Walking and running on the circular treadmill: transition speed and podokinetic aftereffects

The author compared 10 participants' self-selected walk-to-run transition speeds on a standard treadmill with those on a circular treadmill. The speed of the outer limb at walk-to-run transition on the circular treadmill and on the standard treadmill were very similar. Adaptive aftereffects from running and walking on the circular treadmill were also similar. When asked to step in place without vision, all participants inadvertently turned in circles following walking or running on the treadmill. The results of the present study suggest that the mechanisms controlling walk-to-run transitions are similar for the standard and circular treadmills and demonstrate the robust generalizability of locomotor aftereffects from running to walking. Adaptive control of speed, form, and direction may therefore share similar mechanisms for walking and running.     

Age-dependent variability in spatiotemporal gait parameters and the walk-to-run transition

Adolescents tend to exhibit more variability in their gait patterns than adults, suggesting a lack of gait maturity during this period of ongoing musculoskeletal growth and development. However, there is a lack of consensus over the age at which mature gait patterns are achieved and the factors contributing to gait maturation. Therefore, the purpose of this study was to investigate gait control and maturity in adolescents by determining if differences existed between adolescents and adults in a) the amount of spatiotemporal variability of walking and running patterns across a range of speeds, and b) how swiftly gait patterns are adapted to increasing gait speed during the walk-to-run transition. Forty-six adolescents (10–12-year-olds, n = 17; 13–14-year-olds, n = 12; and 15–17-year-olds, n = 17) and 12 young adults completed an incrementally ramped treadmill test (+0.2 km·h⁻¹ every 30 s) to determine the preferred transition speed (PTS) during a walk-to-run transition. Age-related differences in the variability of stride lengths and stride durations were assessed across 4 speeds (self-selected walking speed, PTS − 0.06 m·s⁻¹, PTS + 0.06 m·s⁻¹, PTS + 0.83 m·s⁻¹). Repeated measures ANOVAs (p < 0.05) compared coefficients of variation for these spatiotemporal parameters, while a one-way ANOVA compared the numbers of gait transitions and speed increments used to identify PTS between the adolescent groups and young adults. Compared to adults, 10–12yo exhibited more spatiotemporal variability during all gait conditions, while 13–17yo only exhibited more variability at PTS + 0.06 m·s⁻¹. No age-dependent pattern was observed in PTS values, but 10–12yo completed more gait transitions over more speed increments than 15–17yo and adults. The development of mature gait patterns is thus a progressive process, with walking maturing at an earlier age than running. As 10-12yo were unable to swiftly adapt gait patterns to the changing task demands, their control mechanisms of gait may not have fully matured yet.     

Self-motion perception during locomotor recalibration: more than meets the eye

Do locomotor aftereffects depend specifically on visual feedback? In 7 experiments, 116 college students were tested, with closed eyes, at stationary running or at walking to a previewed target after adaptation, with closed eyes, to treadmill locomotion. Subjects showed faster inadvertent drift during stationary running and increased distance (overshoot) when walking to a target. Overshoot seemed to saturate (i.e., reach a ceiling) at 17% after as little as 1 min of adaptation. Sidestepping at test reduced overshoot, suggesting motor specificity. But inadvertent drift effects were decreased if the eyes were open and the treadmill was drawn through the environment during adaptation, indicating that these effects involve self-motion perception. Differences in expression of inadvertent drift and of overshoot after adaptation to treadmill locomotion may have been due to different sets of ancillary cues available for the 2 tasks. Self-motion perception is multimodal.     

Cadence (steps/min) as an indicator of the walk-to-run transition

BackgroundHumans naturally transition from walking to running at a point known as the walk-to-run transition (WRT). The WRT commonly occurs at a speed of ∼2.1 m/s (m/s) or a Froude number (dimensionless value considering leg length) of 0.5. Emerging evidence suggests the WRT can also be classified using a cadence of 140 steps/min. An accurate cadence-based WRT metric would aid in classifying wearable technology minute-level step metrics as walking vs. running.PurposeTo evaluate performance of 1) WRT predictors directly identified from a treadmill-based dataset of sequentially faster bouts, and 2) accepted WRT predictors compiled from previous literature.MethodsTwenty-eight adults (71.4% men; age = 36.6 ± 12.8 years, BMI = 26.2 ± 4.7 kg/m²) completed a series of five-minute treadmill walking bouts increasing in 0.2 m/s increments until they freely chose to run. Optimal WRT values for speed, Froude number, and cadence were identified using receiver operating characteristic (ROC) curve analyses. WRT value performance was evaluated via classification accuracy metrics.ResultsOverall accuracies (metric, percent) according to WRT predictors from previous literature were: speed (2.1 m/s, 55.0%), Froude number (0.5, 76.8%), and cadence (140 steps/min, 91.1%), and those from the dataset herein were: speed (1.9 and 2.0 m/s, 78.6%), Froude number (0.68, 77.3%), and cadence (134, 139, and 141 steps/min, 92.9%). The three equally accurate cadence values support a heuristic range of cadence-based WRT values in young and middle-aged adults: 135–140 steps/min.SignificanceA tight range of cadence values performed better as WRT predictors compared to either previously reported or directly identified speed or Froude number values. These findings have important implications for gait classification, especially considering cadence is a simple metric which can be readily assessed across settings using direct observation or wearable technologies.     

Human walk-to-run transition in the context of the behaviour of complex systems

This study had two main aims: 1) to investigate if the walk-to-run (WR-) transition occurs when the speed of locomotion is kept constant below the WR-transition speed (speed clamp) and the stride rate is increased monotonously using a metronome and 2) to investigate if diversion of attention and awareness from the locomotion process influences the position of the WR-transition in stride rate, stride length, and locomotion speed (SrSlLs) space.Eighteen healthy individuals (13 men and 5 women) were recruited (age: 23.9 ± 1.5 years, height: 1.77 ± 0.10 m and body mass: 77.3 ± 12.8 kg). Stride-by-stride stride rates, stride lengths, locomotion speeds, and duty factors were determined on a treadmill in 4 different tests: 1) reference WR-transition, 2) preferred walking speed, 3) dual-task test including arithmetic calculations and 4) four speed clamp bouts with different initial velocities.Walk-to-run transitions were elicited in all participants in the speed clamp bouts. When the stride rate ramp was clamped at preferred walking speed the WR-transition stride rate was not significantly different from the WR-transition stride rate during the reference test (t = 2.2, p = 0.312). However, in the SrSlLs space the speed clamp WR-transitions all deviated from the position of the reference WR-transition. Additionally, it was demonstrated that intensive attentional diversion using a dual-task paradigm had very little influence on the position of the WR-transition in the SrSlLs space.It is argued that these observations can be explained in the context of the behavior of complex systems.     

Effects of visual focus and gait speed on walking balance in the frontal plane

We investigated how head position and gait speed influenced frontal plane balance responses to external perturbations during gait. Thirteen healthy participants walked on a treadmill at three different gait speeds. Visual conditions included either focus downward on lower extremities and walking surface only or focus forward on a stationary scene with horizontal and vertical lines. The treadmill was positioned on a platform that was stationary (non-perturbed) or moving in a pattern that appeared random to the subjects (perturbed). In non-perturbed walking, medial–lateral upper body motion was very similar between visual conditions. However, in perturbed walking, there was significantly less body motion when focus was on the stationary visual scene, suggesting visual feedback of stationary vertical and horizontal cues are particularly important when balance is challenged. Sensitivity of body motion to perturbations was significantly decreased by increasing gait speed, suggesting that faster walking was less sensitive to frontal plane perturbations. Finally, our use of external perturbations supported the idea that certain differences in balance control mechanisms can only be detected in more challenging situations, which is an important consideration for approaches to investigating sensory contribution to balance during gait.     

Evidence for generalized motor programs using gait pattern analysis

Human intra limb gait kinematics were analyzed via statistical and structural pattern recognition methods to determine the role of relative timing of limb segments within and between modes of gait. Five experienced runners were filmed while walking (3-6 km/hour) and running (8-12 km/hour) on a motor driven treadmill. Kinematic data consisted of relative timing of the four phases of the Philippson step cycle and intersegmental limb trajectories, determined from angle-angle diagrams. Despite marked decreases in absolute time durations within gaits remained constant over the speeds which were studied. Although a 2-fold increase in locomotor speed occurred in walking and a 1.5-fold speed increase occurred within running, the percentage of time spent in each of the Philippson phases was not significantly changed. However, significant differences in the time percentages and sequences of the step cycle phases were found between walking and running. Correlations between limb segment trajectories occurring in the different gaits showed strong coherence for overall step cycle patterns, but within step cycle phases and across speeds, selective phases displayed little correspondence.     

Gait transitions are not dependent on changes in intralimb coordination variability

The HKB model (H. Haken, J. A. S. Kelso, & H. Bunz, 1985) of coordination has been predominantly applied to upper extremity stationary movements. It predicts increased variability of relative phase before a transition and a decrease after a transition. The authors of the present study extended the intralimb lower extremity locomotive research of F. J. Diedrich and W. H. Warren (1995) by conducting continuous treadmill walk-to-run and run-to-walk trials with 10 participants. Standard deviation of knee-ankle and hip-ankle relative phase did not increase before walk-to-run and run-to-walk transitions, and there was no decrease in knee-ankle relative phase variability after either transition. The results of this study did not provide strong support for application of the variability predictions of the HKB model of coordination to lower extremity intralimb coordination during gait transitions.     

Gait symmetric adaptation: Comparing effects of implicit visual distortion versus split-belt treadmill on aftereffects of adapted step length symmetry

Understanding gait adaptation is essential for rehabilitation, and visual feedback can be used during gait rehabilitation to develop effective gait training. We have previously shown that subjects can adapt spatial aspects of walking to an implicitly imposed distortion of visual feedback of step length. To further investigate the storage benefit of an implicit process engaged in visual feedback distortion, we compared the robustness of aftereffects acquired by visual feedback distortion, versus split-belt treadmill walking. For the visual distortion trial, we implicitly distorted the visual representation of subjects’ gait symmetry, whereas for the split-belt trial, the speed ratio of the two belts was gradually adjusted without visual feedback. After adaptation, the visual feedback or the split-belt perturbation was removed while subjects continued walking, and aftereffects of preserved asymmetric pattern were assessed. We found that subjects trained with visual distortion trial retained aftereffects longest. In response to the larger speed ratio of split-belt walking, the subjects showed an increase in the size of aftereffects compared to the smaller speed ratio, but it steeply decreased over time in all the speed ratios tested. In contrast, the visual distortion group showed much slower decreasing rate of aftereffects, which was evidence of longer storage of an adapted gait pattern. Visual distortion adaptation may involve the interaction and integration of the change in motor strategy and implicit process in sensorimotor adaptation. Although it should be clarified more clearly through further studies, the findings of this study suggest that gait control employs distinct adaptive processes during the visual distortion and split-belt walking and also the level of reliance of an implicit process may be greater in the visual distortion adaptation than the split-belt walking adaptation.     

Not letting the left leg know what the right leg is doing: limb-specific locomotor adaptation to sensory-cue conflict

We investigated the phenomenon of limb-specific locomotor adaptation in order to adjudicate between sensory-cue-conflict theory and motor-adaptation theory. The results were consistent with cue-conflict theory in demonstrating that two different leg-specific hopping aftereffects are modulated by the presence of conflicting estimates of self-motion from visual and nonvisual sources. Experiment 1 shows that leg-specific increases in forward drift during attempts to hop in place on one leg while blindfolded vary according to the relationship between visual information and motor activity during an adaptation to outdoor forward hopping. Experiment 2 shows that leg-specific changes in performance on a blindfolded hopping-to-target task are similarly modulated by the presence of cue conflict during adaptation to hopping on a treadmill. Experiment 3 shows that leg-specific aftereffects from hopping additionally produce inadvertent turning during running in place while blindfolded. The results of these experiments suggest that these leg-specific locomotor aftereffects are produced by sensory-cue conflict rather than simple motor adaptation.     

What factors determine the preferred gait transition speed in humans? A review of the triggering mechanisms

Human locomotion is a fundamental skill that is required for daily living, yet it is not completely known how human gait is regulated in a manner that seems so effortless. Gait transitions have been analyzed to gain insight into the control mechanisms of human locomotion since there is a known change that occurs as the speed of locomotion changes. Specifically, as gait speed changes, there is a spontaneous transition between walking and running that occurs at a particular speed. Despite the growing body of research on the determinants of this preferred transition speed and thus the triggering mechanisms of human gait transitions, a clear consensus regarding the control mechanisms of gait is still lacking. Therefore, this article reviews the determinants of the preferred transition speed using concepts of the dynamic systems theory and how these determinants contribute to four proposed triggers (i.e. metabolic efficiency, mechanical efficiency, mechanical load and cognitive and perceptual) of human gait transitions. While individual anthropometric and strength characteristics influence the preferred transition speed, they do not act to trigger a gait transition. The research has more strongly supported the mechanical efficiency and mechanical load determinants as triggering mechanisms of human gait transitions. These mechanical determinants, combined with cognitive and perceptual processes may thus be used to regulate human gait patterns through proprioceptive and perceptual feedback as the speed of locomotion changes.     

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.     

Gaze direction affects walking speed when using a self-paced treadmill with a virtual reality environment

BackgroundIn a previous study it was observed that participants increase their walking speed during a dual task while walking on a self-paced treadmill in a virtual reality (VR) environment (Gait Real time Analysis Interactive Lab (GRAIL)). This observation is in contrast with the limited resources hypothesis, which suggests walking speed of healthy persons to decrease when performing a cognitive dual task.AimThe aim of the present study was therefore to determine whether the cognitive demand of the task, an aroused feeling, discrepancy in optic flow or a change in gaze direction caused participants to walk faster in this computer assisted rehabilitation environment.MaterialsThe GRAIL included a self-paced treadmill, a motion-capture system and synchronized VR environments.MethodsThirteen healthy young adults (mean age 21.6 ± 2.5) were included in this study. Participants walked on the self-paced treadmill while seven different intervention conditions (IC) were offered. Prior to each IC, a control condition (CC) was used to determine the natural self-selected walking speed. Walking speed during the last 30 s of each IC was compared with the walking speed during the last 30 s of the preceding CC.ResultsResults show that the height on which a visual task was presented in the VR environment, influenced walking speed. Participants walked faster when gaze was directed above the focus of expansion.SignificanceThese findings contribute to a further understanding of the differences between walking in a real life environment or computer assisted rehabilitation environment. When analyzing gait on a self-paced treadmill in the future, one must be attentive where to place a visual stimulus in the VR environment.     

Bodyweight support alters the relationship between preferred walking speed and cost of transport

Humans tend to select a preferred walking speed (PWS) that minimizes the metabolic energy consumed per distance traveled, i.e. the Cost of Transport (CoT). The aims of this study were to: 1. compare PWS overground vs. on a treadmill at 100 and 50% of body weight, and 2. explore whether with body weight support, PWS corresponds to the speed that minimizes CoT. Fifteen healthy adults walked overground and on a lower body positive pressure treadmill with and without bodyweight support. Walking speeds (m^.s⁻¹) were recorded for each condition. Rate of energy expenditure (J^.kg^−1.min⁻¹) and CoT (J^.kg^−1.m⁻¹) were then determined from 5-min walking trials with 50% bodyweight support at PWS and ± 30% of the self-selected walking speed for that condition. PWS did not differ across conditions. With 50% body weight support, for each 30% increase in walking speed, rates of metabolic energy expenditure increased ∼15% while CoT decreased by ∼14%. Thus, with 50% body weight support, PWS did not correspond with the speed that minimized CoT. Bodyweight support decreases cost of maintaining an upright body but does not decrease the metabolic demand of limb advancement, contributing to the linear yet not proportional changes in rates of energy expenditure and CoT. We conclude that bodyweight support via an AlterG® treadmill disconnects the association between PWS and minimum CoT. These findings have implications for clinical populations (e.g., obese, elderly) who may benefit from walking on a bodyweight supporting treadmill but may select speeds incompatible with their physical activity goals.     

Are transitions in human gait determined by mechanical,kinetic or energetic factors?

It is currently unclear whether it is the need to maintain metabolic efficiency, the need to keep skeletal loading below critical force levels, or simple mechanical factors that drive the walk-to-run (W-R) and run-to-walk (R-W) transitions in human gait. Eighteen adults (9 males and 9 females) locomoted on an instrumented treadmill using their preferred gait. Each completed 2 ascending (W-R) and 2 descending (R-W) series of trials under three levels of loading (0%, 15% and 30% body weight). For each trial, participants locomoted for 60 s at each of 9 different speeds--4 speeds both above and below their preferred transition speed (PTS) plus their PTS. Evidence was sought for critical levels of key kinetic (maximum vertical force, impulse, first peak force, time to first peak force and maximum loading rate), energetic (oxygen consumption, transport cost) and mechanical variables (limb lengths, strength) predictive of the gait transition. Analyses suggested the kinetic variables of time to first peak force and loading rate as the most likely determinants of the W-R and R-W transitions.     

Familiarization to treadmill running in young unimpaired adults

This study investigated the time needed for familiarization to treadmill running. Seventeen young healthy adults, who were inexperienced on a treadmill, ran for 11 min on a treadmill at their self-selected speed. Discrete sagittal-plane angular kinematic parameters of the pelvis, hip, knee and ankle, and cadence and stride time data were captured with a three-dimensional motion analysis system at 0, 2, 4, 6, 8 and 10 min. Participants were considered familiarized to treadmill running by 6 min, as there were no significant changes in any dependent variables from this time. Furthermore, mean absolute difference scores between consecutive times were minimal (1.3 degrees ) and the average intraclass correlation coefficient [ICC(2,1)=.95] was maximal and highly reliable by this time. Future studies comparing treadmill and overground running need to provide an adequate treadmill familiarization time of at least 6 min prior to data capture of sagittal-plane kinematic events.     

Talking about walking: biomechanics and the language of locomotion

What drives humans around the world to converge in certain ways in their naming while diverging dramatically in others? We studied how naming patterns are constrained by investigating whether labeling of human locomotion reflects the biomechanical discontinuity between walking and running gaits. Similarity judgments of a student locomoting on a treadmill at different slopes and speeds revealed perception of this discontinuity. Naming judgments of the same clips by speakers of English, Japanese, Spanish, and Dutch showed lexical distinctions between walking and running consistent with the perceived discontinuity. Typicality judgments showed that major gait terms of the four languages share goodness-of-example gradients. These data demonstrate that naming reflects the biomechanical discontinuity between walking and running and that shared elements of naming can arise from correlations among stimulus properties that are dynamic and fleeting. The results support the proposal that converging naming patterns reflect structure in the world, not only acts of construction by observers.     

Can the Transition To and From Running and the Metabolic Cost of Running Be Determined From the Kinetic Energy of Running?

An experiment was conducted in which volume of used oxygen per stride time and the total segmental changes in kinetic energy generated per stride time, &grD;E(k)>s(-1), of 11 participants were determined on Day 1 for 7 treadmill running speeds. Gait transition speeds were determined on Day 2. Running metabolism and transition speed were predicted from the Day 1 mechanics of running expressed in Speed x &grD;E(k)>s(-1) coordinates. Predictions followed from the relation between 2 generalized quality ratios Q(metab), and Q(mech), with numerator &grD;E(k)>s(-1). In Q(metab), the denominator was the volume of used oxygen per stride time; in Q(mech), the denominator was the absolute regression constant from the linear dependency of &grD;E(k)>s(-1) on speed.     

Stability and variability may respond differently to changes in walking speed

In gait research it has often been assumed that variability and stability are negatively correlated, where increases in variability are assumed to equate with increases in instability. The purpose of this paper is to illustrate that variability does not always equate with stability. To proof this point, a method was developed to directly assess stability and variability during the application of a visual perturbation at different walking speeds. Walking variability was measured by using the average standard deviation of the knee joint angle across the gait cycle. Walking stability was measured by the recovery time of the knee joint angle trajectory from the distortion induced by a visual perturbation that was delivered at the beginning of the stance phase. Five participants were required to walk at six different velocities on a treadmill (0.67, 0.80, 0.94, 1.07, 1.21, and 1.34 m/s). The coefficients of intraclass correlations for the experiment were 83% and 80% for the calculated stability and variability, respectively. The calculated stabilities were not sensitive to changes in walking speed (p>0.98). The calculated variability however decreased with increases in walking speed (p=0.004). No significant correlation between variability and stability was observed (r=-0.002). We suggest that gait stability is independent of variability during locomotion and should thus be measured independently.     

A treadmill and motion coupled virtual reality system for gait training post-stroke.

A virtual reality (VR)-based locomotor training system has been developed for gait rehabilitation post-stroke. The system consists of a self-paced treadmill mounted onto a 6-degrees-of-freedom motion platform. Virtual environments (VEs) that are synchronized with the speed of the treadmill and the motions of the platform are rear-projected onto a screen in front of the walking subject. A feasibility study was conducted to test the capability of two stroke patients and one healthy control to be trained with the system. Three VE scenarios (corridor walking, street crossing, and park stroll) were woven into a gait-training program that provided three levels of complexity (walking speed, slopes, collision avoidances), progression criteria (number of successful trials) and knowledge of results. Results show that, with practice, patients can effectively increase their gait speed as demanded by the task and adapt their gait with respect to the change in physical terrain. However, successful completion of tasks requiring adaptation to increasing demands related to speed and physical terrains does not necessarily predict the patient's ability to anticipate and avoid collision with obstacles during walking. This feasibility study demonstrates that persons with stroke are able to adapt to this novel VR system and be immersed in the VEs for gait training.