Effects of Visually Augmented Gait Training on Foot-Ground Clearance: An Intervention to Reduce Tripping-Related Falls.

Minimum toe clearance (MTC ∼10-30 mm) is a hazardous mid-swing gait event, characterized by high-foot velocity (∼4.60 m·s-1) and single-foot support. This experiment tested treadmill-based gait training effects on MTC. Participants were 10 young (4 males and 6 females) and 10 older (6 males and 4 females) healthy ambulant individuals. The mean age, stature, and body mass for the younger group was 23 (2) years, 1.72 (0.10) m, and 67.5 (8.3) kg, and for older adults was 77 (9) years, 1.64 (0.10) m, and 71.1 (12.2) kg. Ten minutes of preferred speed treadmill walking (baseline) was followed by 20 minutes with MTC information (feedback) and 10 minutes without feedback (retention). There were no aging effects on MTC in baseline or feedback. The MTC in baseline for older adults was 14.2 (3.5) mm and feedback 27.5 (8.7) mm, and for the younger group, baseline was 12.7 (2.6) mm and feedback 28.8 (5.1) mm, respectively. Retention MTC was significantly higher for both groups, indicating a positive effect of augmented information: younger 40.8 (7.3) mm and older 27.7 (13.6) mm. Retention joint angles relative to baseline indicated that the young modulated joint angles control MTC differently using increased ankle dorsiflexion at toe off and modulating knee and hip angles later in swing closer to MTC.

Effects of walking-induced fatigue on gait function and tripping risks in older adults.

BACKGROUND: Fatigue and ageing contribute to impaired control of walking and are linked to falls. In this project, fatigue was induced by maximum speed walking to examine fatigue effects on lower limb trajectory control and associated tripping risk and overall gait functions of older adults. METHODS: Eleven young (18-35 years) and eleven older adults (>65 years) conducted 5-minute preferred speed treadmill walking prior to and following 6-minute maximum fast walking. Spatio-temporal gait parameters and minimum foot clearance (MFC) were obtained. Maximal muscle strength (hamstrings and quadriceps) was measured on an isokinetic dynamometer. Heart rate (HR) and rating of perceived exertion (RPE) assessed physiological effort and subjective fatigue. Physiological Cost Index computed walking efficiency. RESULTS: Fatigue due to fast walking increased step length, double support time and variability of step width. Only older adults reduced MFC due to fatigue. A trend of longer double support with greater MFC was found in the non-dominant limb. Lower walking efficiency was characterised as the ageing effect. Older adults did not increase HR during fast walking but higher RPE scores were observed. CONCLUSIONS: Older adults can increase tripping risk by 6 minutes of fast walking possibly by both impaired walking efficiency based on cardiac capacity and higher perceived fatigue due to elevated caution level. Regardless of age, increased step width variability due to fatigue was observed, a sign of impaired balance. Longer double support and greater MFC observed in the older adults' non-dominant limb could be an asymmetrical gait adaptation for safety.

A comparison of treadmill and overground walking effects on step cycle asymmetry in young and older individuals.

Although lower limb strength becomes asymmetrical with age, past studies of aging effects on gait biomechanics have usually analyzed only one limb. This experiment measured how aging and treadmill surface influenced both dominant and nondominant step parameters in older (mean 74.0 y) and young participants (mean 21.9 y). Step-cycle parameters were obtained from 3-dimensional position/time data during preferred-speed walking for 40 trials along a 10 m walkway and for 10 minutes of treadmill walking. Walking speed (young 1.23 m/s, older 1.24 m/s) and step velocity for the two age groups were similar in overground walking but older adults showed significantly slower walking speed (young 1.26 m/s, older 1.05 m/s) and step velocity on the treadmill due to reduced step length and prolonged step time. Older adults had shorter step length than young adults and both groups reduced step length on the treadmill. Step velocity and length of older adults' dominant limb was asymmetrically larger. Older adults increased the proportion of double support in step time when treadmill walking. This adaptation combined with reduced step velocity and length may preserve balance. The results suggest that bilateral analyses should be employed to accurately describe asymmetric features of gait especially for older adults.

Biomechanical Correlates of Falls Risk in Gait Impaired Stroke Survivors.

Increased falls risk is prevalent among stroke survivors with gait impairments. Tripping is the leading cause of falls and it is highly associated with mid-swing Minimum Foot Clearance (MFC), when the foot's vertical margin from the walking surface is minimal. The current study investigated MFC characteristics of post-stroke individuals (n = 40) and healthy senior controls (n = 21) during preferred speed treadmill walking, using an Optotrak 3D motion capture system to record foot-ground clearance. In addition to MFC, bi-lateral spatio-temporal gait parameters, including step length, step width and double support time, were obtained for the post-stroke group's Unaffected and Affected limb and the control group's Dominant and Non-dominant limbs. Statistical analysis of MFC included central tendency (mean, median), step-to-step variability (standard deviation and interquartile range) and distribution (skewness and kurtosis). In addition, the first percentile, that is the lowest 1% of MFC values (MFC 1%) were computed to identify very high-risk foot trajectory control. Spatio-temporal parameters were described using the mean and standard deviation with a 2 × 2 (Group × Limb) Multivariate Analysis of Variance applied to determine significant Group and Limb effects. Pearson's correlations were used to reveal any interdependence between gait variables and MFC control. The main finding of the current research was that post-stroke group's affected limb demonstrated lower MFC 1% with higher variability and lower kurtosis. Post-stroke gait was also characterised by shorter step length, larger step width and increased double support time. Gait retraining methods, such as using real-time biofeedback, would, therefore, be recommended for post-stroke individuals, allowing them to acquire optimum swing foot control and reduce their tripping risk by elevating the swing foot and improving step-to-step consistency in gait control.

Variability in the foot-ground clearance and step timing of young and older men during single-task and dual-task treadmill walking.

The study's aim was to document ageing effects on gait control by analysing the distributions of both left and right step timing and minimum foot-ground clearance (MFC) in older men (mean 71.1 years) and gender-matched controls (mean 26.3 years). Step durations and MFC were obtained from continuously sampled 3D markers during preferred-speed treadmill walking (single task) for 15 min and a dual-task condition in which participants walked at the same speed and also responded to the same 90 quasi-randomly presented visual reaction time (RT) stimuli. Significantly longer mean and median RTs were observed when treadmill walking compared to the standing-only control condition. Older males had significantly slower mean RTs for the standing and walking tasks (292 ms and 315 ms, respectively) than the younger group (265 ms and 273 ms). Older males walked more slowly, both groups had greater dual-task step durations but the effect was more pronounced in the older group. Older men's step durations were more positively skewed (longer) while the young had more negative skew. MFC was greater in the older group, and, importantly, in both groups right MFC was greater than the left foot. The data provide evidence of right-left limb asymmetry in preferred speed treadmill walking and it was hypothesised that behavioural slowing in locomotion could be a response to increase the safety of limb end-point control.

Balance during obstacle crossing following stroke.

Difficulty negotiating obstacles may contribute to the high falls rate following stroke. This study examined the impact of stroke on balance during obstacle crossing. Centre of mass (COM) and centre of pressure (COP) were measured as 12 stroke subjects and 12 unimpaired subjects stepped over a 4 cm high obstacle at self-selected speed. Unimpaired subjects also walked at speeds matched to their yoked stroke subject. Compared with unimpaired subjects at matched speed, at unaffected lead toe clearance, anterior-posterior (AP) separation between COM and COP increased in stroke subjects, which might indicate instability. Step lengths before and after the obstacle tended to be reduced which could increase the risk of losing balance forwards. The COM AP velocity was reduced at affected lead toe off following stroke, which may minimise instability. Following stroke the COM and COP were positioned more posteriorly during affected lead toe clearance, which might also assist stability.

Learning to minimize energy costs and maximize mechanical work in a bimanual coordination task.

The authors addressed the hypothesis that economy in motor coordination is a learning phenomenon realized by both reduced energy cost for a given workload and more external work at the same prepractice metabolic and attentional energy expenditure. "Self-optimization" of movement parameters has been proposed to reflect learned motor adaptations that minimize energy costs. Twelve men aged 22.3 -/+ 3.9 years practiced a 90 degrees relative phase, upper limb, independent ergometer cycling task at 60 rpm, followed by a transfer test of unpracticed (45 and 75 rpm) and self-paced cadences. Performance in all conditions was initially unstable, inaccurate, and relatively high in both metabolic and attentional energy costs. With practice, coordinative stability increased, more work was performed for the same metabolic and attentional costs, and the same work was done at a reduced energy cost. Self-paced cycling was initially below the metabolically optimal, but following practice at 60 rpm was closer to optimal cadence. Given the many behavioral options of the motor system in meeting a variety of everyday movement task goals, optimal metabolic and attentional energy criteria may provide a solution to the problem of selecting the most adaptive coordination and control parameters.

Tone Entropy Analysis of Augmented Information Effects on Toe-Ground Clearance When Walking.

Minimum toe clearance (MTC) is an event approximately mid-swing in the walking cycle that is critical for preventing unintended foot contact with surface irregularities ("tripping"). Treadmill-based gait training for older adults was undertaken using real-time augmented information to increase foot-ground clearance at MTC (MTC height). Ten young (Y) (Age: 23±2 year) and ten older (O) (Age: 76±9 year) participants undertook 10 min preferred speed treadmill walking (baseline) followed by 20 min with MTC height information (training) and 10 min without augmented information (retention). Three-dimensional lower limb position was sampled at 100 Hz from which MTC height was computed for each step cycle. MTC height data were analyzed using traditional descriptive statistics (mean and SD) and by computing tone (T) and entropy (E) to show, respectively, cycle-to-cycle changes to MTC height and the informational content of the MTC height time-series. There were significant ( ) age-group differences in T-E values of MTC height; Baseline ( Older=-5.40±2.00 (T); 6.63±0.23 (E); Young = -3.00±0.89 (T); 6.20±0.51 (E)), Training ( Older=-5.05±3.45 (T); 6.46±0.42 (E); Young = -2.55±0.67 (T); 6.75±0.39 (E)) Retention ( Older=-3.77±2.59 (T); 6.38±0.46 (E); Young = -2.55±0.67 (T); 6.26±0.39 (E)). Relative to baseline, tone value was significantly ( ) reduced and entropy was elevated in training and vice versa in retention phase for the young group but no significant trends were observed for older group. T and E measures of MTC height considered separately discriminated the age groups only in baseline but distinctive "clusters" were observed in tone versus entropy plots indicating characteristically different patterns of MTC adjustment over step cycles. Treadmill training with MTC height augmented information is a practical intervention for reducing tripping in older people and others with gait impairments. T-E analysis is useful for identifying characteristics of lower limb control with ageing that have not been previously recognized in studies employing traditional statistical analysis of the MTC event.

Aging effects on the metabolic and cognitive energy cost of interlimb coordination.

Many everyday motor tasks have high metabolic energy demands, and some require extended practice to learn the required coordination between limbs. Eight older (73.1 +/- 4.4 years) and 8 younger (23.3 +/- 5.9) men practiced a high-energy two-hand coordination task with both 180 degrees and 90 degrees target relative phase. The older group showed greater performance error in both conditions, and performance at 90 degrees was strongly attracted to antiphase coordination (180 degrees). In a retention test one week following the acquisition trials, the older group had learned the 180 degrees condition but did not learn the 90 degrees condition. Metabolic energy cost was not different between groups, but the older men showed higher heart rate and both conditions imposed greater cognitive demands as revealed in auditory probe reaction time. Older adults' motor learning may be inhibited by elevated heart rate at the same oxygen cost, increased cognitive cost, and an attraction toward more established low-energy in-phase or antiphase coordination.

Control of lead and trail limbs during obstacle crossing following stroke.

BACKGROUND AND PURPOSE: Obstacle crossing is compromised following stroke. The purpose of this study was to quantify modifications during obstacle clearance following stroke. SUBJECTS: Twelve subjects with stroke and 12 subjects without stroke participated in the study. METHODS: Kinematic variables were measured while participants crossed a 4-cm-high obstacle. Subjects with stroke walked at a self-selected speed; subjects without stroke walked at a comparable speed and at a self-selected speed. RESULTS: Several modifications were observed following stroke with both groups walking at self-selected speeds. The affected lead limb was positioned closer to the obstacle before crossing. Affected trail-limb clearance over the obstacle was reduced. Both affected and unaffected lead and trail limbs landed closer to the obstacle after clearance. Swing time was increased in the affected lead limb after obstacle clearance. Fewer modifications were detected at matched walking speed; the trail limb still landed closer to the obstacle. DISCUSSION AND CONCLUSION: Modifications during obstacle crossing following stroke may be partly related to walking speed. The findings raise issues of safety because people with stroke demonstrated reduced clearance of a 4-cm obstacle and limb placement closer to the obstacle after clearance.

The relationship between lower body strength and obstructed gait in community-dwelling older adults.

OBJECTIVES: To determine the relationship between lower body strength of community-dwelling older adults and the time to negotiate obstructed gait tasks. DESIGN: A correlational study. SETTING: The Biomechanics Laboratory, Deakin University, Australia. PARTICIPANTS: Twenty-nine women and 16 men aged 62 to 88 were recruited using advertisements placed in local newspapers. The participants were independent community dwellers, healthy and functionally mobile. MEASUREMENTS: Maximal isometric strength of the knee extensors and dynamic strength of the hip extensors, hip flexors, hip adductors, hip abductors, knee extensors, knee flexors, and ankle plantar flexors were assessed. The times to negotiate four obstructed gait tasks at three progressively challenging levels on an obstacle course and to complete the course were recorded. The relationship between strength and the crossing times was explored using linear regression models. RESULTS: Significant associations between the seven strength measures and the times to negotiate each gait task and to walk the entire course at each level were obtained (r = -0.38 to -0.55; P < .05). In addition, the percentage of the variance explained by strength (R(2)), consistently increased as a function of the progressively challenging level. This increase was particularly marked for the stepping over task (R(2) = 19.3%, 25.0%, and 27.2%, for levels 1, 2, and 3, respectively) and the raised surface condition (R2 = 17.1%, 21.1%, and 30.8%, for levels 1, 2, and 3, respectively). CONCLUSION: The findings of the study showed that strength is a critical requirement for obstructed locomotion. That the magnitude of the association increased as a function of the challenging levels suggests that intervention programs aimed at improving strength would potentially be effective in helping community-dwelling older adults negotiate environmental gait challenges.

The effects of improved strength on obstacle negotiation in community-living older adults.

Poor mobility has been associated with age-related deterioration in muscle strength. While previous work has examined the effects of improved strength on level walking, we have quantified the effects of a resistance-training program on obstructed gait tasks using biomechanical-dependent measures. Forty-five community-dwelling participants aged 62 years or older were randomised to either a control (n=16) or experimental group (n=29). The experimental subjects exercised for 24 weeks on a progressive resistance-training program designed to improve lower body strength. Dynamic strength was assessed at weeks 0 and 24 as well as specific laboratory gait kinetics and kinematics during stepping over an obstacle and negotiation of a raised surface set at 10, 20 and 30% of each subject's leg length. Significant strength improvements (P<0.05), ranging between 197 and 285%, were recorded in the experimental group. The strength gains in the experimental group were accompanied by significant increases in obstacle-crossing stride velocity (range 5.5-15.5%) due to increases in stride length and decreases in stride duration for both gait tasks. Significant changes in the peak vertical and anterior-posterior ground reaction forces as well as in kinematic variables associated with a safe obstacle traverse such as vertical obstacle heel clearance, limb flexion at obstacle crossing, horizontal foot placement and vertical landing velocity resulted in an improved crossing strategy in the experimental subjects. These findings provide evidence of significant improvements in obstructed gait function of community-living older adults associated with a systematic resistance-training program.

Ageing and limb dominance effects on foot-ground clearance during treadmill and overground walking.

BACKGROUND: Foot-ground clearance during the gait cycle swing phase is a critical locomotor adaptation to uneven terrain and non-optimal lower limb control has been linked to tripping and falling. The aim of this research was to determine ageing effects on bilateral foot-ground clearance during overground and treadmill walking. METHODS: Ageing and walking surface effects on bilateral foot trajectory control were investigated in 11 older (mean age 73.8 years) and 11 young (mean age 22.5 years) participants. First maximum clearance after toe-off, minimum foot-ground clearance and second maximum clearance prior to heel contact were determined from sampled 3-dimensional marker coordinates during preferred-speed treadmill walking and walking overground. FINDINGS: Preferred walking speed was lower in treadmill walking for both groups. In both groups non-dominant minimum foot-ground clearance and first maximum clearance were greater than for the dominant foot. A high positive correlation was found between these two swing foot clearances when older adults walked on the treadmill. Second maximum clearance was reduced in the older group but this was the only overall age effect. Treadmill walking reduced minimum foot-ground clearance relative to overground locomotion except in the older adults' non-dominant limb that revealed greater vertical clearance height in the non-dominant foot. INTERPRETATION: Decreased second maximum clearance in the older group may be linked to reduced dorsiflexion. Greater minimum foot-ground clearance in the older adults' non-dominant foot may reflect functional asymmetry, in which the non-dominant limb primarily secures or stabilizes gait. The high positive correlation between first maximum and minimum foot-ground clearances suggests that intervention designed to increase first maximum clearance may also increase minimum foot-ground clearance. A direction for future research is to further understand ageing effects on lower limb trajectory variables in response to a range of walking surface characteristics.

Aging effects on visual reaction time in a single task condition and when treadmill walking.

Visual reaction time (RT) was measured in 10 older men (mean age, 71.1 years) and gender-matched controls (mean age, 26.3 years) when standing (single task) and when walking on a motor-driven treadmill (dual task). There were 90 quasi-randomly presented trials over 15 min in each condition. Longer mean and median RTs were observed in the dual task compared to the single task. Older males had significantly slower mean and median RTs (315 and 304 ms, respectively) than the younger group (273 and 266 ms, respectively) in both task conditions. There were no age or condition effects on within-subject variability. Both groups showed a trend of increasing RT over the 90 single task trials but when walking only the younger group slowed. These novel findings demonstrate high but sustained attention by older adults when walking. It is proposed that the motor task's attentional demands might contribute to their slower preferred walking speed.

Visual perception of movement kinematics and the acquisition of "action prototypes".

Recognizing a class of movements as belonging to a "nominal" action category, such as walking, running, or throwing, is a fundamental human ability. Three experiments were undertaken to test the hypothesis that common ("prototypical") features of moving displays could be learned by observation. Participants viewed moving stick-figure displays resembling forearm flexion movements in the sagittal plane. Four displays (presentation displays) were first presented in which one or more movement dimensions were combined with 2 respective cues: direction (up, down), speed (fast, slow), and extent (long, short). Eight test displays were then shown, and the observer indicated whether each test display was like or unlike those previously seen. The results showed that without corrective feedback, a single cue (e.g., up or down) could be correctly recognized, on average, with the proportion correct between .66 and .87. When two cues were manipulated (e.g., up and slow), recognition accuracy remained high, ranging between .72 and .89. Three-cue displays were also easily identified. These results provide the first empirical demonstration of action-prototype learning for categories of human action and show how apparently complex kinematic patterns can be categorized in terms of common features or cues. It was also shown that probability of correct recognition of kinematic properties was reduced when the set of 4 presentation displays were more variable with respect to their shared kinematic property, such as speed or amplitude. Finally, while not conclusive, the results (from 2 of the 3 experiments) did suggest that similarity (or "likeness") with respect to a common kinematic property (or properties) is more easily recognized than dissimilarity.