Low leg compliance permits grounded running at speeds where the inverted pendulum model gets airborne (original) (raw)
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Race Walking Ground Reaction Forces at Increasing Speeds: A Comparison with Walking and Running
Symmetry
Race walking has been theoretically described as a walking gait in which no flight time is allowed and high travelling speed, comparable to running (3.6–4.2 m s−1), is achieved. The aim of this study was to mechanically understand such a “hybrid gait” by analysing the ground reaction forces (GRFs) generated in a wide range of race walking speeds, while comparing them to running and walking. Fifteen athletes race-walked on an instrumented walkway (4 m) and three-dimensional GRFs were recorded at 1000 Hz. Subjects were asked to performed three self-selected speeds corresponding to a low, medium and high speed. Peak forces increased with speeds and medio-lateral and braking peaks were higher than in walking and running, whereas the vertical peaks were higher than walking but lower than running. Vertical GRF traces showed two characteristic patterns: one resembling the “M-shape” of walking and the second characterised by a first peak and a subsequent plateau. These different patterns we...
McMahon Cheng 1990 J BioMech "Leg Stiffness & Running Speed Effects"
Abslract-A mathematical model for terrestrial running is presented, based on a leg with the properties of a simple spring. Experimental force-platform evidence is reviewed justifying the formulation of the model. The gov$ming differential equations are given in dimensionless form lo make the results representative of animals bfall body sizes. The dimensionless input parameters are: f./, a horizontal Froude number based on forward speed and leg length; I'. a vertical Froude number based on vertical landing velocity and leg length, and KLeP, a dimensionless stiffness for the leg-spring. Results show that at high forward speed, K,,, is a nearly liiear function of both U and V, while the eflective vertical stitTness is a quadratic function of U. For each U. V pair. the simulation shows that the vertical force al mid-step may be minimized by the choice of a particuldr step length. A particularly useful specification of the theory occurs when both KLEo and t' are assumed~fined. When K,,o= IS and Y=O.18. Ihe model makes predictions of relative stride length S and initial leg angle 8, (hat are in good agreement with experimental data obtained from the literature. NOhlENCLATl'RF: Dimcwsional sarichles 21, sin 0, 1. 1, "-v X Y maximum vertical force horizlontal force on mass vertical foxy on mass spring stiffness of leg cl%xlivc vertical stilTncss (same as k,,, in Ihc cast of vertical hopping; otherwise dikrcnt) instantaneous length of leg [Fig. 2(h) J starling and ending leg length body mass stride length, distance between footprints of same fool step kngth. distance moved during one contact period time in air time of contact horizontal velocity at beginning of contact vertiaal velocity at beginning of contact horizbntal coordinate of body mass [Fig. 2(b)] verridal coordinate of body mass [Figs 2(a) and I'31 Dimensionless variables dimensionless vertical acceleraGon dimensionless leg sriflncss dimensionless vertical sMness dimensionless leg length relative stride length horizontal Froude number vertical Froude number Groucho number lSTROOUCTlON This paper presents a simple yet comprehensive theory for runhing in terrestrial animals. We first review experimental evidence justifying our main assumption , that the leg is a spring. Then we give a series of results predicting important parameters such as the peak ground reaction force and the stride length. Finally. we compare these predictions with published experiments. We seek the simplest model of running capable of explaining how the stiffness of the leg spring couples with speed. Before beginning. however. it is useful to ask an even more basic question: what distinguishes walking and running? At lirst glance, the diffcrencc bctwccn walking and running in terrestrial animals would appear obvious. In running, all feet are in the air at some point in the gait cycle, whereas in walking there is always at least one foot on the ground. This distinction is appropriate most of the time for most animals, but thcrc are times when it fails. When humans run along a circular path, the aerial phase of the motion disappears if the turn has a sufficiently small radius (Greene and McMahon, 1979a). When humans run on a treadmill at constant speed but deliberately bend their knees more than usual in order to decrease the vertical stiffness of the legs and body, again the aerial phase is found to disappear when the extra knee Aexion is great enough (McMahon et al., 1987). A better criterion for distinguishing between walking and running is the one put forward by Cavagna et nl. (1976). On the basis of observations in humans, they pointed out that in walking, the center of mass is highest in mid-step, when the hip of the stance leg passes over the ankle. In running, by comparison, the center of mass is lowest at mid-step. Thus in walking, but not in running, gravitational potential energy is stored in the lirst half of the walking step as the center of mass rises, and returned in the form of kinetic energy during the second half of the step as the center of mass falls. Cavagna et ol. (1976) emphasized that in running, changes of forward kinetic energy and gravitational potential energy are in phase and therefore cannot exchange with one another to smooth out fluctuations 65
European Journal of Applied Physiology, 2020
Purpose Much like running on a slope, running against/with a horizontal traction force which either hinders/aids the forward motion of the runner creates a shift in the positive and negative muscular work, which in turn modifies the bouncing mechanism of running. The purpose of the study is to (1) investigate the energy changes of the centre of mass and the storage/release of energy throughout the step during running associated with speed and increasing hindering and aiding traction forces; and (2) compare these changes to those observed when running on a slope. Methods Ground reaction forces were measured on eight subjects running on an instrumented treadmill against different traction forces at different speeds. Results As compared to unperturbed running, running against/with a traction force increases/decreases positive external work by ~ 20-70% and decreases/increases negative work by ~ 40-60%, depending on speed and traction force. The external power to maintain forward motion against a traction is contained by increasing the pushing time and step frequency. When running with an aiding force, the external power during the brake is limited by increasing braking time. Furthermore, the aerial time is increased to reduce the power required to reset the limbs each step. Conclusion Our results show that the bouncing mechanism of running against/with a hindering/aiding traction force is equivalent to that of running on a positive/negative slope.
Skipping on uneven ground: trailing leg adjustments simplify control and enhance robustness
Royal Society Open Science, 2018
It is known that humans intentionally choose skipping in special situations, e.g. when descending stairs or when moving in environments with lower gravity than on Earth. Although those situations involve uneven locomotion, the dynamics of human skipping on uneven ground have not yet been addressed. To find the reasons that may motivate this gait, we combined experimental data on humans with numerical simulations on a bipedal spring-loaded inverted pendulum model (BSLIP). To drive the model, the following parameters were estimated from nine subjects skipping across a single drop in ground level: leg lengths at touchdown, leg stiffness of both legs, aperture angle between legs, trailing leg angle at touchdown (leg landing first after flight phase), and trailing leg retraction speed. We found that leg adjustments in humans occur mostly in the trailing leg (low to moderate leg retraction during swing phase, reduced trailing leg stiffness, and flatter trailing leg angle at lowered touchdown). When transferring these leg adjustments to the BSLIP model, the capacity of the model to cope with sudden-drop perturbations increased. 1 In our paper gait asymmetry should not be understood in the sense of Hildebrand (time-(a) symmetry, [6]), rather that leg movements and mechanics of one side are not exactly repeated on the other side.
Landing-Takeoff Asymmetries Applied to Running Mechanics: A New Perspective for Performance
Frontiers in Physiology
Background: Elastic bouncing is a physio-mechanical model that can elucidate running behavior in different situations, including landing and takeoff patterns and the characteristics of the muscle-tendon units during stretch and recoil in running. An increase in running speed improves the body's elastic mechanisms. Although some measures of elastic bouncing are usually carried out, a general description of the elastic mechanism has not been explored in running performance. This study aimed to compare elastic bouncing parameters between the higher-and lower-performing athletes in a 3000 m test. Methods: Thirty-eight endurance runners (men) were divided into two groups based on 3000 m performance: the high-performance group (P high ; n = 19; age: 29 ± 5 years; mass: 72.9 ± 10 kg; stature: 177 ± 8 cm; 3000 time : 656 ± 32 s) and the lowperformance group (P low ; n = 19; age: 32 ± 6 years; mass: 73.9 ± 7 kg; stature: 175 ± 5 cm; 3000 time : 751 ± 29 s). They performed three tests on different days: (i) 3000 m on a track; (ii) incremental running test; and (iii) a running biomechanical test on a treadmill at 13 different speeds from 8 to 20 km h −1. Performance was evaluated using the race time of the 3000 m test. The biomechanics variables included effective contact time (t ce), aerial time (t ae), positive work time (t push), negative work time (t break), step frequency (f step), and elastic system frequency (f sist), vertical displacement (S v) in t ce and t ae (S ce and S ae), vertical force, and vertical stiffness were evaluated in a biomechanical submaximal test on treadmill. Results: The t ae , f sist , vertical force and stiffness were higher (p < 0.05) and t ce and f step were lower (p < 0.05) in P high , with no differences between groups in t push and t break. Conclusion: The elastic bouncing was optimized in runners of the best performance level, demonstrating a better use of elastic components.
2021
The current study aimed to evaluate the effects of barefoot and shod running with two different styles on ground reaction force-frequency content in recreational runners with low arched feet. Methods: The statistical sample of this research was 13 males with Pronated Feet (PF) (Mean±SD age: 26.2±2.8 y; height: 176.1±8.4 cm; weight: 78.3±14.3 kg). A force plate (Bertec, USA) with a sample rate of 1000 Hz was used to record the reaction forces under each foot. Three test conditions in our study included shod running with rearfoot, midfoot, and forefoot patterns. Repeated-measures Analysis of Variance (ANOVA) was used for analyzing the data. Results: During forefoot running, the research subjects attained 10% higher GRF values in vertical direction, compared with rearfoot running (P˂0.001, d=2.133). Forefoot running decreased the peak vertical GRF, compared to rearfoot running (by 12%, P=0.01, d=0.826). Barefoot running decreased the peak vertical GRF, compared to shod running (by 6%, P=0.027, d=1.143). The collected results revealed a significantly lower FyMed (P<0.
Parameter identification for vertical ground reaction forces on feet while running
Sports Engineering, 2015
The human foot is subjected to ground reaction forces during running. These forces have been studied for decades to reduce the related injuries and increase comfort. A four-degree-of-freedom system has been used in the literature to simulate the human body motion during the touchdown. However, there are still inconsistencies between the simulation results and experimental measurements. In this study, an optimization technique is proposed to obtain the required parameters to estimate the vertical ground reaction force using the measurements from actual runners. The touchdown velocities of the rigid and wobbling body masses were also treated as optimization variables. It was shown that the proposed parameters can be adjusted to represent a particular shoe type. Specifically, vertical ground reaction force parameters and touchdown velocities were obtained for shoes with various insole properties and cushioning technologies. The results of this study suggest that the human locomotion system reacts to the shoe properties by regulating the velocities of the body wobbling and rigid masses. The magnitude and the load rate obtained using the proposed parameters are consistent with the experimental data. It is shown that the viscoelastic properties of the shoe will significantly affect the load rate but not the load magnitude.