Biofeedback augmenting lower limb loading alters the underlying temporal structure of gait following anterior cruciate ligament reconstruction

Biofeedback has recently been explored to target deviant lower extremity loading mechanics following anterior cruciate ligament reconstruction (ACLR) to mitigate the development of post traumatic osteoarthritis. The impact this feedback has on the structure of the stride interval dynamics—a barometer of gait system health—however, have yet to be examined. This study was designed to assess how feedback, used to alter lower-extremity loading during gait, affects the structure of stride interval variability by examining long-range stride-to-stride correlations during gait in those with unilateral ACLR. Twelve participants walked under three separate loading conditions: (1) control (i.e., no cue) (2) high loading, and (3) low loading. Baseline vertical ground reaction force (vGRF) data was used to calculate a target 5% change in vGRF for the appropriate loading condition (i.e., high loading was +5% vGRF, low loading was −5% vGRF). The target for the load condition was displayed on a screen along with real-time vGRF values, prescribing changes in stride-to-stride peak vertical ground reaction forces of each limb. From time-series of stride intervals (i.e., duration), we analyzed the mean and standard deviation of stride-to-stride variability and, via detrended fluctuation analysis (i.e., DFA α), temporal persistence for each feedback condition. Both the high and low loading conditions exhibited a change toward more temporally persistent stride intervals (high loading: α =0.92, low loading: α = 0.98) than walking under the control condition (α = 0.78; high vs. control: p = .026, low vs. control: p = .001). Overall, these results indicate that altering lower extremity load changes the temporal persistence of the stride internal dynamics in ACLR individuals, demonstrating the implications of the design of gait training interventions and the influence feedback has on movement strategies.     

The impact of speed and time on gait dynamics

To determine the effects of speed on gait previous studies have examined young adults walking at different speeds; however, the small number of strides may have influenced the results. The aim of this study was to investigate the immediate and long-term impact of continuous slow walking on the mean, variability and structure of stride-to-stride measures. Fourteen young adults walked at a constant pace on a treadmill at three speeds (preferred walking speed (PWS), 90% and 80% PWS) for 30 min each. Spatiotemporal gait parameters were computed over six successive 5-min intervals. Walking slower significantly decreased stride length, while stride period and width increased. Additionally, stride period and width variability increased. Signal regularity of stride width increased and decreased in stride period. Persistence of stride period and width increased significantly at slower speeds. While several measures changed during 30 min of walking, only stride period variability and signal regularity revealed a significant speed and time interaction. Healthy young adults walking at slower than preferred speeds demonstrated greater persistence and signal regularity of stride period while spatiotemporal changes such as increased stride width and period variability arose. These results suggest that different control processes are involved in adapting to the slower speeds.     

GPS analysis of human locomotion: further evidence for long-range correlations in stride-to-stride fluctuations of gait parameters

During free walking, gait is automatically adjusted to provide optimal mechanical output and minimal energy expenditure; gait parameters, such as cadence, fluctuate from one stride to the next around average values. It was described that this fluctuation exhibited long-range correlations and fractal-like patterns. In addition, it was suggested that these long-range correlations disappeared if the participant followed the beep of metronome to regulate his or her pace. Until now, these fractal fluctuations were only observed for stride interval, because no technique existed to adequately analyze an extended time of free walking. The aim of the present study was to measure walking speed (WS), step frequency (SF) and step length (SL) with high accuracy (<1 cm) satellite positioning method (global positioning system or GPS) in order to detect long-range correlations in the stride-to-stride fluctuations. Eight participants walked 30 min under free and constrained (metronome) conditions. Under free walking conditions, DFA (detrended fluctuation analysis) and surrogate data tests showed that the fluctuation of WS, SL and SF exhibited a fractal pattern (i.e., scaling exponent alpha: 0.5 < alpha < 1) in a large majority of participants (7/8). Under constrained conditions (metronome), SF fluctuations became significantly anti-correlated (alpha < 0.5) in all participants. However, the scaling exponent of SL and WS was not modified. We conclude that, when the walking pace is controlled by an auditory signal, the feedback loop between the planned movement (at supraspinal level) and the sensory inputs induces a continual shifting of SF around the mean (persistent anti-correlation), but with no effect on the fluctuation dynamics of the other parameters (SL, WS).     

Musical pleasure beneficially alters stride and arm swing amplitude during rhythmically-cued walking in people with Parkinson's disease

Entrainment of walking to rhythmic auditory cues (e.g., metronome and/or music) improves gait in people with Parkinson's disease (PD). Studies on healthy individuals indicate that entrainment to pleasant musical rhythm can be more beneficial for gait facilitation than entrainment to isochronous rhythm, potentially as a function of emotional/motivational responses to music and their associated influence on motor function. Here, we sought to investigate how emotional attributes of music and isochronous cues influence stride and arm swing amplitude in people with PD. A within-subjects experimental trial was completed with persons with PD serving as their own controls. Twenty-three individuals with PD walked to the cue of self-chosen pleasant music cue, pitch-distorted unpleasant music, and an emotionally neutral isochronous drumbeat. All music cues were tempo-matched to individual walking pace at baseline. Greater gait velocity, stride length, arm swing peak velocity and arm swing range of motion (RoM) were found when patients walked to pleasant music cues compared to baseline, walking to unpleasant music, and walking to isochronous cues. Cued walking in general marginally increased variability of stride-to-stride time and length compared with uncued walking. Enhanced stride and arm swing amplitude were most strongly associated with increases in perceived enjoyment and pleasant musical emotions such as power, tenderness, and joyful activation. Musical pleasure contributes to improvement of stride and arm swing amplitude in people with PD, independent of perceived familiarity with music, cognitive demands of music listening, and beat salience. Our findings aid in understanding the role of musical pleasure in invigorating gait in PD, and inform novel approaches for restoring or compensating impaired motor circuits.     

Gait complexity is acutely restored in older adults when walking to a fractal-like visual stimulus

Typically, gait rehabilitation uses an invariant stimulus paradigm to improve gait related deficiencies. However, this approach may not be optimal as it does not incorporate gait complexity, or in more precise words, the variable fractal-like nature found in the gait fluctuations commonly observed in healthy populations. Aging which also affects gait complexity, resulting in a loss of adaptability to the surrounding environment, could benefit from gait rehabilitation that incorporates a variable fractal-like stimulus paradigm. Therefore, the present study aimed to investigate the effect of a variable fractal-like visual stimulus on the stride-to-stride fluctuations of older adults during overground walking. Additionally, our study aimed to investigate potential retention effects by instructing the participants to continue walking after turning off the stimulus. Older adults walked 8 min with i) no stimulus (self-paced), ii) a variable fractal-like visual stimulus and iii) an invariant visual stimulus. In the two visual stimuli conditions, the participants walked 8 additional minutes after the stimulus was turned off. Gait complexity was evaluated with the widely used fractal scaling exponent calculated through the detrended fluctuation analysis of the stride time intervals. We found a significant ~20% increase in the scaling exponent from the no stimulus to the variable fractal-like stimulus condition. However, no differences were found when the older adults walked to the invariant stimulus. The observed increase was towards the values found in the past to characterize healthy young adults. We have also observed that these positive effects were retained even when the stimulus was turned off for the fractal condition, practically, acutely restoring gait complexity of older adults. These very promising results should motivate researchers and clinicians to perform clinical trials in order to investigate the potential of visual variable fractal-like stimulus for gait rehabilitation.     

Gait and risk of falls associated with frontal cognitive functions at different stages of Alzheimer's disease

ABSTRACT The decline in frontal cognitive functions contributes to alterations of gait and increases the risk of falls in patients with dementia, a category which included Alzheimer's disease (AD). The objective of the present study was to compare the gait parameters and the risk of falls among patients at different stages of AD, and to relate these variables with cognitive functions. This is a cross-sectional study with 23 patients with mild and moderate AD. The Clinical Dementia Rating was used to classify the dementia severity. The kinematic parameters of gait (cadence, stride length, and stride speed) were analyzed under two conditions: (a) single task (free gait) and (b) dual task (walking and counting down). The risk of falls was evaluated using the Timed Up-and-Go test. The frontal cognitive functions were evaluated using the Frontal Assessment Battery (FAB), the Clock Drawing Test (CDT) and the Symbol Search Subtest. The patients who were at the moderate stage suffered reduced performance in their stride length and stride speed in the single task and had made more counting errors in the dual task and still had a higher fall risk. Both the mild and the moderate patients exhibited significant decreases in stride length, stride speed and cadence in the dual task. Was detected a significant correlation between CDT, FAB, and stride speed in the dual task condition. We also found a significant correlation between subtest Similarities, FAB and cadence in the dual task condition. The dual task produced changes in the kinematic parameters of gait for the mild and moderate AD patients and the gait alterations are related to frontal cognitive functions, particularly executive functions.     

Measures of dynamic stability: Detecting differences between walking overground and on a compliant surface

Numerous measures of dynamic stability have been proposed to gauge fall risk in the elderly, including stride interval variability and variability of the center of mass. However, these measures have been deemed inadequate because they do not take into account temporal information. Therefore, research on the measurement of dynamic stability has turned to other analysis methods such as stride interval dynamics and the maximum Lyapunov exponent. Stride interval dynamics reflect the statistical persistence of an individual’s stride interval time series and the Lyapunov exponent quantifies local dynamic stability – the sensitivity of the system to infinitesimal perturbations. In this study, we compare the ability of these measurement tools to detect changes between overground and compliant-surface walking, a condition known to affect stability, to determine their aptness as measures of dynamic stability. Fourteen able-bodied participants completed three 15 min walks, two overground and one on a compliant surface. Our results show that the Lyapunov exponent may be more sensitive to gait changes than stride interval dynamics and gait variability measures.     

Gait and risk of falls associated with frontal cognitive functions at different stages of Alzheimer's disease

ABSTRACT

The decline in frontal cognitive functions contributes to alterations of gait and increases the risk of falls in patients with dementia, a category which included Alzheimer's disease (AD). The objective of the present study was to compare the gait parameters and the risk of falls among patients at different stages of AD, and to relate these variables with cognitive functions. This is a cross-sectional study with 23 patients with mild and moderate AD. The Clinical Dementia Rating was used to classify the dementia severity. The kinematic parameters of gait (cadence, stride length, and stride speed) were analyzed under two conditions: (a) single task (free gait) and (b) dual task (walking and counting down). The risk of falls was evaluated using the Timed Up-and-Go test. The frontal cognitive functions were evaluated using the Frontal Assessment Battery (FAB), the Clock Drawing Test (CDT) and the Symbol Search Subtest. The patients who were at the moderate stage suffered reduced performance in their stride length and stride speed in the single task and had made more counting errors in the dual task and still had a higher fall risk. Both the mild and the moderate patients exhibited significant decreases in stride length, stride speed and cadence in the dual task. Was detected a significant correlation between CDT, FAB, and stride speed in the dual task condition. We also found a significant correlation between subtest Similarities, FAB and cadence in the dual task condition. The dual task produced changes in the kinematic parameters of gait for the mild and moderate AD patients and the gait alterations are related to frontal cognitive functions, particularly executive functions.     

Exploring gait adaptations to perturbed and conventional treadmill training in Parkinson’s disease: Time-course,sustainability, and transfer

BackgroundGait impairment is a major motor symptom in Parkinson’s disease (PD), and treadmill training is an effective non-pharmacological treatment option.Research questionIn this study, the time course, sustainability and transferability of gait adaptations to treadmill training with and without additional postural perturbations were investigated.Methods38 PD patients (Hoehn & Yahr 1–3.5) were randomly allocated to eight weeks of treadmill training, performed twice-weekly for 40 min either with (perturbation treadmill training [PTT], n = 18) or without (conventional treadmill training [CTT], n = 20) additional perturbations to the treadmill surface. Spatiotemporal gait parameters were assessed during treadmill walking on a weekly basis (T0–T8), and after three months follow-up (T9). Additional overground gait analyses were performed at T0 and T8 to investigate transfer effects.ResultsTreadmill gait variability reduced linearly over the course of 8 weeks in both groups (p < .001; Cohen’s d (range): −0.53 to −0.84). Only the PTT group significantly improved in other gait parameters (stride length/time, stance-/swing time), with stride time showing a significant between-group interaction effect (Cohen’s d = 0.33; p = .05). Additional between-group interactions indicated more sustained improvements in stance (Cohen’s d = 0.85; p = .02) and swing time variability in the PTT group (Cohen’s d = 0.82; p = .03) at T9. Overground gait improvements at T8 existed only in stance (d = -0.73; p = .04) and swing time (d = 0.73; p = .04).DiscussionTreadmill stride-to-stride variability reduced substantially and linearly, but transfer to overground walking was limited. Adding postural perturbations tended to increase efficacy and sustainability of several gait parameters. However, since between-group effects were small, more work is necessary to support these findings.     

Locomotor strategies in response to altered lower limb segmental mechanical properties

The present study sought to use stilt walking as a model to uncover modifications to gait dynamics caused by changes in lower limb anthropometrics. We examined 10 novice and 10 expert stilt walkers, each walking with and without stilts, to determine the specific adaptations brought about by experience. Three-dimensional kinematics and force platform data were used to calculate the intersegmental forces, net joint moments and moment powers at the ankle, knee and hip. Spatio-temporal data were computed to aid the interpretation of these data. Non-dimensional scaling was used to facilitate comparison between stilt- and normal-walking. In general, the stilts induced largely the same alterations in the locomotor patterns of both novices and experts, which did not allow for the conclusion that the experts employed locomotor dynamics that were better suited to the challenges imposed by alterations to limb length, mass and mass moment of inertia induced by the stilts. Nevertheless, the experts exhibited a lesser reduction in dimensionless stride length and velocity and generated larger concentric knee flexor and hip extensor powers, relative to the novices, which may be indicative of enhanced dynamic stability control.     

Spatial and temporal variability of movement parameters in individuals with Down syndrome

This investigation compared spatial and temporal gait movement parameters of a sample of individuals with Down syndrome (n=12) and one of individuals without disabilities (n=12). All participants were evaluated on responses to a preferred pace and fast walk with the GAITRite Electronic Walkway. Spatial outcomes included step and stride length, step and stride width, toe-in/toe-out, and base of support. Temporal outcomes included step time, velocity, single and double leg support time, stance, and swing time. There were significant group differences for step length, step width, stride length, and velocity in the preferred walk condition. Significant group differences for step length, step width, and stride length were observed in the fast walk condition. Percentage differences also indicated lower scores for all spatial and temporal variables in relation to the control group. The ability to control gait movements appears to reflect earlier movement experiences, so it may be possible to use variable sensory feedback and specific training to modify and adjust movement responses and improve gait performance in Down syndrome.     

Residual attentional capacity amongst young and elderly during dual and triple task walking

Walking is considered an automatic function which demands little attentional resources. Thus a residual attentional capacity is available for a concurrent task (dual task). Minor age-related deficits in postural control may minimize the residual attentional capacity, however this may not be detected by a simple examination of the individuals gait performance. This study investigated the use of challenging dual task combinations to detect age related changes in gait performance. Eleven community-dwelling elderly (mean age 76 years) and 13 young subjects (mean age 26 years) participated in the study. The participants walked along a figure-of-eight track at a self-selected speed. The effect of introducing a concurrent cognitive task and a concurrent functional motor task was evaluated. Stride-to-stride variability was measured by heel contacts and by trunk accelerometry. In response to the cognitive task the elderly increased their temporal stride-to-stride variability by 39% in the walking task and by 57% in the combined motor task. These increases were significantly larger than observed for the young. Equivalent decreases in trunk acceleration autocorrelation coefficients and gait speed were found. A combination of sufficiently challenging motor tasks and concurrent cognitive tasks can reveal signs of limited residual attentional capacity during walking amongst the elderly.     

Entrainment to a real time fractal visual stimulus modulates fractal gait dynamics

Fractal patterns characterize healthy biological systems and are considered to reflect the ability of the system to adapt to varying environmental conditions. Previous research has shown that fractal patterns in gait are altered following natural aging or disease, and this has potential negative consequences for gait adaptability that can lead to increased risk of injury. However, the flexibility of a healthy neurological system to exhibit different fractal patterns in gait has yet to be explored, and this is a necessary step toward understanding human locomotor control. Fifteen participants walked for 15 min on a treadmill, either in the absence of a visual stimulus or while they attempted to couple the timing of their gait with a visual metronome that exhibited a persistent fractal pattern (contained long-range correlations) or a random pattern (contained no long-range correlations). The stride-to-stride intervals of the participants were recorded via analog foot pressure switches and submitted to detrended fluctuation analysis (DFA) to determine if the fractal patterns during the visual metronome conditions differed from the baseline (no metronome) condition. DFA α in the baseline condition was 0.77 ± 0.09. The fractal patterns in the stride-to-stride intervals were significantly altered when walking to the fractal metronome (DFA α = 0.87 ± 0.06) and to the random metronome (DFA α = 0.61 ± 0.10) (both p < .05 when compared to the baseline condition), indicating that a global change in gait dynamics was observed. A variety of strategies were identified at the local level with a cross-correlation analysis, indicating that local behavior did not account for the consistent global changes. Collectively, the results show that a gait dynamics can be shifted in a prescribed manner using a visual stimulus and the shift appears to be a global phenomenon.     

Sensorimotor synchronization during gait is altered by the addition of variability to an external cue

Sensorimotor synchronization has been used in the rehabilitation of gait, yet much remains unknown regarding the optimal use of this technique. The purpose of this study was to test the hypothesis that adding small amounts of variability to the motion of a vertically oscillating treadmill would affect the behavior of healthy walkers. Sixteen young adults walked on a treadmill and pneumatically actuated platform for one control trial (no oscillation) and eight trials in which the walking surface oscillated in the vertical direction under different conditions of variability. During the oscillation trials, the mean frequency of oscillation was equal to the preferred step frequency of the participant, but each individual cycle period was allowed to vary within a pre-determined range from 0% (no variability) to ±25% (high variability) of the mean cycle period. The amount of variance of each cycle period within each condition was drawn randomly from a white noise generator. Synchronization was improved when a small amount of noise was added to the platform motion but synchronization significantly decreased at higher levels of noise. Coefficient of variation of stride duration was relatively unchanged at lower levels of variability, but increased significantly at higher levels of variability. Statistical persistence of stride duration was significantly reduced during all trials with vertical oscillation relative to normal walking, but was not significantly altered by variability in the treadmill oscillation. These results suggest that the addition of a small amount of random variability to the cycle period of an oscillator may enhance sensorimotor synchronization of gait to an external signal. These data may have implications for the use of synchronization in a therapeutic setting.     

Domestic cat walking parallels human constrained optimization: Optimization strategies and the comparison of normal and sensory deficient individuals

To evaluate how fundamental gait parameters used in walking (stride length, frequency, speed) are selected by cats we compared stride characteristics selected when walking on a solid surface to those selected when they were constrained to specific stride lengths using a pedestal walkway. Humans spontaneously select substantially different stride length–stride frequency–speed relationships in walking when each of these parameters is constrained, as in walking to a metronome beat (frequency constrained), evenly spaced floor markers (stride length constrained) or on a treadmill (speed constrained). In humans such adjustments largely provide energetic economy under the prescribed walking conditions. Cats show a similar shift in gait parameter selection between conditions as observed in humans. This suggests that cats (and by extension, quadrupedal mammals) also select gait parameters to optimize walking cost-effectiveness. Cats with a profound peripheral sensory deficit (from pyridoxine overdose) appeared to parallel the optimization seen in healthy cats, but without the same level of precision. Recent studies in humans suggest that gait optimization may proceed in two stages – a fast perception-based stage that provides the initial gait selection strategy which is then fine-tuned by feedback. The sensory deficit cats appeared unable to accomplish the feedback-dependent aspect of this process.     

The effect of dividing attention between walking and auxiliary tasks in people with Parkinson's disease

This controlled study examined the effects of dividing attention between walking and the performance of a secondary cognitive task in people with mild to moderate Parkinson's disease (Hoehn and Yahr stages 2-3.5). Participants in the training group (n=6) received 30 min divided attention training in taking big steps while simultaneously performing serial three subtractions. Participants in the control group (n=6) received no training. Stride length, gait velocity and accurate enumeration rate were measured at baseline, immediate after training and 30 min after training under single-task (walk only or subtract only) and dual-task (walk and subtract) conditions. Data were also collected at training in the training group. Immediate improvement in stride length and gait velocity was found when instruction was given to participants to pay equal attention to gait and subtractions (p=0.001, p=0.05) compared to baseline. Short-term improvement in the gait variables was also found after training when compared to the controls (p=0.001, p=0.001). Nevertheless, there was no significant difference in the accurate enumeration rate. Based on the findings, we conclude that divided attention can be used as a strategy to improve slow and short-stepped gait under dual-task conditions. Divided attention can also be used in gait training for short term stride length and gait velocity improvement.     

Speed influences on the scaling behavior of gait cycle fluctuations during treadmill running

The current study examined the temporal structure of gait cycle fluctuations in running. Participants ran at 80%, 90%, 100%, 110% and 120% of preferred running speed for 8min trials. Kinematic and kinetic gait cycle variables were generated from ground reaction force data. Mean, SD and CV of the kinematic and kinetic variables changed linearly with speed, whereas U-shaped functions were found for the scaling exponent alpha in 5 of the 8 variables investigated. Our findings reveal that long range correlations are present in both kinetic and kinematic variables of the gait cycle. The dependent structure of the stride interval is reduced at preferred running speed and this is hypothesized to be related to the enhanced stability and flexibility of this gait speed.     

An investigation of stride interval stationarity while listening to music or viewing television

In recent years, there has been considerable interest in the effects of auditory and visual distractions on pedestrian ambulation. A fundamental temporal characteristic of ambulation is the temporal fluctuation of the stride interval. In this paper, we investigate the stationarity of stride interval time series when people are exposed to different forms of auditory and visual distractions. An increase in nonstationary behavior may be suggestive of divided attention and more frequent central modulation of locomotion, both of which may have ramifications on pedestrian vigilance and responsiveness to environmental perturbations. One group of fifteen able-bodied (6 females) young adult participants completed a music protocol (overground walking with and without music). A second group of fifteen (7 females) did a television protocol (treadmill walking while watching TV with and without sound). Three walking trials, each 15min in duration, were performed at each participant's comfortable walking speed, with force sensitive resistors under the heel of each foot. Using the reverse arrangements test, the vast majority of time series were nonstationary, with a time-varying mean as the principal source of nonstationarity. Furthermore, the television trial with sound had the greatest number of nonstationarities followed by overground walking while listening to music. We discuss the possibility that these conditions measurably affect gait dynamics through a subconscious synchronization to external rhythms or a cyclic distraction followed by a period of increased conscious correction of gait timing. Our findings suggest that the regulation of stride timing is particularly susceptible to constant, time-evolving auditory stimuli, but that normal pacing can be restored quickly upon stimulus withdrawal. These kinds of sensory distractions should thus be carefully considered in studies of pedestrian ambulation.     

Relationships between dual-task related changes in stride velocity and stride time variability in healthy older adults

Dual-task related gait changes have been previously reported for healthy older adults, suggesting that gait control requires attention. Compared to balance control, the involvement of attention in the control of the rhythmic stepping mechanism, as reflected by stride time variability, is not well known. In particular, under dual-task, the relative contributions of a second, attention-demanding task and changes in walking speed remain unclear. Thus, the aims of this study were (1) to assess whether walking with a slow-selected speed or walking while performing an attention-demanding task affected stride time variability in a sample of healthy older participants, and (2) to establish whether stride time variability under dual-task conditions is related either to the decrease of walking speed or the simultaneous attention-demanding task, or to both. Forty-five healthy older participants performed four experimental conditions: (1) walking at a normal self-selected speed, (2) walking at a slow self-selected speed, (3) performing a verbal fluency task when sitting on a chair, and (4) performing the verbal fluency task while walking at self-selected walking speed. Gait parameters were recorded across 15 meters, using Physilog. Results showed a significant dual-task related decrease in mean values of stride velocity, as well as a significant increase in mean values and coefficients of variation of stride time. These dual-task related changes in stride time were explained by the simultaneous performance of the verbal fluency task, the decrease of gait speed and the variability between participants. Although a relationship exists between decreased walking speed and increased stride time variability, the dual-task related increase of stride time variability was also significantly associated with the attention-demanding task, suggesting some attentional control for the rhythmic stepping mechanism of walking in healthy older adults.     

Biomechanical motor patterns in normal walking

Motor patterns in normal human gait are evident in several biomechanical and EMG analyses over the stride period. Some of these patterns are invariant over the stride period with changes of cadence, whole others are closely correlated with speed changes. The findings for slow, natural, and fast walking are summarized: 1. Joint angle patterns over the stride period are quite invariant, and do not change with cadence; 2. Moment of force patterns at the ankle are least variable and quite consistent at all speeds; 3. A recently defined support moment is quite consistent at all speeds. 4. Moments at the knee and hip are highly variable at all cadences but decrease their variability as cadence increases; 5. Mechanical power patterns at all joints show consistent timing over the stride period; 6. EMG profiles of 5 muscles show consistent timing over the stride, but the amplitude increases as walking speed increases. Arguments are presented to support the concept that walking speed is largely controlled by gain and that the timing of the motor patterns, which is extremely tightly synchronized with the anatomical position, is under major afferent control.