Free Gait Research Articles

Quadruped Free Gait Generation Based on the Primary/Secondary Gait

A free gait algorithm is proposed utilizing a new method of gait generation called primary/secondary gait. The primary gait is a fixed sequence of leg transfers with modified leg-end kinematic limits according to the obstacle presence, while the secondary gait is a flexible gait which is generated to adjust the leg-end position. The primary gait is generated considering the following four constraints: stability constraint, kinematic constraint, sequential constraint and neighboring constraints. Primary gait parameters are modified by the influence of the obstacle. Normally, the machine tends to move with the primary gait. When the primary gait cannot move the vehicle, the secondary gait is adopted to serve as a complement of the primary gait. With the proposed primary/secondary gait, it is expected to improve the efficiency of free gait generation while maintaining the mobility of the vehicle. Simulation results are given to demonstrate the efficiency of the proposed methodology.

Functional reach: Does it really measure dynamic balance?

Background: Functional reach (FR) is a new clinical measurement intended to assess dynamic balance. The purposes of this study were (1) to measure the mean FR distance in healthy elders compared with individuals with known balance impairments, (2) to analyze the extent to which FR measures dynamic balance, and (3) to describe movement strategies used during FR. Methods: Thirteen healthy elders and 15 individuals with vestibular hypofunction (VH) were tested during FR and free gait. Whole body kinematic and kinetic data including the center of gravity (CG) and center of pressure (CP) using 11 body segments and two force plates, respectively, were collected. Results: There was no difference in FR distance between healthy elders and individuals with VH. FR distance was not correlated to lateral stability measures, but was related to anterior-posterior postural control measures of FR ( r = .69 to .84) in both groups. Although FR distance strongly correlated with maximum moment arm during FR in both groups, the correlations were not as strong when the subjects were then classified by movement strategy. The mean moment arm during FR was significantly less than that of free gait. Conclusions: These data suggest FR does not measure dynamic balance; healthy elders and balance-impaired individuals with vestibular dysfunction attained the same FR distance and did so without increasing the moment arm during or at the end of FR. Recording the strategy used during FR, however, may provide other valuable information necessary in addressing balance control. Clinical implications of assessing movement strategy are discussed.

Posturography does not test vestibulospinal function

The clinical usefulness of posturography is unknown, despite its costing more than $500 per test in some areas of the United States, including Boston. We cross-sectionally and prospectively studied blinded vestibulo-ocular and vestibulospinal tests from 29 stable patients with chronic vestibular hypofunction; 22 patients were affected bilaterally (BVH), and 7 were affected unilaterally (UVH). Vestibulo-ocular function was assessed by electronystagmographic caloric stimulation and sinusoidal vertical axis rotation gains at 0.05 Hz. Vestibulospinal function was assessed by moving-platform and visual-surround posturography sensory organization tests (SOTs), paced and free gait in a gait laboratory, and clinical tests of timed gait and standing. Posturography SOT moving-platform tests 4 through 6, designed to assess vestibular function, correlated significantly ( r ≤ 0.72, P ≥ 0.01) with vestibulo-ocular tests in 5 of 6 comparisons among BVH patients. Posturography SOT results, however, correlated poorly with other vestibulospinal measures: correlations were statistically significant for only 7 of 18 comparisons with clinical balance and gait function ( r ≤ 0.69, P ≥ 0.01) and with 2 of 12 comparisons for gait laboratory dynamic stability measures ( r ≤ 0.55, P ≥ 0.01) among the BVH patients. When both the platform and visual surround moved (SOT 6), however, correlations were statistically significant with static standing clinical measures ( r = 0.51 to 0.69, P < 0.01) and with whole-body maximum moment arm during paced gait ( r = 0.55, P < 0.01). Posturography scores for the UVH patients did not significantly correlate with any vestibulo-ocular or other vestibulospinal measures. These data indicate that among patients with BVH posturography SOT scores relate at best modestly with accepted measures of vestibulo-ocular function, less well with clinical measures of balance control, and poorly with dynamic gait-performance measures. We conclude that posturography SOT does not assess vestibulospinal function. (Otolaryngol Head Neck Surg 1999;120:164-73.)

Free gait control for a quadruped walking robot

Two major approaches exist for devising gait control for a legged machine: (1) finding a sequence of leg and body movements of a robot on the basis of kinematic and possibly dynamic considerations assuming all foot placements are valid and (2) selecting leg and body movements first on the basis of feasibility of foot placements (because the underlying terrain might render impossible certain foot placements) and then accepting those that also satisfy kinematic and possibly dynamic constraints. Consider now the problem of a legged robot pursuing a quarry. With the first approach, the robot will be limited to operating over a relatively flat terrain; over such a terrain, it might be able to synthesize a sequence of precomputed straight-line and turning gaits in order to match as closely as possible to the trajectory of the quarry. If the terrain is uneven, however, the robot will have no recourse but to take the second approach, even though it is computationally more demanding. The work done so far in the second approach is limited either by the constraint that the overall direction of ambulation of the robot is known in advance or by the constraint that the foot placements are limited to the points of a grid superimposed on the topographic map of the terrain. This article presents how a free gait can be generated for following a quarry without invoking such constraints. The robot attempts to adapt constantly its direction of ambulation so that at each instant the quarry is pursued by the shortest path (although there is no guarantee that the path actually traversed by the robot is globally optimal in any sense). The directions generated by this “shortest path pursuit” prune away large segments of the search space for the discovery of appropriate foot placements. Simulated and experimental results are presented to validate the proposed gait control method. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 71–81, 1999

Free gait control for a quadruped walking robot

Two major approaches exist for devising gait control for a legged machine: (1) finding a sequence of leg and body movements of a robot on the basis of kinematic and possibly dynamic considerations assuming all foot placements are valid and (2) selecting leg and body movements first on the basis of feasibility of foot placements (because the underlying terrain might render impossible certain foot placements) and then accepting those that also satisfy kinematic and possibly dynamic constraints. Consider now the problem of a legged robot pursuing a quarry. With the first approach, the robot will be limited to operating over a relatively flat terrain; over such a terrain, it might be able to synthesize a sequence of precomputed straight-line and turning gaits in order to match as closely as possible to the trajectory of the quarry. If the terrain is uneven, however, the robot will have no recourse but to take the second approach, even though it is computationally more demanding. The work done so far in the second approach is limited either by the constraint that the overall direction of ambulation of the robot is known in advance or by the constraint that the foot placements are limited to the points of a grid superimposed on the topographic map of the terrain. This article presents how a free gait can be generated for following a quarry without invoking such constraints. The robot attempts to adapt constantly its direction of ambulation so that at each instant the quarry is pursued by the shortest path (although there is no guarantee that the path actually traversed by the robot is globally optimal in any sense). The directions generated by this “shortest path pursuit” prune away large segments of the search space for the discovery of appropriate foot placements. Simulated and experimental results are presented to validate the proposed gait control method. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 71–81, 1999

Influence of wearing complete dentures on body balance in edentulous elderly

The influence of wearing complete dentures on body balance of edentulous elderly was examined in this study. Eight edentulous volunteers (5 females and 3 males) who were satisfied with their new dentures participated in the study. Static and dynamic balance were compared between subjects with and without dentures. To evaluate static balance, path length of spontaneous postural sway with eyes closed was measured for 60 seconds using a stabilometer. To evaluate dynamic balance, gait cycle, gait velocity, and stride length during 15 meters of free gait were measured using a newly-developed gait-cycle-analyzing device and gait-speedometer. The data analysis showed that path lengths of subjects when wearing complete dentures significantly decreased compared to subjects without dentures (p < 0.05). Subjects when wearing complete dentures performed significantly faster and more stable gait compared to subjects without dentures (p < 0.05). Significant increases were concurrently observed in frequency of gait cycle and stride length (p < 0.05). The results suggested that the presence of an established occlusal vertical dimension had an influence not only on static balance but also on dynamic balance of the subjects. It was concluded that for edentulous elderly, wearing complete dentures may enhance body balance rather than not wearing a complete denture.

Gait analysis before and after unilateral total knee arthroplasty. Study using a linear regression model of normal controls — women without arthropathy

Stepwise multiple regression analysis (forward method) was performed with 22 gait variables obtained from the free and slow gait of 35 normal controls (women without knee arthropathy). These 22 variables were target variables, and velocity, age, body height, and body weight were explanatory variables. Velocity showed the greatest effect on the gait variables, followed by weight, age, and height. Of the 22 target variables, 16 could be explained by a significant level of difference of P < 0.01. A linear regression model of normal gait was then established, based on the judgment that these 16 gait variables were greatly affected by four variables — velocity, age, height, and weight. Since this model does not perfectly represent the observed values, we compared the observed value / predicted value ratios in different groups to compensate for their differences. The free gait velocity in 20 osteoarthritic patients, 1 year or more after unilateral total knee arthroplasty (TKA), and who had no pain in the contralateral knee was lower than in the normal controls. In comparisons using linear regression models, step length was shorter, step width was longer, and gait cycle was shorter than in controls. Single support time was shorter and double support time was longer. Of the ground reaction forces, the first peak of the vertical component and the peak of the driving force of the fore-aft component were smaller than in controls. The total range of motion (TRM) in the stance phase was less than in controls. These results show quantitatively not only that the velocity of gait after TKA is lower than in normal controls, but also that gait patterns are different. In eight osteoarthritic patients assessed before and after TKA, and who had no pain in the contralateral knee, free gait velocity increased 6 months post-operation, but showed no further changes at 1 year. A linear regression study comparing the gait before TKA and 6 months post-TKA revealed that step time, single support time, double support time, and step width, and — with regard to ground reaction forces — the peaks of the driving force and the braking force of the fore-aft component, and TRM in the stance phase all approached the levels in the normal controls. No further changes were observed 1 year postoperatively. Although our models were not perfect, we were able to clarify the differences in gait variables between a TKA group and normal controls and the improvements from pre- to post TKA by normalizing the influence of the four independent variables, (velocity, age, weight, and height) with particular emphasis on gait velocity.

Torque action of two-joint muscles in the swing period of stiff-legged gait: a forward dynamic model analysis

Stiff-legged gait, characterized by limited knee flexion during the swing period, is a common consequence of upper motor neuron injury. The purpose of this investigation was to determine whether the rectus femoris and hamstrings muscles (which act at both the hip and knee) contribute to stiff-legged gait if active during the swing period of the gait cycle. Ten subjects with unilateral stiff-legged gait due to stroke were evaluated. Swing period free gait data were obtained. A biomechanical model of the affected limb was developed for each subject. Muscle and tendon lengths were scaled to individual subjects while constant nominal values for maximum muscle forces were used for all subjects. Torque driven forward dynamic simulations were employed to determine the sensitivity of swing period maximum knee flexion angle to changes in hip and knee torques. Combined torque and muscle driven simulations were used to access the action of specific two-joint muscles. Both hip flexion torque and knee extension torque were found to influence knee angle, but knee angle was more sensitive to changes in torque at the knee joint. The actions of the rectus femoris and long hamstrings are most marked at the knee, although their action at the hip opposes their action at the knee. Rectus femoris activity during early swing acts to limit knee flexion and contributes to stiff-legged gait. Long hamstring activity in early swing contributes to knee flexion.

Quadruped free gait generation for straight-line and circular trajectories

A method of free gait generation is proposed utilizing the primary/secondary gait for both straight line and circular body trajectories. The primary gait is a fixed sequence of leg transfers with modified leg-ends kinematic limits according to the presence of obstacles, while the secondary gait is a flexible gait which is generated to adjust the leg-end position. The primary gait is generated considering the following four constraints: stability constraint, kinematic constraint, sequential constraint and neighboring constraints. A generalized reference coordinate (GRC) system is introduced to describe the vehicle motion. Using the GRC system, all constraints and obstacle influences are expressed by only one set of equations despite the difference of motion mode. The efficiency of free gait generation is improved with the proposed method, and the trajectory of the vehicle body can be designed more naturally. Simulation results are given to demonstrate the efficiency of the proposed methodology.

Kinematic and kinetic analysis of “la marche à petits pas”*

To better understand “la marche à petits pas”, we focused on ground reactions forces, a key interface between muscular activity and gait kinematics. Computerized recordings were used to measure kinematic and kinetic variables in 11 patients aged between 65 and 84 years and 13 control subjects aged between 65 and 86 years. Kinematics was studied with an ELITE 3D motion analysis system. Anteroposterior and vertical reaction forces were measured under each foot with three force platforms. Free gait and gait with comparable stride lengths in the patients and the control subjects were analysed. Patients displayed higher vertical displacements of toes, ankle, and knee during gait and difficulty in initiating and maintaining rhythmic stepping. In patients, the amplitude and direction of anteroposterior forces were impaired under the starting foot and under both feet during gait. Their vertical forces were weaker and less symmetrical than in control subjects at the start and while walking. Short stride lengths, high vertical foot displacements and laborious rhythm installation seem to be due to perturbations observed in amplitude and regularity of the time course in both vertical and anteroposterior ground reaction forces.

高齢者の歩行 歩行分析による検討

To observe the effects of aging on equilibrium function, a gait test using normal walking with eyes open and closed was conducted with (A) qualitative and quantitative observation by gross observation of free gait for 10 m, (B) recording by a pen oscillograph on a polygraph of 7 phenomena, namely, head movements (upward-downward: U-D, right-left: R-L, and forward-backward: F-B), activities of the bilateral soleus muscles, and bilateral foot-floor contact sequences, and (C) computer analysis: the power spectra and autocorrelations were calculated from the recordings of head move-ments and integrating activities of the bilateral soleus muscles for younger normal subjects and for elderly subjects.Conclusion1. Age-related changes in free gait are caused not only by age-related changes in the skeleto-muscular structure but also by the effects of aging on proprioceptive regulation.2. Certain changes in free gait with eyes closed were more noticeable in the elderly than in the younger group. Some elderly subjects showed no periodicity and no regularity in head movements and activities of the bilateral soleus muscles when walking with eyes closed. However, the rhythm of foot-floor contact with eyes open was generally regular. Age-related changes were not supposed to have any important effect on the central pattern generator of locomotion itself. In the elderly, the role of eyesight was considered more important to stable gait than it was in the younger group.

On the gait control of a six-legged walking machine

The paper reviews the main strategies for the leg co-ordination of a six-legged walking machine. A “free gait” algorithm is presented which allows a smooth and stable motion for an arbitrary velocity vector of the vehicle, including a rotation about the vertical axis. It consists of a rule-based central decision process, based on the analysis of a six component vector called ‘leg phase state’ The co-ordination strategy consists of preventing gait states where two neighbouring legs are lifted simultaneously. It is shown that, for a uniform translation with no spin, the free gait algorithm is optimal with respect to static stability.

Implementing and testing a reasoning-based free gait algorithm in the six-legged walking machine, “MECANT”

The paper deals with a free-gait algorithm and its implementation into a hydraulic walking machine called MECANT. The gait planner is based on heuristic rules which take into account in every planning cycle the temporal direction and velocity of motion, the availability of the legs to start a new working cycle, the stability of the machine in the direction of motion, and possible collisions between neighboring legs. The free gait considered is especially useful in conditions when the machine is executing omnidirectional motion in rough terrain. Compared to wave gait or adaptive wave gait, a more flexible motion and improved stability can be obtained. The paper includes verification experiments with a simulator, and experience with the real machine.

Implementing and Testing a Reasoning Based Free Gait Algorithm in the Six Legged Walking Machine "MECANT"

The paper deals with a free gait algorithm and its implementation into a hydraulic walking machine called MECANT. The gait planner is based on heuristic rules which take into account in every planning cycle the temporal direction and velocity of motion, availability of the legs to start a new working cycle, stability of the machine in the direction of the motion and possible collision of the neighbour legs. The free gait considered is especially useful in conditions when the machine is executing omnidirectional motion in rough terrain. Compared to wave gait or adaptive wave gait a more flexible motion and improved stability can be obtained. The paper includes verification experiments with a simulator and experiences with the real machine.

On the Gait Control of a Six-Legged Walking Machine

This paper reviews the main strategies for the leg coordination of walking machines with emphasis on the free gait. A free gait algorithm is presented which allows a smooth and stable motion for an arbitrary velocity vector of the vehicle.

Effets du vieillissement sur les capacités adaptatives locomotrices

The aim of this research was to better understand how gait slows with age. We analyzed the kinematic parameters of locomotion (velocity, stride length, cycle duration, and double support duration) and their interrelationships both in the slowing process due to aging and in intentional modulations of velocity. The experiments were carried out on a group of 67 elderly adults (aged 60 to 92) walking with a free gait and a fast gait. This group was compared to a young population in equivalent situations. The results show that the main characteristics of the elderly gait are the shortening of strides and the increasing of the double support phase. However, these properties seem to be due to the slowness of the elderly gait more than to more specific alterations affecting this population since identical features were also observed in the slow gait of the young subjects. Furthermore, the ability to intentionally modulate velocity observed in this study was not altered by aging. These results suggest that elderly gait can be said to be normal if one takes the velocity into account.

Comparative Kinematics of Two Walking Frame Gaits

Walking frames are commonly used as part of the gait rehabilitation process for a variety of clinical conditions. There has been little investigation of the characteristics of gait with such frames or of the advantages of one gait style compared with others. The kinematics of two simulated gait patterns with walking frames were investigated using conventional video analysis techniques. The purpose of the study was to compare the two gaits with respect to patterns of joint motion and temporospatial parameters. It was found that simultaneous motion of the protected limb and the frame during stepping (gait S) permitted a faster walking speed than a gait in which the frame and the protected limb were moved separately (gait D). Although the patterns of hip motion in both aided gaits differed markedly from that found in free gait, gait S encouraged more hip extension on the protected side than gait D. Since this is seen as a desirable feature in gait retraining, patients using walking frames, particularly after hip trauma, should be assessed carefully and encouraged to use gait pattern S when possible.

Terrain adaptive motion and free gait of a six-legged walking machine

A six-legged hydraulic walking machine, called MECANT I, is introduced. It has been developed for research purposes in outdoor environments. The paper describes the motion planning method used. It is based on a “top-down” approach where the vehicle body motion control is executed through the body motion planning which in turn is divided into two parts called profile tracking and terrain adaptation. The estimated support plane is used as a model of the local terrain. The kinematic constraints are included into the body path planning by applying a “plan-and-check” approach. A free gait planner based on a “state machine” approach is introduced. The planner uses a rule-based method in determination of the time instant for changing the present support pattern and in selection of the new supporting leg configuration.

001 Terrain adaptive motion and free gait of a six-leeged walking machine

001 Terrain adaptive motion and free gait of a six-leeged walking machine

高齢者の歩行

To clarify the peculiarities of gait in elderly Japanese we used a gait test which consisted of qualitative and quantitative analysis of gross observations of free walking for 10 m recorded by pen oscillography on a polygraph of 7 phenomena : 5 of which with the aid of a five-channel telemeter, head movements (upward-downward, right-left, and forward-backward), activity of both soleus muscles, and bilateral foot-floor contact sequences.The power spectrum and correlation analyses were carried out with a PDP-11 computer.1) In normal young adults, head movement recording revealed regular upward-downward movement and forward-backward inclination twice in each walking cycle and regular right-left inclination once in each walking cycle. Each soleus muscle was activated in the stance phase once in each walking cycle.2) In the elderly, the rhythm of foot-floor contact and the smooth-reciprocal swinging of the arms in free gait were often more disturbed with age when the eyes were closed than when they were open. Time required for walking 10 m, step width, and inclination length tended to increase, while cadence and step length tended to decrease with age.3) In the elderly, the irregular right-left and forward-backward sway often increased, and the pattern of soleus muscles activity during walking was irregular.These changes of free gait in the elderly are caused not only by aging changes of the skeleto-muscular structure but also by the effect of age on proprioceptive postural regulation.