Mechanical and metabolic requirements for active lateral stabilization in human walking

Walking appears to be passively unstable in the lateral direction, requiring active feedback control for stability. The central nervous system may control stability by adjusting medio-lateral foot placement, but potentially with a metabolic cost. This cost increases with narrow steps and may affect the preferred step width. We hypothesized that external stabilization of the body would reduce the active control needed, thereby decreasing metabolic cost and preferred step width. To test these hypotheses, we provided external lateral stabilization, using springs pulling bilaterally from the waist, to human subjects walking on a force treadmill at 1.25 m/s. Ten subjects walked, with and without stabilization, at a prescribed step width of zero and also at their preferred step width. We measured metabolic cost using indirect calorimetry, and step width from force treadmill data. We found that at the prescribed zero step width, external stabilization resulted in a 33% decrease in step width variability (root-mean-square) and a 9.2% decrease in metabolic cost. In the preferred step width conditions, external stabilization caused subjects to prefer a 47% narrower step width, with a 32% decrease in step width variability and a 5.7% decrease in metabolic cost. These results suggest that (a). human walking requires active lateral stabilization, (b). body lateral motion is partially stabilized via medio-lateral foot placement, (c). active stabilization exacts a modest metabolic cost, and (d). humans avoid narrow step widths because they are less stable.     

Margins of stability in young adults with traumatic transtibial amputation walking in destabilizing environments

Understanding how lower-limb amputation affects walking stability, specifically in destabilizing environments, is essential for developing effective interventions to prevent falls. This study quantified mediolateral margins of stability (MOS) and MOS sub-components in young individuals with traumatic unilateral transtibial amputation (TTA) and young able-bodied individuals (AB). Thirteen AB and nine TTA completed five 3-min walking trials in a Computer Assisted Rehabilitation ENvironment (CAREN) system under each of three test conditions: no perturbations, pseudo-random mediolateral translations of the platform, and pseudo-random mediolateral translations of the visual field. Compared to the unperturbed trials, TTA exhibited increased mean MOS and MOS variability during platform and visual field perturbations (p<0.010). AB exhibited increased mean MOS during visual field perturbations and increased MOS variability during both platform and visual field perturbations (p<0.050). During platform perturbations, TTA exhibited significantly greater values than AB for mean MOS (p<0.050) and MOS variability (p<0.050); variability of the lateral distance between the center of mass (COM) and base of support at initial contact (p<0.005); mean and variability of the range of COM motion (p<0.010); and variability of COM peak velocity (p<0.050). As determined by mean MOS and MOS variability, young and otherwise healthy individuals with transtibial amputation achieved lateral stability similar to that of their able-bodied counterparts during unperturbed and visually-perturbed walking. However, based on mean and variability of MOS, unilateral transtibial amputation was shown to have affected lateral walking stability during platform perturbations.     

Intra-limb coordination while walking is affected by cognitive load and walking speed

Knowledge about intra-limb coordination (ILC) during challenging walking conditions provides insight into the adaptability of central nervous system (CNS) for controlling human gait. We assessed the effects of cognitive load and speed on the pattern and variability of the ILC in young people during walking. Thirty healthy young people (19 female and 11 male) participated in this study. They were asked to perform 9 walking trials on a treadmill, including walking at three paces (preferred, slower and faster) either without a cognitive task (single-task walking) or while subtracting 1?s or 3?s from a random three-digit number (simple and complex dual-task walking, respectively). Deviation phase (DP) and mean absolute relative phase (MARP) values—indicators of variability and phase dynamic of ILC, respectively—were calculated using the data collected by a motion capture system. We used a two-way repeated measure analysis of variance for statistical analysis. The results showed that cognitive load had a significant main effect on DP of right shank–foot and thigh–shank, left shank–foot and pelvis–thigh (p<0.05), and MARP of both thigh–shank segments (p<0.01). In addition, the main effect of walking speed was significant on DP of all segments in each side and MARP of both thigh–shank and pelvis–thigh segments (p<0.001). The interaction of cognitive load and walking speed was only significant for MARP values of left shank–foot and right pelvis–thigh (p<0.05 and p<0.001, respectively). We suggest that cognitive load and speed could significantly affect the ILC and variability and phase dynamic during walking.     

Dynamic stability of individuals with transtibial amputation walking in destabilizing environments

Lower limb amputation substantially disrupts motor and proprioceptive function. People with lower limb amputation experience considerable impairments in walking ability, including increased fall risk. Understanding the biomechanical aspects of the gait of these patients is crucial in improving their gait function and their quality of life. In the present study, 9 persons with unilateral transtibial amputation and 13 able-bodied controls walked on a large treadmill in a Computer Assisted Rehabilitation Environment (CAREN). While walking, subjects were either not perturbed, or were perturbed either by continuous mediolateral platform movements or by continuous mediolateral movements of the visual scene. Means and standard deviations of both step lengths and step widths increased significantly during both perturbation conditions (all p<0.001) for both groups. Measures of variability, local and orbital dynamic stability of trunk movements likewise exhibited large and highly significant increases during both perturbation conditions (all p<0.001) for both groups. Patients with amputation exhibited greater step width variability (p=0.01) and greater trunk movement variability (p=0.04) during platform perturbations, but did not exhibit greater local or orbital instability than healthy controls for either perturbation conditions. Our findings suggest that, in the absence of other co-morbidities, patients with unilateral transtibial amputation appear to retain sufficient sensory and motor function to maintain overall upper body stability during walking, even when substantially challenged. Additionally, these patients did not appear to rely more heavily on visual feedback to maintain trunk stability during these walking tasks.     

Lower-limb amputee recovery response to an imposed error in mediolateral foot placement

Despite walking with a wider step width, amputees remain 20% more likely to fall than non-amputees. Since mediolateral (ML) balance is critical for ambulation and contingent on ML foot placement, we used a ML disturbance to perturb walking balance and explore the influence of prosthetic foot stiffness on balance recovery. Ten transtibial amputees were fit with two commonly prescribed prosthetic feet with differing stiffness characteristics; 12 non-amputees also participated. A perturbation device that released an air burst just before heel strike imposed a repeatable medial or lateral disturbance in foot placement. After a medial disturbance, the first recovery step width was narrowed (p<0.0001) for the prosthetic limb (−103%), the sound limb (−51%) and non-amputees (−41%) and more than twice as variable. The ML inclination angle remained reduced (−109%) for the prosthetic limb, while the sound limb and non-amputees approached undisturbed levels (p<0.0004). Amputees required five steps to return to undisturbed step width after a prosthetic medial disturbance versus two steps for the sound limb and for non-amputees. After a lateral disturbance, the first recovery step was widened for the prosthetic limb (+82%), sound limb (+75%), and wider than non-amputees (+51%; p<0.0001), with all participants requiring three steps to return to undisturbed step width. Amputees also exhibited a similar upper torso response compared to the non-amputees for both disturbances. Prosthetic feet with different stiffness properties did not have a significant effect. In conclusion, amputee balance was particularly challenged by medial disturbances to the prosthetic limb implying a need for improved interventions that address these balance deficits.     

Effect of centerline-guided walking on gait characteristics in healthy subjects

One of the challenges in collecting ground reaction force (GRF) and moment data for gait analysis is to obtain “good hits” when the subject walks past the forceplates. We examined whether centerline-guided walking would significantly increase the chance of good hits and alter gait characteristics. Thirty-five healthy individuals (age: 37±13 yrs) walked on a walkway with five embedded forceplates at comfortable self-selected speeds under two conditions: (1) free walking and (2) walking along a centerline and avoiding stepping on it. Gait kinematics and GRF were collected using an 8-camera optoelectronic system and five forceplates, respectively. Surface electromyographic (EMG) activity of the rectus femoris, hamstring, gastrocnemius (GAS), and tibialis anterior (TA) were monitored bilaterally. The probability of good hits significantly increased with the centerline-guided walking (p=0.008). Repeated measures MANOVA and follow-up univariate tests revealed no significant differences between the two conditions in any of the spatiotemporal parameters except for a significant increase in step width with centerline walking (p<0.001). Centerline guiding significantly increased peak mediolateral GRF (p<0.001) and hip adduction/abduction and ankle internal/external rotation ranges of motion (p<0.01). In addition, the average EMG activity in GAS and TA during the stance phase significantly increased with the centerline walking (p<0.001). In general, the centerline walking tended to impact women more than men. Centerline-guided walking increases the chance of good hits but biomechanical characteristics of gait in the frontal and transverse planes and EMG activity should be interpreted with caution, especially in women.     

Effects of aging and arm swing on the metabolic cost of stability in human walking

To gain insight into the mechanical determinants of walking energetics, we investigated the effects of aging and arm swing on the metabolic cost of stabilization. We tested two hypotheses: (1) elderly adults consume more metabolic energy during walking than young adults because they consume more metabolic energy for lateral stabilization, and (2) arm swing reduces the metabolic cost of stabilization during walking in young and elderly adults. To test these hypotheses, we provided external lateral stabilization by applying bilateral forces (10% body weight) to a waist belt via elastic cords while young and elderly subjects walked at 1.3m/s on a motorized treadmill with arm swing and with no arm swing. We found that the external stabilizer reduced the net rate of metabolic energy consumption to a similar extent in elderly and young subjects. This reduction was greater (6-7%) when subjects walked with no arm swing than when they walked normally (3-4%). When young or elderly subjects eliminated arm swing while walking with no external stabilization, net metabolic power increased by 5-6%. We conclude that the greater metabolic cost of walking in elderly adults is not caused by a greater cost of lateral stabilization. Moreover, arm swing reduces the metabolic cost of walking in both young and elderly adults likely by contributing to stability.     

Characteristic gait patterns in older adults with obesity—Results from the Baltimore Longitudinal Study of Aging

Obesity in older adults is a growing public health problem. Excess weight causes biomechanical burden to lower extremity joints and contribute to joint pathology. The aim of this study was to identify specific characteristics of gait associated with body mass index (BMI). Preferred and maximum speed walking and related gait characteristics were examined in 164 (50–84 years) participants from Baltimore Longitudinal Study of Aging (BLSA) able to walk unassisted. Participants were divided into three groups based on their BMI: normal weight (19≤BMI<25 kg/m²), overweight (25≤BMI<30 kg/m²) and obese (BMI 30≤BMI<40 kg/m²). Total ankle generative mechanical work expenditure (MWE) in the anterior–posterior (AP) plane was progressively and significantly lower with increase in BMI for both preferred (p=0.026) and maximum speed walking (p<0.001). In the medial–lateral (ML) plane, total knee generative MWE was higher in obese participants in the preferred speed task (p=0.002), and total hip absorptive MWE was higher in obese in both preferred speed (p<0.001) and maximum speed (p=0.002) walking task compared to the normal weight participants. Older adults with obesity show spatiotemporal gait patterns that may help in reducing contact impacts. In addition, in obese persons mechanical energy usages tend to be lower in the AP plane and higher in the ML plane. Since forward progression forces are mainly implicated in normal walking, this pattern found in obese participants is suggestive of lower energetic efficiency.     

Two Independent Contributions to Step Variability during Over-Ground Human Walking

Human walking exhibits small variations in both step length and step width, some of which may be related to active balance control. Lateral balance is thought to require integrative sensorimotor control through adjustment of step width rather than length, contributing to greater variability in step width. Here we propose that step length variations are largely explained by the typical human preference for step length to increase with walking speed, which itself normally exhibits some slow and spontaneous fluctuation. In contrast, step width variations should have little relation to speed if they are produced more for lateral balance. As a test, we examined hundreds of overground walking steps by healthy young adults (N = 14, age < 40 yrs.). We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01). The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations. Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect. That difference was further magnified by walking with eyes closed, which appears detrimental to control of lateral balance. Humans appear to modulate fore-aft foot placement in precise accordance with slow fluctuations in walking speed, whereas the variability of lateral foot placement appears more closely related to balance. Step variability is separable in both direction and time scale into balance- and speed-related components. The separation of factors not related to balance may reveal which aspects of walking are most critical for the nervous system to control.     

Trunk extensor fatigue influences trunk muscle activities during walking gait

Prolonged physical activities may introduce risks for low back injury due to the adapted neuromuscular response of the system once neuromuscular fatigue is present. Trunk extensor muscles were fatigued in fourteen healthy women to observe myoelectric changes in the trunk musculature during walking trials performed before and after fatigue conditions. Sub-maximal efforts at 50% and 70% maximal trunk extension effort were performed until the pre-determined levels could not be sustained. Surface electromyography (EMG) from lumbar paraspinal (LP), rectus abdominis (RA), external oblique (EO) muscles were recorded during fatigue conditions and pre and post fatigue walking trials. Infrared sensors were used to time participants as they walked. Footswitches attached to the right heel were used to record heel contacts, and were time synchronized with the EMG signals. LP and RA activity burst peaks shifted in time at contralateral heel contacts (p < 0.05) in the 70% condition, while RA amplitude increased (p < 0.05) and EO burst peak temporal shifts (p < 0.05) were present in the 50% condition. Reduced ability of the paraspinal muscles to support the trunk after fatigue onset may be a contributing factor, lending to diminished spine stiffness in attenuating ground reaction forces.     

Men and women adopt similar walking mechanics and muscle activation patterns during load carriage

Although numerous studies have investigated the effects of load carriage on gait mechanics, most have been conducted on active military men. It remains unknown whether men and women adapt differently to carrying load. The purpose of this study was to compare the effects of load carriage on gait mechanics, muscle activation patterns, and metabolic cost between men and women walking at their preferred, unloaded walking speed. We measured whole body motion, ground reaction forces, muscle activity, and metabolic cost from 17 men and 12 women. Subjects completed four walking trials on an instrumented treadmill, each five minutes in duration, while carrying no load or an additional 10%, 20%, or 30% of body weight. Women were shorter (p<0.01), had lower body mass (p=0.01), and had lower fat-free mass (p=0.02) compared to men. No significant differences between men and women were observed for any measured gait parameter or muscle activation pattern. As load increased, so did net metabolic cost, the duration of stance phase, peak stance phase hip, knee, and ankle flexion angles, and all peak joint extension moments. The increase in the peak vertical ground reaction force was less than the carried load (e.g. ground force increased approximately 6% with each 10% increase in load). Integrated muscle activity of the soleus, medial gastrocnemius, lateral hamstrings, vastus medialis, vastus lateralis, and rectus femoris increased with load. We conclude that, despite differences in anthropometry, men and women adopt similar gait adaptations when carrying load, adjusted as a percentage of body weight.     

Redistribution of intra- and inter-limb support moments during downhill walking on different slopes

Downhill walking presents a greater risk of falling as a result of slipping or loss of balance in comparison with level walking. The current study aimed to investigate the effects of inclination angles on the intra-limb (inter-joint) and inter-limb sharing of the body support during downhill walking for a better understanding of the associated control strategy. Fifteen young male adults (age: 32.6±5.2 years, height: 168.9±5.5 cm, mass: 68.4±8.7 kg) performed level and downhill walking while their kinematic and kinetic data were measured for calculating joint moments and total support moments of the lower limbs using inverse dynamics analysis. The peak total support moments of both the leading and trailing limbs increased with increasing inclination angles (p<0.05) with different sharing patterns among individual joints. Being the major contributor to the peak total support moment during early single-limb support, the contribution of the knee remained unaltered (p>0.05), but the contributions of the hip increased with reduced contributions from the ankle (p<0.05). For the increased peak total support moment during late single-limb support, the intra-limb sharing changed from a major ankle contribution to a major knee contribution strategy. The hip contribution was also increased (p<0.05) but the hip flexor moment remained unaltered (p>0.05). During double-limb support, the main contributor to the whole body support changed from the trailing limb to the leading limb with increasing inclination angles (p<0.05).     

Walking variability during continuous pseudo-random oscillations of the support surface and visual field

Walking on uneven surfaces or while undergoing perturbations has been associated with increased gait variability in both modeling and human studies. Previous gait research involving continuous perturbations has focused on sinusoidal oscillations, which can result in individuals predicting the perturbation and/or entraining to it. Therefore, we examined the effects of continuous, pseudo-random support surface and visual field oscillations on 12 healthy, young participants. Participants walked in a virtual reality environment under no perturbation (NOP), anterior–posterior (AP) walking surface and visual oscillation and mediolateral (ML) walking surface and visual oscillation conditions. Participants exhibited shorter (p≤0.005), wider (p<0.001) and faster (p<0.001) steps relative to NOP during ML perturbations and shorter (p≤0.005) and wider (p<0.001) steps during AP perturbations. Step length variability and step width variability both increased relative to NOP during all perturbation conditions (p<0.001) but exhibited greater increases for the ML perturbations (p<0.001). Participants exhibited greater trunk position variability and trunk velocity variability in the ML direction than in the AP direction during ML perturbations relative to NOP (p<0.001). Significantly greater variability in the ML direction indicates that to maintain stability, participants needed to exert greater control in the ML direction. This observation is consistent with prior modeling predictions. The large and consistent responses observed during ML visual and walking surface perturbations suggest potential for application during gait training and patient assessment.     

Comparison of energy expenditure and substrate oxidation between walking and running in men and women

[Purpose]The present study compared energy metabolism between walking and running at equivalent speeds during two incremental exercise tests.[Methods]Thirty four university students (18 males, 16 females) were recruited. Each participant completed two trials, consisting of walking (Walk) and running (Run) trials on different days, with 2-3 days apart. Exercise on a treadmill was started from initial stage of 3 min (3.0 k/m in Walk trial, 5.0 km/h in Run trial), and the speed for walking and running was progressively every minute by 0.5 km/h. The changes in metabolic variables, heart rate (HR), and rating of perceived exertion (RPE) during exercise were compared between the trials.[Results]Energy expenditure (EE) increased with speed in each trial. However, the Walk trial had a significantly higher EE than the Run trial at speeds exceeding 92 ± 2 % of the maximal walking speed (MWS, p < 0.01). Similarly, carbohydrate (CHO) oxidation was significantly higher in the Walk trial than in the Run trial at above 92 ± 2 %MWS in males (p < 0.001) and above 93 ± 1 %MWS in females (p < 0.05).[Conclusion]These findings suggest that EE and CHO oxidation during walking increase non-linearly with speed, and walking at a fast speed causes greater metabolic responses than running at the equivalent speed in young participants.     

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.     

Human energy expenditure when walking on a moving platform

The assumption that working on board ship is more strenuous than comparable work ashore was investigated in this study. Various physiological parameters (V˙O₂, V˙CO₂, V˙ _E and HR) have been measured to determine the energy expenditure of subjects walking slowly on a moving platform (ship motion simulator). Twelve subjects (eight men and four women) walked either freely on the floor or on a treadmill at a speed of 1 m · s⁻¹. Platform motion was either in a heave, pitch or roll mode. These three conditions were compared with a control condition in which the platform remained stationary. The results showed that during pitch and roll movements of the platform, the energy expenditure for the same walking task was about 30% higher than under the stationary control condition (3.6 J · kg⁻¹ · m⁻¹ vs 2.5 J · kg⁻¹ · m⁻¹, P < 0.05) for both walking on a treadmill and free walking. The heart rate data supported the higher energy expenditure results with an elevation of the heart rate (112 beats · min⁻¹ vs 103 beats · min⁻¹, P < 0.05). The heave condition did not differ significantly from the stationary control condition. Pitch and roll were not significantly different from each other. During all experimental conditions free walking resulted in a higher energy cost of walking than treadmill walking (3.5 J · kg⁻¹ · m⁻¹ vs 2.7 J · kg⁻¹ · m⁻¹, P < 0.05) at the same average speed. The results of this experiment were interpreted as indicating that the muscular effort, needed for maintaining balance when walking on a pitching or rolling platform, resulted in a significantly higher work load than similar walking on a stable or a heaving floor, independent of the mode of walking. These results explain in part the increased fatigue observed when a task is performed on a moving platform. Accepted: 3 October 1997     

Suppression of QRFP 43 in the hypothalamic ventromedial nucleus of Long-Evans rats fed a high-fat diet

QRFP 43 is a RFamide peptide present in the ventromedial nucleus (VMN) and lateral hypothalamus. It stimulates food intake in mice and its chronic infusion induces hyperphagia, reduced thermogenesis, and obesity. In this experiment, we measured it in the VMN and lateral hypothalamus of Long-Evans rats fed either a high-fat (HF), control, or low-fat (LF) diet in parallel with plasma leptin, adiposity, and energy intake. After 8 weeks of ad libitum diet intake, energy intake of HF rats was similar to that of control rats. In the VMN, QRFP 43 was completely undetectable in HF rats and its tissue concentration in control rats was significantly lower than in LF rats (p < 0.03). HF rats had higher levels of leptin than control rats (+24%; p < 0.03) and than LF rats (+42%; p < 0.002). The QRFP 43 concentration in the VMN was inversely correlated with plasma leptin (r = −0.34; P < 0.04) and with the adipogenic index of the diet (p < 0.02) but not with insulin. We conclude that the decrease of the orexigenic drive mediated by QRFP 43 could contribute to the normalization of caloric intake in HF diet fed rats. QRFP 43 might play a role downstream of leptin in the regulation of feeding behavior.     

Species-specificity of oospore dimensions in three ecorticate species of Chara (Charales,Charophyceae)

Dimensions of oospores such as length, width, fossa-breadth, length-to-width ratio and number of striae were considered for morphological identification of the members of Charales. Oospores were collected from natural stands of three species, viz. Chara braunii, C. corallina and C. wallichii in ponds in West Bengal (India). Oospore dimensions (length, width and fossa-breadth) correlated well: though the fossa breadth–length relation of C. braunii showed lower correlation coefficient (r² = 0.076, p < 0.001), all other five breadth or width–length relationships showed r² ≥ 0.23, p < 0.001. These bivariate patterns were significantly different among the species (one-way ANCOVA of length–width ratio to fossa-breadth: adjusted means and slopes both p < 0.001), C. braunii and C. corallina has similar length to width ratios, C. wallichii and C. corallina were similar in width, whereas the species differed in breadth and length in the order C. braunii, C. wallichii, and C. corallina.     

Pygmy locomotion

The hypothesis that Pygmies may differ from Caucasians in some aspects of the mechanics of locomotion was tested. A total of 13 Pygmies and 7 Caucasians were asked to walk and run on a treadmill at 4–12 km · h^–1. Simultaneous metabolic measurements and three-dimensional motion analysis were performed allowing the energy expenditure and the mechanical external and internal work to be calculated. In Pygmies the metabolic energy cost was higher during walking at all speeds (P < 0.05), but tended to be lower during running (NS). The stride frequency and the internal mechanical work were higher for Pygmies at all walking (P < 0.05) and running (NS) speeds although the external mechanical work was similar. The total mechanical work for Pygmies was higher during walking (P < 0.05), but not during running and the efficiency of locomotion was similar in all subjects and speeds. The higher cost of walking in Pygmies is consistent with the allometric prediction for smaller subjects. The major determinants of the higher cost of walking was the difference in stride frequency (+9.45, SD 0.44% for Pygmies), which affected the mechanical internal work. This explains the observed higher total mechanical work of walking in Pygmies, even when the external component was the same. Most of the differences between Pygmies and Caucasians, observed during walking, tended to disappear when the speed was normalized as the Fronde number. However, this was not the case for running. Thus, whereas the tested hypothesis must be rejected for walking, the data from running, do indeed suggest that Pygmies may differ in some aspects of the mechanics of locomotion.