 1 g it is easier to walk than to run, and it is the opposite at less than 1 g. Passive aids, such as skis or skates, allow an increase in the speed of progression, but the mechanics of the locomotion cannot be simply described using the models for walking and running because step frequency, the proportion of step duration during which the foot is in contact with the ground, the position of the limbs, the force exerted on the ground and the time of its application are all different.

The apparently contradictory energetics of hopping and running: the counter-intuitive effect of constraints resolves the paradox

“…This suggests that the same mechanical and physiological features determine the cost of hopping and running, and that the original differences observed were due to differences in observational perspective created by different constraints rather than fundamental differences between the mechanics and physiology of the two activities. Kram and Taylor's (1990) force rate cost function (Eqn 1) has been successfully used to predict the relationship between gait parameters and metabolic cost for various kinds of locomotion (Weibel et al, 1992;Kram and Dawson, 1998;Kram, 2000;Saibene and Minetti, 2003;Sih and Stuhmiller, 2003). This function does a good job of predicting metabolic energy use rate over a fairly narrow range of frequencies -both when the frequencies are naturally selected in response to a constraint (as happens in speed-constrained treadmill running studies) and when the frequencies are artificially selected after the fact (as we did in the current hopping study; Fig.…”

Velocidade Autosselecionada E Ideal Da Caminhada De Amputados Transfemorais: Solo E Esteira

“…Porém, ao contrário do que acontece com indiví-duos sem restrições, os indivíduos amputados 1,27 apresentaram valores maiores para VAUS e C. Ao observar a Figura 2 podemos sugerir que o C diminui à medida que a velocidade aumenta 4 .…”

“…Em sujeitos sem restrições de caminhada, a VAUS coincide com a velocidade óti-ma (VOT), entre 4 e 4,5 km.h -1 . Nessa velocidade o sujeito apresenta menor custo de transporte (C) que é o consumo de oxigênio (VO 2 ) por metro percorrido 1 . Pesquisas a respeito da mecânica e a energética da locomoção, utilizam a esteira rolante para a realização dos seus experimentos [2][3][4][5][6][7][8] .…”

Tyrannosaurus Rex Running? Estimations of Efficiency, Speed and Acceleration

“…mg The drag-to-weight ratio 1/k can also be treated as the cost of motion, i.e. how much energy is used to move 1 N of weight to the distance of 1 m. Usually in literature, this characteristic is related to the 1 kg of mass - 1 1 Jkg m − − (see, e.g., [8]). By dividing the values in 1 1 Jkg m − − by 9.8 2 ms − (the value of gravity constant), we obtain the dimensionless criterion 1/ .…”

“…For example, the maximum metabolic rate of human athletes is approximately 2.9 m/s (28 W/kg) [8] and is 10 times greater than the capacity-efficiency of 100 m running and is in between the rate of standing 1.29 W/kg and walking 3.3 W/kg [10]. Similar large differences occur also in the case of vehicles (see [6]) and can be explained by a small value of the locomotion coefficient .…”