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BackgroundDirect electrical activation of skeletal muscles of patients with upper motor neuron lesions can restore functional movements, such as standing or walking. Because responses to electrical stimulation are highly nonlinear and time varying, accurate control of muscles to produce functional movements is very difficult. Accurate and predictive mathematical models can facilitate the design of stimulation patterns and control strategies that will produce the desired force and motion. In the present study, we build upon our previous isometric model to capture the effects of constant angular velocity on the forces produced during electrically elicited concentric contractions of healthy human quadriceps femoris muscle. Modelling the isovelocity condition is important because it will enable us to understand how our model behaves under the relatively simple condition of constant velocity and will enable us to better understand the interactions of muscle length, limb velocity, and stimulation pattern on the force produced by the muscle.MethodsAn additional term was introduced into our previous isometric model to predict the force responses during constant velocity limb motion. Ten healthy subjects were recruited for the study. Using a KinCom dynamometer, isometric and isovelocity force data were collected from the human quadriceps femoris muscle in response to a wide range of stimulation frequencies and patterns. % error, linear regression trend lines, and paired t-tests were used to test how well the model predicted the experimental forces. In addition, sensitivity analysis was performed using Fourier Amplitude Sensitivity Test to obtain a measure of the sensitivity of our model's output to changes in model parameters.ResultsPercentage RMS errors between modelled and experimental forces determined for each subject at each stimulation pattern and velocity showed that the errors were in general less than 20%. The coefficients of determination between the measured and predicted forces show that the model accounted for approximately 86% and approximately 85% of the variances in the measured force-time integrals and peak forces, respectively.ConclusionThe range of predictive abilities of the isovelocity model in response to changes in muscle length, velocity, and stimulation frequency for each individual make it ideal for dynamic applications like FES cycling.

BackgroundFunctional electrical stimulation (FES) has been used to improve function in individuals with hemiparesis following stroke. An ideal functional electrical stimulation (FES) system needs an accurate mathematical model capable of designing subject and task-specific stimulation patterns. Such a model was previously developed in our laboratory and shown to predict the isometric forces produced by the quadriceps femoris muscles of able-bodied individuals and individuals with spinal cord injury in response to a wide range of clinically relevant stimulation frequencies and patterns. The aim of this study was to test our isometric muscle force model on the quadriceps femoris, ankle dorsiflexor, and ankle plantar-flexor muscles of individuals with post-stroke hemiparesis.MethodsSubjects were seated on a force dynamometer and isometric forces were measured in response to a range of stimulation frequencies (10 to 80-Hz) and 3 different patterns. Subject-specific model parameter values were obtained by fitting the measured force responses from 2 stimulation trains. The model parameters thus obtained were then used to obtain predicted forces for a range of frequencies and patterns. Predicted and measured forces were compared using intra-class correlation coefficients, r2 values, and model error relative to the physiological error (variability of measured forces).ResultsResults showed excellent agreement between measured and predicted force-time responses (r2 >0.80), peak forces (ICCs>0.84), and force-time integrals (ICCs>0.82) for the quadriceps, dorsiflexor, and plantar-fexor muscles. The model error was within or below the +95% confidence interval of the physiological error for >88% comparisons between measured and predicted forces.ConclusionOur results show that the model has potential to be incorporated as a feed-forward controller for predicting subject-specific stimulation patterns during FES.

Background: Walking dysfunctions persist following poststroke rehabilitation. A major limitation of current rehabilitation efforts is the inability to identify modifiable deficits that, when improved, will result in the recovery of walking function. Previous studies have relied on cross-sectional analyses to identify deficits to target during walking rehabilitation; however, these studies did not account for the influence of a key covariate - maximum walking speed. Objective: To determine the relationships between commonly studied poststroke variables and the long-distance walking function of individuals poststroke when controlling for maximum walking speed. Methods: Correlation analyses of cross-sectional data from 57 individuals more than 6 months poststroke measured the relationships between standing balance, walking balance, balance self-efficacy, lower extremity motor function, and maximum walking speed versus long-distance walking function. For a subgroup of subjects who completed training, the relationship between changes in maximum walking speed versus changes in long-distance walking function was assessed. Results: Each measurement of interest strongly correlated with long-distance walking function (rs from 0.448 to 0.900, all Ps ≤ .001); however, when controlling for maximum walking speed, none of the other measurements remained related to long-distance walking function. In contrast, when controlling for each of the other measurements, maximum walking speed remained highly related. Moreover, changes in maximum walking speed resulting from training were highly related to changes in long-distance walking function (r = .737, P ≤ .001). Conclusions: For individuals in the chronic phase of stroke recovery, improving maximum walking speed may be necessary to improve long-distance walking function. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: To determine the feasibility and safety of implementing a 12-week locomotor intervention targeting paretic propulsion deficits during walking through the joining of 2 independent interventions, walking at maximal speed on a treadmill and functional electrical stimulation of the paretic ankle musculature (FastFES); to determine the effects of FastFES training on individual subjects; and to determine the influence of baseline impairment severity on treatment outcomes. Design: Single group pre-post preliminary study investigating a novel locomotor intervention. Setting: Research laboratory. Participants: Individuals (N=13) with locomotor deficits after stroke. Intervention: FastFES training was provided for 12 weeks at a frequency of 3 sessions per week and 30 minutes per session. Main Outcome Measures: Measures of gait mechanics, functional balance, short- and long-distance walking function, and self-perceived participation were collected at baseline, posttraining, and 3-month follow-up evaluations. Changes after treatment were assessed using pairwise comparisons and compared with known minimal clinically important differences or minimal detectable changes. Correlation analyses were run to determine the correlation between baseline clinical and biomechanical performance versus improvements in walking speed. Results: Twelve of the 13 subjects that were recruited completed the training. Improvements in paretic propulsion were accompanied by improvements in functional balance, walking function, and self-perceived participation (each P<.02)—all of which were maintained at 3-month follow-up. Eleven of the 12 subjects achieved meaningful functional improvements. Baseline impairment was predictive of absolute, but not relative, functional change after training. Conclusions: This report demonstrates the safety and feasibility of the FastFES intervention and supports further study of this promising locomotor intervention for persons poststroke. [Copyright &y& Elsevier]

Background: Walking speed has been used to predict the efficacy of gait training; however, poststroke motor impairments are heterogeneous and different biomechanical strategies may underlie the same walking speed. Identifying which individuals will respond best to a particular gait rehabilitation program using walking speed alone may thus be limited. The objective of this study was to determine if, beyond walking speed, participants’ baseline ability to generate propulsive force from their paretic limbs (paretic propulsion) influences the improvements in walking speed resulting from a paretic propulsion-targeting gait intervention. Methods: Twenty seven participants >6 months poststroke underwent a 12-week locomotor training program designed to target deficits in paretic propulsion through the combination of fast walking with functional electrical stimulation to the paretic ankle musculature (FastFES). The relationship between participants’ baseline usual walking speed (UWSbaseline), maximum walking speed (MWSbaseline), and paretic propulsion (propbaseline) versus improvements in usual walking speed (∆UWS) and maximum walking speed (∆MWS) were evaluated in moderated regression models. Results: UWSbaseline and MWSbaseline were, respectively, poor predictors of ΔUWS (R2 = 0.24) and ΔMWS (R2 = 0.01). Paretic propulsion × walking speed interactions (UWSbaseline × propbaseline and MWSbaseline × propbaseline) were observed in each regression model (R2s = 0.61 and 0.49 for ∆UWS and ∆MWS, respectively), revealing that slower individuals with higher utilization of the paretic limb for forward propulsion responded best to FastFES training and were the most likely to achieve clinically important differences. Conclusions: Characterizing participants based on both their walking speed and ability to generate paretic propulsion is a markedly better approach to predicting walking recovery following targeted gait rehabilitation than using walking speed alone.

Background: A common goal of persons post-stroke is to regain community ambulation. The plantar flexor muscles play an important role in propulsion generation and swing initiation as previous musculoskeletal simulations have shown. The purpose of this study was to demonstrate that simulation results quantifying changes in plantar flexor activation and function in individuals post-stroke were consistent with (1) the purpose of an intervention designed to enhance plantar flexor function and (2) expected muscle function during gait based on previous literature. Methods: Three-dimensional, forward dynamic simulations were created to determine the changes in model activation and function of the paretic ankle plantar flexor muscles for eight patients post-stroke after a 12-weeks FastFES gait retraining program. Results: An median increase of 0.07 (Range [-0.01,0.22]) was seen in simulated activation averaged across all plantar flexors during the double support phase of gait from pre- to post-intervention. A concurrent increase in walking speed and plantar flexor induced forward center of mass acceleration by the plantar flexors was seen post-intervention for seven of the eight subject simulations. Additionally, post-training, the plantar flexors had an simulated increase in contribution to knee flexion acceleration during double support. Conclusions: For the first time, muscle-actuated musculoskeletal models were used to simulate the effect of a gait retraining intervention on post-stroke muscle model predicted activation and function. The simulations showed a new pattern of simulated activation for the plantar flexor muscles after training, suggesting that the subjects activated these muscles with more appropriate timing following the intervention. Functionally, simulations calculated that the plantar flexors provided greater contribution to knee flexion acceleration after training, which is important for increasing swing phase knee flexion and foot clearance [ABSTRACT FROM AUTHOR]

Background: The energy cost of transport is higher for persons with stroke compared with neurologically intact subjects, and this has a negative impact on ambulatory activity and function. Whether the high energy cost of walking after stroke is influenced by gait training interventions is generally not considered. Objective: To examine changes in the energy cost of transport with a gait training intervention after stroke and to identify whether energy cost changes independent of changes in walking speed. Methods: Persons with chronic (&nvgt;6 months) stroke participated in an intervention combining fast walking and functional electrical stimulation of the ankle dorsi-and plantarflexor muscles. Oxygen consumption, walking speed, and endurance were measured pre and post training. Energy and caloric cost of transport were calculated at self-selected and absolute speeds at each time point. Results: Eleven subjects (age 61.8 ± 8 years) participated. Self-selected and fastest walking speed and 6-minute walk test distance improved after the intervention (F = 67.5, P < .001; F = 40.9, P < .001; F = 20.2, P = .001, respectively). Energy and caloric cost of transport at self-selected speed improved (F = 8.63, P = .015, and F = 7.87, P = .019, respectively) but did not change at an absolute speed pre-to postintervention. Conclusions: Energy and caloric cost of transport at self-selected walking speeds improved pre to post training but were unaffected at an absolute walking speed, suggesting that the improved energy cost of transport was through improvements in the subject's self-selected walking speed. These results illustrate that improvements in walking speed following an intervention are an important mechanism by which the energy cost of transport can be reduced post stroke. [ABSTRACT FROM AUTHOR]

Stroke leads to gait impairments that can negatively influence quality of life. Functional electrical stimulation (FES) applied during fast walking (FastFES) is an effective gait rehabilitation strategy that can lead to improvements in gait performance, walking speed and endurance, balance, activity, and participation poststroke. The effect of FastFES gait training on mechanical energy utilization is not well understood. The objective of this study was to test the effects of 12 weeks of FastFES gait training on mechanical recovery indices of poststroke gait. Kinematic data were collected from 11 stroke survivors before and after 12 weeks of FastFES training. Mechanical recovery was calculated from the positive changes in vertical, anterior-posterior, and medial-lateral components of center of mass energy. The average mechanical recovery increased from 34.5% before training to 40.0% after training. The increase was statistically significant ( P = 0.014). The average self-selected walking speed increased from 0.4 m/s to 0.7 m/s after the 12-week FastFES training. The results indicate that the subjects were better able to generate and utilize the external mechanical energy of walking after FastFES gait training. FastFES gait training has the capacity to increase the gait speed, improve the mechanical recovery, and reduce the mechanical energy expenditure of stroke survivors when they walk. [ABSTRACT FROM AUTHOR]

Abstract: Post-stroke gait impairments are common and result in slowed walking speeds and decreased community participation post-stroke. Treadmill training has recently emerged as an effective gait rehabilitation intervention. Furthermore, kinematic and kinetic data collected during treadmill walking are commonly used for assessing gait performance. The minimal detectable change (MDC) for gait variables provides a useful index to determine whether the magnitude of change in gait produced after an intervention is greater than the amount of change attributable to day-to-day variability in gait or test–retest measurement errors. The MDC values for kinematic, ground reaction force (GRF), spatial, and temporal variables collected during treadmill walking post-stroke have not been previously reported. The objective of this study was, therefore, to compute MDCs for post-stroke gait kinematics, GRF indices, temporal, and spatial measures during treadmill walking. Nineteen individuals with chronic post-stroke hemiparesis (12 males; age=47–75 years; 72.6±63.4 months since stroke) participated in 2 testing sessions separated by 20.7±26.8 days. Our results showed that test–retest reliability was excellent for all gait variables tested (intraclass correlation coefficients=0.799–0.986). MDCs were reported for hip, knee, and ankle joint angles (range 3.8° for trailing limb angles to 11.5° for hip extension), peak anterior GRF (2.85% body weight), mean vertical GRF (4.65% body weight), all temporal variables (range 3.2–4.2% gait cycle), and paretic step length (6.7cm). These MDCs provide a useful reference to help interpret the magnitudes of changes in post-stroke gait variables. [Copyright &y& Elsevier]

Rationale: This case report describes the application of a novel gait retraining approach to an individual with poststroke hemiparesis. The rehabilitation protocol combined a specially designed leg or- thosis (the gravity-balanced orthosis), treadmill walking, and functional electrical stimulation to the ankle muscles with the application of motor learning principles. Case: The participant was a 58-year-old man who had a stroke more than three years before the intervention. He underwent gait retraining over a period of five weeks for a total of 15 sessions during which the gravity compensation provided by the gravity-balanced orthosis and visual feedback about walking performance was gradually reduced. Outcomes: At the end of five weeks, he decreased the time required to complete the Timed Up and Go test; his gait speed increased during overground walking; gait was more symmetrical; stride length, hip and knee joint excursions on the affected side increased. Except for gait symmetry, all other improvements were maintained one month post-intervention. Conclusions: This case report describes possible advantages of judiciously combining different treatment techniques in improving the gait of chronic stroke survivors. Further studies are planned to evaluate the effectiveness of different components of this training in both the subacute and chronic stages of stroke recovery. [ABSTRACT FROM AUTHOR]

Abstract: Chou L-W, Lee SC, Johnston TE, Binder-Macleod SA. The effectiveness of progressively increasing stimulation frequency and intensity to maintain paralyzed muscle force during repetitive activation in persons with spinal cord injury. Objective: To compare the effectiveness of progressively increasing stimulation intensity, progressively increasing frequency, or progressively increasing both frequency and intensity on paralyzed quadriceps femoris muscle force maintenance during repetitive activation. Design: Factorial design with different stimulation protocols as independent variables. Setting: A muscle performance laboratory. Participants: People (N=8) with spinal cord injury (SCI) (age, 14.63±1.77y). Interventions: Not applicable. Main Outcome Measure: Number of contractions when the peak force was 90% or more of a subject''s maximal twitch force. Results: The protocol involving progressively increasing stimulation intensity and then frequency generated more successful contractions (189.88±53.33) than progressively increasing the frequency followed by intensity (122.75±26.56 contractions). Regardless of the order, progressively increasing both intensity and frequency generated more successful contractions than progressively increasing intensity (97 contractions) or frequency (62 contractions) alone. Conclusions: Our findings suggest that during repetitive electric activation, progressively increasing both stimulation frequency and intensity can produce more successful contractions than progressively increasing only frequency or intensity. These findings can help researchers and clinicians design more effective stimulation protocols for persons with SCI during functional electric stimulation applications. [Copyright &y& Elsevier]

The article focuses on a study which examined the association of angiotensin-converting enzyme (ACE) and other genetic factors with selected measures of physical performance. ACE is part of the renin-angiotensin system. The gene catalyzes the conversion of the angiotensin I to produce angiotensin II. It also degrades the potent vasolidator bradykinin. The polymorphism of the ACE gene is classified by the presence or absence of a DNA sequence within the ACE gene. Possible associations of the ACE polymorphism have ben investigated to determine whether the I and D alleles of the ACE gene gives an advantage for athletic performance. Two theories have been posed regarding the possible physiological mechanisms involving the ACE I/D polymorphism The first theory is that the ACE polymorphism may later physical performance through a metabolic response associated with the I allele.

Abstract: Kebaetse MB, Lee SC, Johnston TE, Binder-Macleod SA. Strategies that improve paralyzed human quadriceps femoris muscle performance during repetitive, nonisometric contractions. Objective: To determine the effect of combining different stimulation frequencies on the ability of paralyzed human quadriceps muscle to produce a 50° knee excursion repetitively when starting at 90° of flexion. Design: Repeated-measures design. Setting: Clinical research laboratory. Participants: Complete data were collected from 9 subjects aged 11 to 25 years (mean ± standard deviation, 17.1±4.5y) with spinal cord injury (SCI). Intervention: Three protocols were each tested during separate sessions: 20-Hz trains of pulses followed by 66-Hz trains (C20+66), 33-Hz trains followed by 66-Hz trains (C33+66), and 66-Hz trains alone (C66). For each frequency, stimulation was repeated until the knee failed to produce a 50° excursion. This approach allowed us to evaluate the response to stimulation with 20-, 33-, and 66-Hz and combinations of 20- and 66-Hz and 33- and 66-Hz trains. Main Outcome Measure: Number of successful contractions. Results: The C20 and C33 did not differ (mean, 41.0±12.6 excursions and 42.0±12.3 excursions, respectively), and each produced more excursions than the C66 protocol. The C20+66 and C33+66 protocols produced 51.4±15.0 and 44.9±13.6 excursions, respectively, and the C20+66 was the best protocol overall (all P≤.05). Conclusions: This study showed that stimulation strategies that start with low frequencies and switch to higher frequencies as the muscle fatigues could improve the ability of functional electric stimulation applications to perform repetitive, nonisometric contractions in subjects with SCI. [Copyright &y& Elsevier]

Abstract: Gait dysfunctions are highly prevalent in individuals post-stroke and affect multiple lower extremity joints. Recent evidence suggests that treadmill walking at faster than self-selected speeds can help improve post-stroke gait impairments. Also, the combination of functional electrical stimulation (FES) and treadmill training has emerged as a promising post-stroke gait rehabilitation intervention. However, the differential effects of combining FES with treadmill walking at the fast versus a slower, self-selected speed have not been compared previously. In this study, we compared the immediate effects on gait while post-stroke individuals walked on a treadmill at their self-selected speed without FES (SS), at the SS speed with FES (SS–FES), at the fastest speed they are capable of attaining (FAST), and at the FAST speed with FES (FAST–FES). During SS–FES and FAST–FES, FES was delivered to paretic ankle plantarflexors during terminal stance and to paretic dorsiflexors during swing phase. Our results showed improvements in peak anterior ground reaction force (AGRF) and trailing limb angle during walking at FAST versus SS. FAST–FES versus SS–FES resulted in greater peak AGRF, trailing limb angle, and swing phase knee flexion. FAST–FES resulted in further increase in peak AGRF compared to FAST. We posit that the enhancement of multiple aspects of post-stroke gait during FAST–FES suggest that FAST–FES may have potential as a post-stroke gait rehabilitation intervention. [Copyright &y& Elsevier]