The walking gaits of some species of Pecora

A method is presented for defining the walking gaits of quadrupeds from films so that they can be compared in closely related species. Differences in walking patterns of 18 pecoran species belonging to four families are discussed with respect to anatomy and environment. Variation in the walk patterns of members within a species are assessed. They are found to vary often with the speed at which the walk is executed, with the terrain, with the presence of heavy horns or antlers and with age. The time taken for one walking stride increases with the increase in length of the legs, but the legs swing forward more rapidly than they would if they acted passively like cylindrical pendulums.     

Validity of the MarkWiiR for kinematic analysis during walking and running gaits

The aim of this study was to validate the MarkWiiR (MW) captured by the Nintendo Wii-Remote (100-Hz) to assess active marker displacement by comparison with 2D video analysis. Ten participants were tested on a treadmill at different walking (1<6 km · h⁻¹) and running (10<13 km · h⁻¹) speeds. During the test, the active marker for MW and a passive marker for video analysis were recorded simultaneously with the two devices. The displacement of the marker on the two axes (x-y) was computed using two different programs, Kinovea 0.8.15 and CoreMeter, for the camera and MW, respectively. Pearson correlation was acceptable (x-axis r≥0.734 and y-axis r≥0.684), and Bland–Altman plots of the walking speeds showed an average error of 0.24±0.52% and 1.5±0.91% for the x- and y-axis, respectively. The difference of running speeds showed average errors of 0.67±0.33% and 1.26±0.33% for the x- and y-axes, respectively. These results demonstrate that the two measures are similar from both the x- and the y-axis perspective. In conclusion, these findings suggest that the MarkWiiR is a valid and reliable tool to assess the kinematics of an active marker during walking and running gaits.     

Optimum walking techniques for idealized animals

The vertical component of the force exerted by a foot on the ground, in the course of a step, may rise to a single maximum and decline again (as in human running) or may show two distinct maxima (as in human walking). A foot may remain on the ground for a large or small fraction of the duration of a stride. Mathematical models are used to investigate the effects of these differences of technique on the energy cost of locomotion. The optimum technique for a biped at a given speed is different from the optimum for a hypothetical many-legged animal. The optima for quadrupedal walking are likely to lie between these extremes.
The walking techniques adopted by men at different speeds are close to the optima indicated by the bipedal model. The two maxima of the force exerted by a foot are higher, and have a lower minimum between them, at higher speeds of walking. The techniques adopted by a sheep are close to the optima indicated by the many-legged model but dogs use techniques rather closer to the optima for bipeds.
The limitations of the models are discussed.     

The metabolic cost of changing walking speeds is significant,implies lower optimal speeds for shorter distances,and increases daily energy estimates

Humans do not generally walk at constant speed, except perhaps on a treadmill. Normal walking involves starting, stopping and changing speeds, in addition to roughly steady locomotion. Here, we measure the metabolic energy cost of walking when changing speed. Subjects (healthy adults) walked with oscillating speeds on a constant-speed treadmill, alternating between walking slower and faster than the treadmill belt, moving back and forth in the laboratory frame. The metabolic rate for oscillating-speed walking was significantly higher than that for constant-speed walking (6–20% cost increase for ±0.13–0.27 m s⁻¹ speed fluctuations). The metabolic rate increase was correlated with two models: a model based on kinetic energy fluctuations and an inverted pendulum walking model, optimized for oscillating-speed constraints. The cost of changing speeds may have behavioural implications: we predicted that the energy-optimal walking speed is lower for shorter distances. We measured preferred human walking speeds for different walking distances and found people preferred lower walking speeds for shorter distances as predicted. Further, analysing published daily walking-bout distributions, we estimate that the cost of changing speeds is 4–8% of daily walking energy budget.     

Optimum walking techniques for quadrupeds and bipeds

A new theory is presented which describes quadrupedal as well as bipedal walking. It avoids errors which occurred in previous theories by evaluating separately the work done by each leg instead of deriving net work from mechanical energy fluctuations. It takes particular account of two parameters, the duty factor β (the fraction of the stride for which each foot is on the ground) and a parameter q which defines the time course of the force on each foot. It shows that for any given speed there is an optimum (β, q ) which minimizes the energy cost of locomotion. These (β, q ) are only a little different for bipeds and quadrupeds except near the critical speed at which the optimum moves abruptly from walking (high β) to running (low β). Walking men use (β, q ) close to the theoretical optima, but with slightly higher q. Walking dogs and sheep use q which are lower than the optimum values except at very low speeds. Some of the energy which would otherwise be required for locomotion may be saved by storage of elastic strain energy in tendons etc. This mechanism is more effective in running than in fast walking, which may be why men change from walking to running at lower speeds than the inelastic theory suggests.     

A study on continuous follow-the-leader (FTL) gaits: an effective walking algorithm over rough terrain

The follow-the-leader (FTL) gait is an effective walking algorithm for a legged system to traverse a rough terrain. In an FTL gait, all the legs simply place at the footprints made by the legs ahead of them. By this way the demand on foothold selection is significantly reduced. A special category of FTL gaits, called continuous FTL gaits, provide a smooth body motion during walking and enable the legged system to reach a higher speed. In this paper, a comprehensive study of continuous FTL gaits is presented. The equations for two types of continuous FTL gaits are formulated. The stability of these continuous FTL gaits is studied analytically and verified numerically. Strategies of forbidden area avoidance and special methods of large foot adjustment are introduced. The motion resulting from the use of these strategies and methods is simulated and checked using computer graphics.     

Complexity,symmetry and variability of forward and backward walking at different speeds and transfer effects on forward walking: Implications for neural control

This study aimed to investigate effects of walking direction and speed on gait complexity, symmetry and variability as indicators of neural control mechanisms, and if a period of backward walking has acute effects on forward walking. Twenty-two young adults attended 2 visits. In each visit participants walked forwards at preferred walking speed (PWS) for 3-minutes (pre) followed by 5-minutes walking each at 80%, 100% and 120% of PWS of either forward or backward walking then a further 3-minutes walking forward at PWS (post). The order of walking speed in each visit was randomised and walking direction of each visit was randomised. An inertial measurement unit was placed over L5 vertebra to record tri-axial accelerations. From the trunk accelerations multiscale entropy, harmonic ratio and stride time variability were calculated to measure complexity, symmetry and variability for each walk. Complexity increased with increasing walking speed for all axes in forward and backward walking, and backward walking was less complex than forward walking. Stride time variability was also greater in backward than forward walking. Anterio-posterior and medio-lateral complexity increased following forward and backward walking but there was no difference between forward and backward walking post effects. No effects were found for harmonic ratio. These results suggest during backward walking trunk motion is rigidly controlled but central pattern generators responsible for temporal gait patterns are less refined for backward walking. However, in both directions complexity increased as speed increased suggesting additional constraint of trunk motion, normally characterised by reduced complexity, is not applied as speed increases.     

The energy expenditure of snowshoeing in packed vs. unpacked snow at low-level walking speeds

Snowshoeing is currently ranked as one of the top 20 participatory sports in the United States, and the number of participants almost tripled, from 440,000 to 1.2 million in 1998. Despite this large increase in participation, no scientific evidence exists to quantify any physiologic response to the activity. Therefore, the purpose of this investigation was to assess the energy expenditure of snowshoeing at selected low-level speeds and evaluate its acceptability as a form of aerobic conditioning exercise. Ten habitually active subjects (7 men, 3 women, mean age = 24 +/- 3.9 years, mass = 76.6 +/- 14.5 kg, height = 173.7 +/- 9.6 cm) were recruited. Steady state heart rate data were determined from 2 treadmill tests at 4 and 6 mph. Steady state heart rates at 4 mph and 6 mph from treadmill speeds were then reproduced outdoors under 2 snow conditions, packed, and unpacked snow, while caloric expenditure and speed were determined. Expired gases were collected in Douglas bags for both snowshoe and treadmill trials and then analyzed and corrected indoors for the fractional concentrations of carbon dioxide and oxygen. Data analyses indicate that caloric expenditure during snowshoeing may be considerably higher than previously reported. Snowshoeing on packed snow at 2.95 mph elicited a similar heart rate and energy expenditure response as walking on a treadmill at 4 mph or snowshoeing in unpacked snow at 2.04 mph (Vo(2) = 18.18 +/- 0.8 ml x kg(-1) x min(-1)). Snowshoeing on packed snow at 3.97 mph elicited the same heart rate and energy expenditure response as walking on a treadmill at 6 mph or snowshoeing on unpacked snow at 2.87 mph (Vo(2) = 36.72 +/- 0.8 ml x kg(-1) x min(-1)). Furthermore, increasing walking speed on snow by just 1 mph at slow speeds (2 and 3 mph) resulted in approximately twice the energy expenditure. Our data indicate that current estimates of energy expenditure while snowshoeing underestimate by greater than 50%. Apparently the energy expenditure during snowshoeing is much higher than previously considered and varies considerably because of snow terrain. Furthermore, energy expenditure levels similar to walking can be achieved on snowshoes at much slower speeds. This study represents an original investigation into energy expenditure during snowshoeing.     

Footfall patterns and interlimb co-ordination in opossums (Family Didelphidae): evidence for the evolution of diagonal-sequence walking gaits in primates

Most primates typically use a diagonal-sequence footfall pattern during walking. This footfall pattern, which is unusual for mammals, is believed to have originated in ancestral primates in association with the use of grasping extremities for movement and foraging on thin, flexible branches. This theory was tested by comparing gait parameters between the grey short-tailed opossum Monodelphis domestica and the woolly opossum Caluromys philander , two didelphid marsupials that are strongly differentiated in grasping morphology of the extremities and in their reliance on foraging strategies involving thin branches. One hundred and thirty gait cycles were analysed quantitatively from videotapes of subjects moving quadrupedally on a runway and on poles of different diameters (7 and 28 mm). Duty factor (i.e. duration of the stance phase as a percentage of the stride period) for the forelimb and hindlimb, as well as diagonality (i.e. phase relationship between the forelimb and hindlimb cycles), were calculated for each of these symmetrical gait cycles. We found that the highly terrestrial Monodelphis , like most other non-primate mammals, relies primarily on lateral-sequence walking gaits on both runway and poles, and has relatively higher forelimb duty factors. Like primates, the highly arboreal Caluromys uses primarily diagonal-sequence walking gaits on the runway and pole, with relatively higher hindlimb duty factors and diagonality. The fact that the woolly opossum, a marsupial with primate-like feet that moves and forages mainly on thin branches, uses primarily diagonal-sequence gaits when walking supports the view that primate gaits evolved to meet the demands of locomotion on narrow supports. This also demonstrates the functional role of a grasping foot, in association with relatively higher hindlimb duty factors, protraction, and substrate reaction forces, in the production of such walking gaits.     

Assessment of the energy-related cost function over a range of walking speeds

Biomechanics and Modeling in Mechanobiology - Cost funtions are needed for calculation of muscle forces in musculoskeletal models. The behavior of the energy-related cost function, proposed by...     

Muscle contributions to support and progression over a range of walking speeds

Muscles actuate walking by providing vertical support and forward progression of the mass center. To quantify muscle contributions to vertical support and forward progression (i.e., vertical and fore-aft accelerations of the mass center) over a range of walking speeds, three-dimensional muscle-actuated simulations of gait were generated and analyzed for eight subjects walking overground at very slow, slow, free, and fast speeds. We found that gluteus maximus, gluteus medius, vasti, hamstrings, gastrocnemius, and soleus were the primary contributors to support and progression at all speeds. With the exception of gluteus medius, contributions from these muscles generally increased with walking speed. During very slow and slow walking speeds, vertical support in early stance was primarily provided by a straighter limb, such that skeletal alignment, rather than muscles, provided resistance to gravity. When walking speed increased from slow to free, contributions to support from vasti and soleus increased dramatically. Greater stance-phase knee flexion during free and fast walking speeds caused increased vasti force, which provided support but also slowed progression, while contralateral soleus simultaneously provided increased propulsion. This study provides reference data for muscle contributions to support and progression over a wide range of walking speeds and highlights the importance of walking speed when evaluating muscle function.     

Preferences for very low and very high voice pitch in humans

Manipulations of voice pitch have been shown to alter attractiveness ratings, but whether preferences extend to very low or very high voice pitch is unknown. Here, we manipulated voice pitch in averaged men's and women's voices by 2 Hz intervals to create a range of male and female voices speaking monopthong vowel sounds and spanning a range of frequencies from normal to very low and very high pitch. With these voices, we used the method of constant stimuli to measure preferences for voice. Nineteen university students (ages: 20-25) participated in three experiments. On average, men preferred high-pitched women's voices to low-pitched women's voices across all frequencies tested. On average, women preferred men's voices lowered in pitch, but did not prefer very low men's voices. The results of this study may reflect selection pressures for men's and women's voices, and shed light on a perceptual link between voice pitch and vocal attractiveness.     

Contributions of muscles to mediolateral ground reaction force over a range of walking speeds

Impaired control of mediolateral body motion during walking is an important health concern. Developing treatments to improve mediolateral control is challenging, partly because the mechanisms by which muscles modulate mediolateral ground reaction force (and thereby modulate mediolateral acceleration of the body mass center) during unimpaired walking are poorly understood. To investigate this, we examined mediolateral ground reaction forces in eight unimpaired subjects walking at four speeds and determined the contributions of muscles, gravity, and velocity-related forces to the mediolateral ground reaction force by analyzing muscle-driven simulations of these subjects. During early stance (0-6% gait cycle), peak ground reaction force on the leading foot was directed laterally and increased significantly (p<0.05) with walking speed. During early single support (14-30% gait cycle), peak ground reaction force on the stance foot was directed medially and increased significantly (p<0.01) with speed. Muscles accounted for more than 92% of the mediolateral ground reaction force over all walking speeds, whereas gravity and velocity-related forces made relatively small contributions. Muscles coordinate mediolateral acceleration via an interplay between the medial ground reaction force contributed by the abductors and the lateral ground reaction forces contributed by the knee extensors, plantarflexors, and adductors. Our findings show how muscles that contribute to forward progression and body-weight support also modulate mediolateral acceleration of the body mass center while weight is transferred from one leg to another during double support.