Faster walking speeds increase local instability among people with peripheral neuropathy

Causal interactions and dynamic stability between limbs while walking with imposed leg constraints

Aim

To investigate the dynamics of the motor control system during walking by examining the complexity, stability, and causal relationships of leg motions. Specifically, the study focuses on gait under both bilateral and unilateral constraints induced by a passive exoskeleton designed to replicate gastrocnemius contractures.

Methods

Kinematic data was collected as 10 healthy participants walked at a self-selected speed. A new Complexity-Instability Index (CII) of the leg motions was defined as a function of the Correlation Dimension and the Largest Lyapunov Exponent. Causal interactions between the leg motions are explored using Convergent Cross Mapping.

Results

Normal walking is characterized by a high mutual drive of each leg to the other, where CII is lowest for both legs (complexity of each leg motion is low and stability high). The effect of the bilateral emulated contractures is a reduced drive of each leg to the other and an increased CII for both legs. With unilateral emulated contracture, the mechanically constrained leg strongly drives the unconstrained leg, and CII was significantly higher for the constrained leg compared to normal walking.

Conclusion

Redundancy in limb motions is used to support causal interactions, reducing complexity and increasing stability in our leg dynamics during walking. The role of redundancy is to allow adaptability above being able to satisfy the overall biomechanical problem; and to allow the system to interact optimally. From an applied perspective, important characteristics of functional movement patterns might be captured by these nonlinear and causal variables, as well as the biomechanical aspects typically studied.

Using a contralateral shoe lift to reduce gait deterioration during an offloading fast-walk setting in diabetic peripheral neuropathy: A comparative feasibility study

AIMS

Diabetic peripheral neuropathy (DPN) is a predictor of foot ulcers and leads to sedentary behaviour. This comparative study evaluated gait and feasibility of a 20-minute fast walk, at 40-60% of cardiopulmonary capacity, in individuals with DPN wearing an offloading boot and a contralateral shoe balancer.

METHODS

Gait parameters were measured with inertial sensors on 32 individuals (group with DPN [n = 16], group with diabetes but without DPN [n = 9], and a group without diabetes/DPN [n = 7]). Feasibility was assessed by feedback on perceived effort and adverse events. Gait outcomes were compared between groups with or without a shoe balancer using one-way ANOVAs.

RESULTS

The three groups were equivalent in terms of activity level and age and gender except for the body mass index. Both groups with diabetes exhibited minimal decreased gait speed (p > 0.005) and the DPN group exhibited increased double-support percentage (+4.6%, p = 0.01) while walking with an offloading boot and contralateral shoe balancer. The use of a contralateral shoe balancer reduced gait asymmetry. Lower physical activity level was associated with further gait deterioration in all groups. Few adverse events were reported, and 91% of participants reported that the proposed activity would be feasible daily.

CONCLUSIONS

The offloading boot deteriorated gait function, but a contralateral shoe balancer minimized its impact, especially in the context of physical activity in people with diabetes and DPN.

The effect of loss of foot sole sensitivity on H-reflex of triceps surae muscles and functional gait

Objective: To investigate the effects of foot sole insensitivity on the outcomes of the triceps surae muscle H-reflex and functional gait. Material and Methods: People with peripheral neuropathy were recruited and divided into two groups: people with more (n = 13, 73.3 ± 4.3 years old) or less (n = 10, 73.5 ± 5.3) sensitive tactile sensation. Their monofilament testing scores were 9.0 ± 1.5 (range: 7-10) and 2.3 ± 2.4 (range: 0-6) out of 10, respectively. H-reflex of the triceps surae muscles during quiet standing and their relationship with functional gait, 6 min walking distance (6MWD), and timed-up-and-go duration (TUG), were compared between groups. Results: No significant difference was detected for H-reflex parameters between the groups. The less sensitive group showed reduced (p < .05) functional gait capacity compared to the other group, 38.4 ± 52.7 vs. 463.5 ± 47.6 m for 6MWD, and 9.0 ± 1.5 vs. 7.2 ± 1.1s for TUG, respectively. A significant correlation (p < .05), worse functional gait related to greater H/M ratio, was observed in the less sensitive group, not the other group. Conclusion: Although there was no significant H-reflex difference between the groups, more pronounced tactile sensation degeneration affected functional gaits and their relationship with H-reflex.

Nonlinear Analyses Distinguish Load Carriage Dynamics in Walking and Standing: A Systematic Review

Load carriage experiments are typically performed from a linear perspective that assumes that movement variability is equivalent to error or noise in the neuromuscular system. A complimentary, nonlinear perspective that treats variability as the object of study has generated important results in movement science outside load carriage settings. To date, no systematic review has yet been conducted to understand how load carriage dynamics change from a nonlinear perspective. The goal of this systematic review is to fill that need. Relevant literature was extracted and reviewed for general trends involving nonlinear perspectives on load carriage. Nonlinear analyses that were used in the reviewed studies included sample, multiscale, and approximate entropy; the Lyapunov exponent; fractal analysis; and relative phase. In general, nonlinear tools successfully distinguish between unloaded and loaded conditions in standing and walking, although not in a consistent manner. The Lyapunov exponent and entropy were the most used nonlinear methods. Two noteworthy findings are that entropy in quiet standing studies tends to decrease, whereas the Lyapunov exponent in walking studies tends to increase, both due to added load. Thus, nonlinear analyses reveal altered load carriage dynamics, demonstrating promise in applying a nonlinear perspective to load carriage while also underscoring the need for more research.

Sensory-Motor Mechanisms Increasing Falls Risk in Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is associated with peripheral sensory and motor nerve damage that affects up to half of diabetes patients and is an independent risk factor for falls. Clinical implications of DPN-related falls include injury, psychological distress and physical activity curtailment. This review describes how the sensory and motor deficits associated with DPN underpin biomechanical alterations to the pattern of walking (gait), which contribute to balance impairments underpinning falls. Changes to gait with diabetes occur even before the onset of measurable DPN, but changes become much more marked with DPN. Gait impairments with diabetes and DPN include alterations to walking speed, step length, step width and joint ranges of motion. These alterations also impact the rotational forces around joints known as joint moments, which are reduced as part of a natural strategy to lower the muscular demands of gait to compensate for lower strength capacities due to diabetes and DPN. Muscle weakness and atrophy are most striking in patients with DPN, but also present in non-neuropathic diabetes patients, affecting not only distal muscles of the foot and ankle, but also proximal thigh muscles. Insensate feet with DPN cause a delayed neuromuscular response immediately following foot–ground contact during gait and this is a major factor contributing to increased falls risk. Pronounced balance impairments measured in the gait laboratory are only seen in DPN patients and not non-neuropathic diabetes patients. Self-perception of unsteadiness matches gait laboratory measures and can distinguish between patients with and without DPN. Diabetic foot ulcers and their associated risk factors including insensate feet with DPN and offloading devices further increase falls risk. Falls prevention strategies based on sensory and motor mechanisms should target those most at risk of falls with DPN, with further research needed to optimise interventions.

Subjects With COPD Walk With Less Consistent Organization of Movement Patterns of the Lower Extremity

BACKGROUND

The inherent stride-to-stride fluctuations during walking are altered in the aging population and could provide insight into gait impairments and falls in patients with COPD. Stride-to-stride fluctuations are quantified two ways: variability of the fluctuations (eg, standard deviation), and movement patterns within the fluctuations. Our objective was to investigate stride-to-stride fluctuations by evaluating the variability and movement patterns of lower limb joints in subjects with COPD compared to subjects without COPD as control subjects.

METHODS

In this cross-sectional study, 22 subjects with COPD (age 63 ± 9 y; FEV₁ 54 ± 19% predicted) and 22 control subjects (age 62 ± 9 y; FEV₁ 95 ± 18% predicted) walked for 3 min on a treadmill while their gait was recorded. The amount of variability (ie, standard deviation and coefficient of variation) and movement patterns (ie, predictability and consistency in organization) were quantified for the range of motion and joint angle of the hip, knee, and ankle, at 3 walking speeds (ie, self-selected, fast, and slow). General linear mixed models were used for analysis.

RESULTS

Control subjects had more consistent organization of the hip and knee joint movement patterns compared to subjects with COPD (P = .02 and P = .02, respectively). Further, control subjects adapted to speed changes by demonstrating more consistent organization of movement patterns with faster speeds, whereas subjects with COPD did not. At the fast walking speed, subjects with COPD demonstrated less consistent organization of knee and hip joint movement patterns as compared to control subjects without COPD (P = .03 and P = .005, respectively). The amount of variability did not differ between groups.

CONCLUSIONS

Although subjects with COPD did not demonstrate decreased amount of variability, their hip and knee joint movement patterns were less consistent in organization during walking. Reduced consistency in organization of movement patterns may be a contributing factor to falls and mobility problems experienced by patients with COPD.

Objective parameters to measure (in)stability of the knee joint during gait: A review of literature

BACKGROUND

Instability of the knee joint during gait is frequently reported by patients with knee osteoarthritis or an anterior cruciate ligament rupture. The assessment of instability in clinical practice and clinical research studies mainly relies on self-reporting. Alternatively, parameters measured with gait analysis have been explored as suitable objective indicators of dynamic knee (in)stability.

RESEARCH QUESTION

This literature review aimed to establish an inventory of objective parameters of knee stability during gait.

METHODS

Five electronic databases (Pubmed, Embase, Cochrane, Cinahl and SPORTDiscuss) were systematically searched, with keywords concerning knee, stability and gait. Eligible studies used an objective parameter(s) to assess knee (in)stability during gait, being stated in the introduction or methods section. Out of 10717 studies, 89 studies were considered eligible.

RESULTS

Fourteen different patient populations were investigated with kinematic, kinetic and/or electromyography measurements during (challenged) gait. Thirty-three possible objective parameters were identified for knee stability, of which the majority was based on kinematic (14 parameters) or electromyography (12 parameters) measurements. Thirty-nine studies used challenged gait (i.e. external perturbations, downhill walking) to provoke knee joint instability. Limited or conflicting results were reported on the validity of the 33 parameters.

SIGNIFICANCE

In conclusion, a large number of different candidates for an objective knee stability gait parameter were found in literature, all without compelling evidence. A clear conceptual definition for dynamic knee joint stability is lacking, for which we suggest : "The capacity to respond to a challenge during gait within the natural boundaries of the knee". Furthermore biomechanical gait laboratory protocols should be harmonized, to enable future developments on clinically relevant measure(s) of knee stability during gait.

The Effect of Diabetic Peripheral Neuropathy on Ground Reaction Forces during Straight Walking in Stroke Survivors

Purpose. The aim of this present study was to investigate the ground reaction forces (GRFs) alterations in stroke survivors with diabetic peripheral neuropathy (DPN). Methods. Ten stroke survivors with DPN, 10 stroke survivors without DPN, and 10 healthy controls with matched body weight between groups participated in this case-control cross-sectional study. Three-dimensional GRFs (anterior-posterior, medial-lateral, and vertical) were collected at a comfortable walking speed using the Nexus Vicon motion analysis system and force plate. The Kruskal–Wallis test was used to analyze GRFs parameters. Results. We found significant alterations of medial-lateral forces of the nonparetic side and vertical forces of the paretic side in stroke survivors with DPN compared to stroke survivors without DPN and healthy controls. In addition, there were smaller braking and lower propulsion peak in anterior-posterior forces, smaller magnitude of medial-lateral forces, and lower first and second peak of vertical forces in stroke survivors with DPN compared to stroke survivors without DPN and healthy controls. Conclusion. The study findings identified that GRFs were affected in stroke survivors with DPN on both the paretic and the nonparetic sides. Further investigations are warranted to explore the impact of DPN on the kinematics and muscle activity related to the gait performance in stroke survivors with DPN.

Postural Control and Gait Performance in the Diabetic Peripheral Neuropathy: A Systematic Review

Purpose. The aim of this paper is to review the published studies on the characteristics of impairments in the postural control and gait performance in diabetic peripheral neuropathy (DPN). Methods. A review was performed by obtaining publication of all papers reporting on the postural control and gait performance in DPN from Google Scholar, Ovid, SAGE, Springerlink, Science Direct (SD), EBSCO Discovery Service, and Web of Science databases. The keywords used for searching were “postural control,” “balance,” “gait performance,” “diabetes mellitus,” and “diabetic peripheral neuropathy.” Results. Total of 4,337 studies were hit in the search. 1,524 studies were screened on their titles and citations. Then, 79 studies were screened on their abstract. Only 38 studies were eligible to be selected: 17 studies on postural control and 21 studies on the gait performance. Most previous researches were found to have strong evidence of postural control impairments and noticeable gait deficits in DPN. Deterioration of somatosensory, visual, and vestibular systems with the pathologic condition of diabetes on cognitive impairment causes further instability of postural and gait performance in DPN. Conclusions. Postural instability and gait imbalance in DPN may contribute to high risk of fall incidence, especially in the geriatric population. Thus, further works are crucial to highlight this fact in the hospital based and community adults.

Pain, sleep disturbances, and functional limitations in people living with HIV/AIDS-associated distal sensory peripheral neuropathy

BACKGROUND

Pain, sleep, and functional disturbances are a common occurrence in people living with HIV/AIDS-related distal sensory peripheral neuropathy (PLWHA-DSPN) yet lack group classification and quantification.

METHODS

A total of 46 PLWHA-DSPN were recruited, as part of a 2-group intervention study, to complete the Neuropathic Pain Scale and the Pittsburgh Sleep Quality Index (PSQI) questionnaires. The participant's performance during a forward reach task and walking distance in 6 minutes was recorded as a measure of function.

RESULTS

The pain (60.77 +/- 17.85) and sleep (14.62 +/- 4.28) scores denote marked pain and sleep disturbances, compared to seronegative, age-matched individuals. The ambulation distance was limited (243.99 +/- 141.04 m) and inversely associated with the PSQI-sleep efficiency subscale (rs = -.35, P < .05). The average reaching distances measured (36.07 +/- 7.37 cm) were similar to seronegative, age-matched individuals. Pain, sleep, and functional measures exhibited significant associations.

CONCLUSIONS

The data collected suggest that PLWHA-DSPN report moderate-to-severe pain and significant sleep disturbances and exhibit limited ambulation distances.

A shoe insole delivering subsensory vibratory noise improves balance and gait in healthy elderly people

OBJECTIVES

To test whether subsensory vibratory noise applied to the sole of the foot using a novel piezoelectric vibratory insole can significantly improve sensation, enhance balance, and reduce gait variability in elderly people, as well as to determine the optimal level of vibratory noise and whether the therapeutic effect would endure and the user's sensory threshold would remain constant during the course of a day.

DESIGN

A randomized, single-blind, crossover study of 3 subsensory noise stimulation levels on 3 days.

SETTING

Balance and gait laboratory.

PARTICIPANTS

Healthy community-dwelling elderly volunteers (N=12; age, 65-90y) who could feel the maximum insole vibration.

INTERVENTIONS

A urethane foam insole with the piezoelectric actuators delivering subsensory vibratory noise stimulation to the soles of the feet.

MAIN OUTCOME MEASURES

Balance, gait, and timed Up and Go (TUG) test.

RESULTS

The vibratory insoles significantly improved performance on the TUG test, reduced the area of postural sway, and reduced the temporal variability of walking at both 70% and 85% of the sensory threshold and during the course of a day. Vibratory sensation thresholds remained relatively stable within and across study days.

CONCLUSIONS

This study provides proof of concept that the application of the principle of stochastic resonance to the foot sole sensory system using a new low-voltage piezoelectric technology can improve measures of balance and gait that are associated with falls. Effective vibratory noise amplitudes range from 70% to 85% of the sensory threshold and can be set once daily.

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.

Using dynamic walking models to identify factors that contribute to increased risk of falling in older adults

Falls are common in older adults. The most common cause of falls is tripping while walking. Simulation studies demonstrated that older adults may be restricted by lower limb strength and movement speed to regain balance after a trip. This review examines how modeling approaches can be used to determine how different measures predict actual fall risk and what some of the causal mechanisms of fall risk are. Although increased gait variability predicts increased fall risk experimentally, it is not clear which variability measures could best be used, or what magnitude of change corresponded with increased fall risk. With a simulation study we showed that the increase in fall risk with a certain increase in gait variability was greatly influenced by the initial level of variability. Gait variability can therefore not easily be used to predict fall risk. We therefore explored other measures that may be related to fall risk and investigated the relationship between stability measures such as Floquet multipliers and local divergence exponents and actual fall risk in a dynamic walking model. We demonstrated that short-term local divergence exponents were a good early predictor for fall risk. Neuronal noise increases with age. It has however not been fully understood if increased neuronal noise would cause an increased fall risk. With our dynamic walking model we showed that increased neuronal noise caused increased fall risk. Although people who are at increased risk of falling reduce their walking speed it had been questioned whether this slower speed would actually cause a reduced fall risk. With our model we demonstrated that a reduced walking speed caused a reduction in fall risk. This may be due to the decreased kinematic variability as a result of the reduced signal-dependent noise of the smaller muscle forces that are required for slower. These insights may be used in the development of fall prevention programs in order to better identify those at increased risk of falling and to target those factors that influence fall risk most.

Assessment of gait sensitivity norm as a predictor of risk of falling during walking in a neuromusculoskeletal model

Quantifying the risk of falling (falls risk) would be helpful in treating people with gait disorders. The gait sensitivity norm (GSN) is a stability measure that correlates well to risk of falling in passive dynamic walkers but has not been evaluated on humans or human-like walking models. We assessed the correlation of GSN to risk of falling in a neuromusculoskeletal (NMS) walking model. Specifically, we evaluated the correlation of GSN to the actual disturbance rejection (ADR) of the model and the sensitivity of this relationship to gait parameter, Poincaré section selection and steady state variability correction. Statistically significant results at p<0.05 were obtained for some of the gait indicators evaluated at the point in the gait cycle where they were most variable. The correlation between GSN and ADR was sensitive to gait indicator and Poincaré sections evaluated but not to steady state variability correction. The current work suggests some simple steps to reduce the sensitivity of GSN to arbitrary and subjective factors. Overall, the findings support the potential of GSN to be a clinically applicable measure of falls risk. Further study is required to identify methods to more definitively select the various factors within the GSN calculation and to confirm its ability to predict falls risk in human subjects.

Influence of neuromuscular noise and walking speed on fall risk and dynamic stability in a 3D dynamic walking model

Older adults and those with increased fall risk tend to walk slower. They may do this voluntarily to reduce their fall risk. However, both slower and faster walking speeds can predict increased risk of different types of falls. The mechanisms that contribute to fall risk across speeds are not well known. Faster walking requires greater forward propulsion, generated by larger muscle forces. However, greater muscle activation induces increased signal-dependent neuromuscular noise. These speed-related increases in neuromuscular noise may contribute to the increased fall risk observed at faster walking speeds. Using a 3D dynamic walking model, we systematically varied walking speed without and with physiologically-appropriate neuromuscular noise. We quantified how actual fall risk changed with gait speed, how neuromuscular noise affected speed-related changes in fall risk, and how well orbital and local dynamic stability measures predicted changes in fall risk across speeds. When we included physiologically-appropriate noise to the 'push-off' force in our model, fall risk increased with increasing walking speed. Changes in kinematic variability, orbital, and local dynamic stability did not predict these speed-related changes in fall risk. Thus, the increased neuromuscular variability that results from increased signal-dependent noise that is necessitated by the greater muscular force requirements of faster walking may contribute to the increased fall risk observed at faster walking speeds. The lower fall risk observed at slower speeds supports experimental evidence that slowing down can be an effective strategy to reduce fall risk. This may help explain the slower walking speeds observed in older adults and others.

The relationship between brain volume and walking outcomes in older adults with and without diabetic peripheral neuropathy

OBJECTIVE

Diabetic peripheral neuropathy (DPN) alters walking. Yet, the compensatory role of central locomotor circuits remains unclear. We hypothesized that walking outcomes would be more closely related to regional gray matter volumes in older adults with DPN as compared with nonneuropathic diabetic patients and nondiabetic control subjects.

RESEARCH DESIGN AND METHODS

Clinically important outcomes of walking (i.e., speed, stride duration variability, and double support time) were measured in 29 patients with DPN (type 2 diabetes with foot-sole somatosensory impairment), 68 diabetic (DM) patients (type 2 diabetes with intact foot-sole sensation), and 89 control subjects. Global and regional gray matter volumes were calculated from 3 Tesla magnetic resonance imaging.

RESULTS

DPN subjects walked more slowly (P = 0.005) with greater stride duration variability (P < 0.001) and longer double support (P < 0.001) as compared with DM and control subjects. Diabetes was associated with less cerebellar gray matter volume (P < 0.001), but global gray matter volume was similar between groups. DPN subjects with lower gray matter volume globally (P < 0.004) and regionally (i.e., cerebellum, right-hemisphere dorsolateral prefrontal cortex, basal ganglia, P < 0.005) walked more slowly with greater stride duration variability and/or longer double support. Each relationship was stronger in DPN than DM subjects. In control subjects, brain volumes did not relate to walking patterns.

CONCLUSIONS

Strong relationships between brain volumes and walking outcomes were observed in the DPN group and to a lesser extent the DM group, but not in control subjects. Individuals with DPN may be more dependent upon supraspinal elements of the motor control system to regulate several walking outcomes linked to poor health in elderly adults.

Electromyography and kinematic changes of gait cycle at different cadences in diabetic neuropathic individuals

INTRODUCTION

Changes in gait cadence caused by challenging situations in daily life might induce higher demand for strength and propulsion in diabetic neuropathic (DN) subjects.

METHODS

Forty-six subjects (healthy and DN) walked at two cadences (self-selected and 25% higher). Kinematic and electromyographic data were obtained from lower limbs and compared across the gait cycle.

RESULTS

DN subjects showed a delayed peak in plantarflexor activity along the whole cycle (irrespective of cadence) compared with healthy subjects. However, during the imposed cadence, DN individuals showed reduced ankle range of motion along the entire cycle compared with the self-selected condition and healthy individuals walking at both cadences (P = 0.002).

CONCLUSIONS

These findings suggest that when diabetic individuals face a new challenging situation that induces a higher demand for muscle strength and propulsion, the necessary range of motion and neuromuscular control around distal joints are insufficient.

Long term Tai Chi exercise improves physical performance among people with peripheral neuropathy

This study examined the effects of a 24-week Tai Chi intervention on physical function in individuals with peripheral neuropathy. Twenty-five women and men with peripheral neuropathy were recruited. Plantar pressure detection threshold was assessed with a 5.07 gauge monofilament. Functional gait was assessed by the 6-min walk and timed up-and-go tests. Isokinetic leg strength and standing balance was also assessed. Twenty-four consecutive weeks of modified, group-based Tai Chi practice was completed, with testing repeated every six weeks throughout. No adverse events were observed and attendance was 17 +/- 4 sessions per 6 weeks. After 6 weeks of Tai Chi, participants increased 6-min walk (P < 0.0001), timed up-and-go (P < 0.0001), and leg strength (P < 0.01) performance. Continued improvement was observed in the timed up-and-go. Plantar sensation improved (P = 0.003) following the Tai Chi intervention. Group-based Tai Chi is a safe, plausible, and effective intervention for those with PN.

Peripheral nerve conduction abnormalities in nonparetic side of ischemic stroke patients

Cardiovascular diseases manifest similar age and sex distribution in the general population and have some commons risk factors with some neuropathies. The aim of this study is to verify whether standard nerve conduction studies show significant differences in a group of poststroke hemiplegic patients, when compared with a control group, in the hypothesis that stroke, as a primary cardiovascular event, could be strongly associated with peripheral nervous system disease. Nerve conduction studies were performed in 15 hemiplegic patients and 10 aged matched control subjects. Percentage of patients showing slowed ulnar and common peroneal motor nerve conduction and lower ulnar sensory nerve action potential was significantly higher in hemiplegic patients. These findings suggest that an overall increased risk of neuropathies could be detected among stroke patients.

Characteristics of functional gait among people with and without peripheral neuropathy

It is advantageous from a rehabilitation standpoint to determine physiological factors associated with functional gait. These factors may be fundamentally different in those with peripheral neuropathy (PN) compared to age-matched healthy individuals. The purpose of this investigation was to examine associations between functional gait and measures of leg strength, standing balance, and locomotor kinematics in people with and without PN.

METHODS

Individuals with PN and age-matched controls were assessed for functional gait by the 6-min walk and timed up-and-go tests. Leg strength was measured as isokinetic peak torque of the knee extensors. Standing balance was assessed by center-of-pressure sway velocity and area during quiet stance. Locomotor kinematics from treadmill walking were used to compute stride duration variability and local instability (i.e., finite-time Lyapunov exponents), which estimate kinematic divergence caused by small-scale perturbations.

RESULTS

Leg strength and locomotor kinematics - in particular local instability - correlated with functional gait performance in controls. Conversely, reduced functional gait performance in the PN group was primarily mediated by impaired standing balance control.

DISCUSSION

Locomotor kinematics predicts functional gait, and the magnitude of variability and local instability should be calculated to fully evaluate locomotor system health. The observation that different factors associated with functional gait between groups speaks to the uniqueness of the PN-related movement disorder. Functional gait-related rehabilitation programs for PN patients should be tailored toward this uniqueness.

Nonlinear time series analysis of knee and ankle kinematics during side by side treadmill walking

Nonlinear time series analysis was used to estimate maximal Lyapunov exponents of select ankle and knee kinematics during three different conditions of treadmill walking: independent, side by side, and side by side with forced synchronization of stepping. Stride to stride variability was significantly increased for the condition in which individuals walked side by side and synchronized unintentionally when compared to the conditions of forced synchronization and independent walking. In addition, standard deviations of three kinematic variables of lower extremity movement were significantly increased during the condition in which unintentional synchronization occurred. No relationship was found between standard deviation and estimates of maximal Lyapunov exponents. An increase in kinematic variability during side by side walking for nonimpaired individuals who are not at risk of falling suggests that variability in certain aspects of performance might be indicative of a healthy system. Modeling this variability for an impaired individual to imitate may have beneficial effects on locomotor function. These results may therefore have implications for the rehabilitation of gait in humans by suggesting that a different functional outcome might be achieved by practicing side by side walking as opposed to more commonly used strategies involving independent walking.

Comparison of different state space definitions for local dynamic stability analyses

Measures of local dynamic stability, such as the local divergence exponent (lambda*(s)) quantify how quickly small perturbations deviate from an attractor that defines the motion. When the governing equations of motion are unknown, an attractor can be reconstructed by defining an appropriate state space. However, state space definitions are not unique and accepted methods for defining state spaces have not been established for biomechanical studies. This study first determined how different state space definitions affected lambda*(s) for the Lorenz attractor, since exact theoretical values were known a priori. Values of lambda*(s) exhibited errors <10% for 7 of the 9 state spaces tested. State spaces containing redundant information performed the poorest. To examine these effects in a biomechanical context, 20 healthy subjects performed a repetitive sawing-like task for 5 min before and after fatigue. Local stability of pre- and post-fatigue shoulder movements was compared for 6 different state space definitions. Here, lambda*(s)decreased post-fatigue for all 6 state spaces. Differences were statistically significant for 3 of these state spaces. For state spaces defined using delay embedding, increasing the embedding dimension decreased lambda*(s) in both the Lorenz and experimental data. Overall, our findings suggest that direct numerical comparisons between studies that use different state space definitions should be made with caution. However, trends across experimental comparisons appear to persist. Biomechanical state spaces constructed using positions and velocities, or delay reconstruction of individual states, are likely to provide consistent results.