Physiologic decrease of single thenar motor units in the F-response in stroke patients

Adaptation in the spinal cord after stroke: Implications for restoring cortical control over the final common pathway

Control of voluntary movement is predicated on integration between circuits in the brain and spinal cord. Although damage is often restricted to supraspinal or spinal circuits in cases of neurological injury, both spinal motor neurons and axons linking these cells to the cortical origins of descending motor commands begin showing changes soon after the brain is injured by stroke. The concept of 'transneuronal degeneration' is not new and has been documented in histological, imaging and electrophysiological studies dating back over a century. Taken together, evidence from these studies agrees more with a system attempting to survive rather than one passively surrendering to degeneration. There tends to be at least some preservation of fibres at the brainstem origin and along the spinal course of the descending white matter tracts, even in severe cases. Myelin-associated proteins are observed in the spinal cord years after stroke onset. Spinal motor neurons remain morphometrically unaltered. Skeletal muscle fibres once innervated by neurons that lose their source of trophic input receive collaterals from adjacent neurons, causing spinal motor units to consolidate and increase in size. Although some level of excitability within the distributed brain network mediating voluntary movement is needed to facilitate recovery, minimal structural connectivity between cortical and spinal motor neurons can support meaningful distal limb function. Restoring access to the final common pathway via the descending input that remains in the spinal cord therefore represents a viable target for directed plasticity, particularly in light of recent advances in rehabilitation medicine.

Compound muscle action potential (CMAP) scan examination of paretic and contralateral muscles reveals motor unit alterations after stroke

This study presents a novel compound muscle action potential (CMAP) examination of motor unit changes in paretic muscle post stroke. CMAP scan of the first dorsal interosseous (FDI) muscle was performed bilaterally in 16 chronic stroke subjects. Various parameters were derived from the CMAP scan to examine paretic muscle changes, including CMAP amplitude, D50, step index (STEPIX) and amplitude index (AMPIX). A significant decrease in CMAP amplitude and STEPIX was observed in paretic muscles compared with contralateral muscles (CMAP amplitude: paretic (9.0±0.5) mV, contralateral (11.3±0.9) mV, P=0.024; STEPIX: paretic 101.2±7.6, contralateral 121.9±6.5, P=0.020). No significant difference in D50 and AMPIX was observed between the paretic and contralateral sides (P>0.05). The findings revealed complex paretic muscle changes including motor unit degeneration, muscle fiber denervation, reinnervation and atrophy, providing useful insights to help understand neuromuscular mechanisms associated with weakness and other functional deterioration post stroke. The CMAP scan experimental protocols and the applied processing methods are noninvasive, convenient, and automated, offering practical benefits for clinical application.

Motor Unit Number Estimation in Spastic Biceps Brachii Muscles of Chronic Stroke Survivors Before and After BoNT Injection

OBJECTIVE

The study aims to characterize the motor unit (MU) loss in spastic biceps brachii muscle (BBM) of chronic stroke survivors before and after botulinum neurotoxin (BoNT) injection.

METHODS

High-density weighted average (HDWA) motor unit number estimation (MUNE) was employed to estimate the number of functioning motor units of BBMs of eight chronic stroke survivors 1-week before (1st visit) and 3-week after (2nd visit) BoNT injection based on the surface electromyography (sEMG) signals recorded during voluntary contraction and supramaximal electrical stimulation.

RESULT

Significant lower MUNE was estimated from the spastic BBMs compared to the non-spastic MUNEs during two visits. A surprisingly higher MUNE was obtained from the spastic side during the 2nd visit after BoNT injection.

CONCLUSIONS

The HDWA MUNE technique can be employed to characterize the motor unit loss in spastic muscle caused by upper motor neuro lesions at contraction level up to 30% MVC, but may fail to detect the MU loss caused by the chemodenervation effect of BoNT due to the non-uniform denervation of small and large size MUs.

SIGNIFICANCE

This study presents the first effort to evaluate the applicability of HDWA MUNE technique to characterize the MU loss in the spastic muscle following stroke and the subsequent BoNT injection for the treatment of post-stroke spasticity. The finding of this study suggests that HDWA MUNE can be a sensitive approach to detect the MU loss in spastic muscles after stroke, but the large inter-subject MUNE variability after the BoNT injection should be interpreted with caution.

Automatic detection of F-waves and F-MUNE in Two Types of Motor Neuron Diseases

INTRODUCTION/AIMS

Motor unit number estimation by F-waves (F-MUNE) is an uncommonly used MUNE technique. The aim of this study was to analyze the sensitivity of F-MUNE values elicited with newly developed software in motor neuron diseases.

METHODS

F-waves were recorded by 300 submaximal stimuli from abductor digiti minimi (ADM) and abductor pollicis brevis (APB) muscles of 35 patients with amyotrophic lateral sclerosis, 18 with previous poliomyelitis, and 20 controls. The software extracted the surface motor unit action potentials (sMUAP) and calculated the F-MUNE values. CMAP Scans were also recorded to obtain step% and MScanFit.

RESULTS

sMUAP amplitudes were higher and F-MUNE values were lower in both muscles of the patients than in controls. F-MUNE values were able to distinguish the patients from controls. Significant correlations were found between F-MUNE and MScanFit in patient groups.

DISCUSSION

The new F-MUNE software gave promising results in revealing motor unit loss caused by motor neuron diseases.

Model-Based Sensitivity Analysis of EMG Clustering Index With Respect to Motor Unit Properties: Investigating Post-Stroke FDI Muscle

The objective of this study is to explore the diagnostic decision and sensitivity of the surface electromyogram (EMG) clustering index (CI) with respect to post-stroke motor unit (MU) alterations through a simulation approach by the existing motor neuron pool model and surface EMG model. In the simulation analysis, three patterns of diagnostic decisions were presented in 24 groups representing eight types in three degrees of MU alterations. Specifically, the CI decision exhibited an abnormally increased pattern for five types, an abnormally decreased pattern for two types, and an invariant pattern for one type. Furthermore, the CI diagnostic decision was found to be highly sensitive to three types because a 50% degree of alteration in these types resulted in a distinct deviation of 2.5 in the CI Z-score. The mixed CI patterns were confirmed in experimental data collected from the paretic muscles of 14 subjects with stroke, as compared to the healthy muscles of 10 control subjects. Given the simulation results as a guideline, the CI diagnostic decision could be interpreted from general neural or muscular changes into specific MU changes (in eight types). This can further promote clinical applications of the convenient surface EMG tool in examining and monitoring paretic muscle changes toward customized stroke rehabilitation.

Electrodiagnostic and nerve ultrasonographic features in upper limb spasticity: an observational study

To better understand the effects of spasticity on peripheral nerves, we evaluated the electrodiagnostic and nerve ultrasonographic features of the median and ulnar nerves in adults with upper limb spasticity. Twenty chronic stroke patients with spastic hemiparesis underwent nerve conduction study and nerve ultrasonography of the median and ulnar nerves at both upper limbs. Affected versus unaffected upper limb comparisons showed significant differences in the median and ulnar nerve distal motor latencies, compound muscle action potentials and F-wave minimal latencies. Furthermore, we observed a significantly greater median nerve crosssectional area at the elbow of the affected upper limb compared with the unaffected one. Our findings confirmed electrodiagnostic asymmetries and nerve ultrasonographic abnormalities in the affected versus the unaffected upper limb after stroke. Slight changes in lower motor neuron activity and spasticity might contribute to these alterations.

Assessing Hand Muscle Structural Modifications in Chronic Stroke

The purpose of the study is to assess poststroke muscle structural alterations by examining muscular electrical conductivity and inherent electrophysiological properties. In particular, muscle impedance and compound muscle action potentials (CMAP) were measured from the hypothenar muscle bilaterally using the electrical impedance myography and the electrophysiological techniques, respectively. Significant changes of muscle impedance were observed in the paretic muscle compared with the contralateral side (resistance: paretic: 27.54 ± 0.97 Ω, contralateral: 25.46 ± 0.91 Ω, p < 0.05; phase angle: paretic: 8.81 ± 0.61°, contralateral: 10.79 ± 0.69°, p < 0.05). In addition, impedance changes correlated moderately with the CMAP amplitude in the paretic hand (phase angle: r = 0.66, p < 0.05; reactance: r = 0.58, p < 0.05). The study discloses significant muscle rearrangements as a result of fiber loss or atrophy, fat infiltration or impaired membrane integrity in chronic stroke.

Physical treatment interventions for managing spasticity after stroke

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

Bilateral changes in muscle architecture of physically active people with chronic stroke: A quantitative muscle ultrasound study

OBJECTIVE

Changes in muscle architecture after stroke are usually assessed by investigating inter-limb differences. As a result bilateral changes of muscle architecture might be missed. Our aim was to investigate whether bilateral architectural changes in skeletal muscle can be detected in chronic, physically active stroke patients using quantitative muscle ultrasound (QMUS).

METHODS

Twenty-eight patients (mean time since stroke 5.2years, median Brunnström stage 4) were recruited. QMUS images were obtained bilaterally from 2 arm and 4 leg muscles. Corrected echogenicity (muscle ultrasound grayvalue) and muscle thickness were compared to reference values obtained from healthy subjects. Correlations of muscle changes with demographic, clinical and neurophysiological characteristics were explored.

RESULTS

Out of 6 muscles, a significant increase in mean echogenicity was found in 4 paretic and 3 non-paretic side muscles. Significant decreases in mean muscle thickness were found in 2 paretic side muscles and 1 non-paretic side muscle. Echogenicity of the medial gastrocnemius correlated moderately with walking speed (inversely) and time since stroke.

CONCLUSIONS

This study showed that QMUS is a feasible technique to investigate architectural changes in skeletal muscles in the chronic phase of stroke and that abnormalities can be found in muscles on both the hemiparetic and non-paretic side.

SIGNIFICANCE

Intriguing data on bilateral changes in muscles of people with stroke is presented. Directions for future research are provided.

Asynchronization in Changes of Electrophysiology and Pathology of Spinal Cord Motor Neurons in Rats Following Middle Cerebral Artery Occlusion

Background:

Motor dysfunction is common in stroke patients. Clinical electrophysiological studies suggest that transsynaptic degeneration occurred in the lower motor neurons, while pathological evidence is lacked. This study aimed to combine the electrophysiological and pathological results to prove the existence of transsynaptic degeneration in the motor system after stroke.

Methods:

Modified neurologic severity score, electrophysiological, and pathological assessments were evaluated in rats before middle cerebral artery occlusion (MCAO), and at 24 hours, 7 days, and 14 days after MCAO. Paired and independent-sample t-tests were applied to assess the changes of electrophysiological and pathological data.

Results:

Compound motor action potential amplitude in the paretic side was significantly lower than the nonparetic side at both 24 hours (61.9 ± 10.4 vs. 66.6 ± 8.9, P < 0.05) and 7 days (60.9 ± 8.4 vs. 67.3 ± 9.6, P < 0.05) after MCAO. Motor unit number estimation of the paretic side was significantly less than the nonparetic side (379.0 ± 84.6 vs. 445.0 ± 89.5, P < 0.05) at 7 days after MCAO. Until 14 days after stroke, the pathological loss of motor neurons was detected. Motor neurons in 14-day MCAO group were significantly decreased, compared with control group (5.3 ± 0.7 vs. 7.3 ± 1.8, P < 0.05).

Conclusions:

Both electrophysiological and pathological studies showed transsynaptic degeneration after stroke. This study identified the asynchronization in changes of electrophysiology and pathology. The abnormal physiological changes and function impairment can be detected in the early stage and recovered quickly, while the pathological loss of motor neuron can be detected only in a later stage.

Application of the F-Response for Estimating Motor Unit Number and Amplitude Distribution in Hand Muscles of Stroke Survivors

The F-response was used in this study to assess changes in the first dorsal interosseous (FDI) muscle after a hemispheric stroke. The number of motor units and their sizes were estimated bilaterally in 12 stroke survivors by recording both the compound muscle action potential (CMAP) and F wave responses. These F waves were induced by applying a large number of electrical stimuli to the ulnar nerve. The amplitude distribution of individual motor unit action potentials (MUAPs) was also compared between paretic and contralateral muscles. When averaged across all the subjects, a significantly lower motor unit number estimate was obtained for the paretic FDI muscle ( 88 ±13) compared with the contralateral side ( 139 ±11) ( ). Pooled surface MUAP amplitude analysis demonstrated a right-skewed distribution for both paretic (kurtosis 3.0) and contralateral (kurtosis 8.52) muscles. When normalized to each individual muscle's CMAP, the surface MUAP amplitude ranged from 0.22% to 4.94% (median 1.17%) of CMAP amplitude for the paretic muscle, and from 0.13% to 3.2% (median 0.62%) of CMAP amplitude for the contralateral muscle. A significant difference in MUAP outliers was also observed between the paretic and contralateral muscles. The findings of this study suggest significant motor unit loss and muscle structural reorganization after stroke.

Effect of Motor Imagery on the F-Wave Parameters in Hemiparetic Stroke Survivors

Objective

To assess the effect of motor imagery, as a rehabilitation method in stroke, on F-wave parameters that undergo changes during upper motor neuron involvement.

Methods

Twenty-one fully conscious hemiparetic stroke survivors with a completely plegic hand (power 0/5) and a minimum interval of 72 hours since stroke were recruited into this study. The mean F-wave latency, amplitude, and persistence in the median and ulnar nerves were measured in both the affected and non-affected sides at rest and in the paretic hand during a mental task. Comparison was made between data from the affected hand and the non-affected hand as well as between data from the affected hand at baseline and during motor imagery.

Results

Patients had significantly different F-wave persistence between the affected and non-affected sides (paired t-test, p<0.001). Motor imagery could improve F-wave persistence in both the investigated nerves (paired t-test, p=0.01 for ulnar nerve and p<0.001 for median nerve) and F-response amplitude in the median nerve (paired t-test, p=0.01) of the affected limb.

Conclusion

The amplitude and persistence of F-wave were improved during motor imagery, representing F-wave facilitation. This result suggests that motor imagery can restore motor neuron excitability, which is depressed after stroke.

Motor unit number estimation and quantitative needle electromyography in stroke patients

OBJECTIVE

To evaluate the effect of upper motor neuron damage upon motor units' function by means of two separate and supplementary electrophysiological methods.

METHODS

The abductor digiti minimi muscle of the non-paretic and the paretic side was studied in forty-six stroke patients with (a) motor unit number estimation (MUNE) - adapted multiple point stimulation method and (b) computerized quantitative needle electromyography (EMG) assessing the configuration of voluntary recruited motor unit potentials. Main outcome comparisons were focused on differences between non-paretic and paretic side.

RESULTS

On the affected hands mean MUNE value was significantly lower and mean area of the surface recorded single motor unit potentials was significantly larger than the corresponding ones on the non-paretic hands. EMG findings did not reveal remarkable differences between the two sides. Neither severity nor chronicity of stroke was related to MUNE or EMG parameters.

DISCUSSION

MUNE results, which suggested reduced motor unit numbers in stroke patients, in conjunction with the normal EMG features in these same muscles has given rise to different interpretations. In a clinical setting, reinnervation type changes in the EMG similar to that occurring in neuronopathies or axonal neuropathies should not be expected in muscles with central neurogenic lesion.

Single motor unit firing rate after stroke is higher on the less-affected side during stable low-level voluntary contractions

Muscle weakness is the most common outcome after stroke and a leading cause of adult-acquired motor disability. Single motor unit properties provide insight into the mechanisms of post-stroke motor impairment. Motor units on the more-affected side are reported to have lower peak firing rates, reduced discharge variability and a more compressed dynamic range than healthy subjects. The activity of 169 motor units was discriminated from surface electromyography in 28 stroke patients during sustained voluntary contractions 10% of maximal and compared to 110 units recorded in 16 healthy subjects. Motor units were recorded in three series: ankle dorsiflexion, wrist flexion and elbow flexion. Mean firing rates after stroke were significantly lower on the more-affected than the less-affected side (p < 0.001) with no differences between dominant and non-dominant sides for healthy subjects. When data were combined, firing rates on the less-affected side were significantly higher than those either on the more-affected side or healthy subjects (p < 0.001). Motor unit mean firing rate was higher in the upper-limb than the lower-limb (p < 0.05). The coefficient of variation of motor unit discharge rate was lower for motor units after stroke compared to controls for wrist flexion (p < 0.05) but not ankle dorsiflexion. However the dynamic range of motor units was compressed only for motor units on the more-affected side during wrist flexion. Our results show that the pathological change in motor unit firing rate occurs on the less-affected side after stroke and not the more-affected side as previously reported, and suggest that motor unit behavior recorded in a single muscle after stroke cannot be generalized to muscles acting on other joints even within the same limb. These data emphasize that the less-affected side does not provide a valid control for physiological studies on the more-affected side after stroke and that both sides should be compared to data from age- and sex-matched healthy subjects.

Association of seat height and arm position on the five times sit-to-stand test times of stroke survivors

Objectives. To investigate (1) the association of seat height and (2) the association of arm position on the five times sit-to-stand test (FTSTS) times of individuals with stroke. Design. A cross-sectional study. Setting. University-based rehabilitation centre. Subjects. Patients (n = 43) with chronic stroke. Methods. The times in completing the FTSTS with different seat height (85%, 100%, and 115% knee height) and arm positions (arms across chest, hands on thighs). Results. FTSTS times were significantly different between 85% and 100% seat heights, and between the 85% and 115% seat heights in both arm positions. However, there was no significant difference between the FTSTS times with the two arm positions at any seat height tested. Conclusion. Seat heights lower than the knee height result in longer FTSTS times, whereas arms positions did not significantly affect the FTSTS times.

A simulation-based analysis of motor unit number index (MUNIX) technique using motoneuron pool and surface electromyogram models

Motor unit number index (MUNIX) measurement has recently achieved increasing attention as a tool to evaluate the progression of motoneuron diseases. In our current study, the sensitivity of the MUNIX technique to changes in motoneuron and muscle properties was explored by a simulation approach utilizing variations on published motoneuron pool and surface electromyogram (EMG) models. Our simulation results indicate that, when keeping motoneuron pool and muscle parameters unchanged and varying the input motor unit numbers to the model, then MUNIX estimates can appropriately characterize changes in motor unit numbers. Such MUNIX estimates are not sensitive to different motor unit recruitment and rate coding strategies used in the model. Furthermore, alterations in motor unit control properties do not have a significant effect on the MUNIX estimates. Neither adjustment of the motor unit recruitment range nor reduction of the motor unit firing rates jeopardizes the MUNIX estimates. The MUNIX estimates closely correlate with the maximum M-wave amplitude. However, if we reduce the amplitude of each motor unit action potential rather than simply reduce motor unit number, then MUNIX estimates substantially underestimate the motor unit numbers in the muscle. These findings suggest that the current MUNIX definition is most suitable for motoneuron diseases that demonstrate secondary evidence of muscle fiber reinnervation. In this regard, when MUNIX is applied, it is of much importance to examine a parallel measurement of motor unit size index (MUSIX), defined as the ratio of the maximum M-wave amplitude to the MUNIX. However, there are potential limitations in the application of the MUNIX methods in atrophied muscle, where it is unclear whether the atrophy is accompanied by loss of motor units or loss of muscle fiber size.

Translating preclinical approaches into human application

In recent decades, several novel approaches of spinal cord repair have revealed promising findings in animal models. However, for a successful translation of these into a clinical trial in humans the specific conditions pertaining to human spinal cord injuries (SCI) have to be appreciated. Firstly, transection of the spinal cord is commonly applied in animal models, whereas spinal cord contusion is the predominant type of injury in humans, and generally leads to more extensive injury in two to three spinal cord segments. Secondly, the quadrupedal organization of locomotion in animals and the more complex autonomic functions in humans challenge the translation of animal behavior into recovery from human SCI. Thirdly, so far, no adequate animal model has been developed to resemble spastic movement disorder in human SCI. Fourthly, the extensive damage to spinal motor neurons and nerve roots in human cervical and thoracolumbar in spine trauma is but little addressed in current translational studies. This damage has direct implications for rehabilitation and repair strategies. Fifthly, there is increasing evidence for a neuronal dysfunction below the level of the lesion in chronic complete SCI. The relevance of this dysfunction for a regeneration-inducing treatment needs to be investigated. Lastly, an approach to facilitate an appropriate reconnection of regenerating tract fibers by functional training in the postacute stage has yet to be confirmed.

Spinal reflex properties in the long term after stroke

In the long term after stroke, secondary functional deterioration may be observed while patients also get older. Possible underlying mechanisms are largely unknown. We aimed to assess neuromuscular degeneration represented by alterations in peripheral reflex loop characteristics as a function of follow-up time after stroke, controlled for age. Twenty-one stroke survivors within a small age range (62-67 years) but large variance in follow-up time after stroke (1-15 years) and both five age matched (59-62 years) and young subjects (28-36 years) participated. Short and long latency reflexes evoked by ramp and hold stretches were identified from EMG traces of the m. flexor carpi radialis. Short latency reflex onset time was not enhanced (mean difference 1.6ms compared to age matched controls) and did not relate to follow-up time after stroke (p=0.81). Young controls showed significantly lower reflex delay times (mean difference 7.2ms with respect to older subjects, p=0.009). No evidence was found for peripheral neuromuscular deterioration as a function of follow up time after stroke. Functional deterioration as a result of ageing of stroke patients that may interact with post stroke follow-up time is of further interest.

The effects of notch filtering on electrically evoked myoelectric signals and associated motor unit index estimates

Background

Notch filtering is the most commonly used technique for suppression of power line and harmonic interference that often contaminate surface electromyogram (EMG) signals. Notch filters are routinely included in EMG recording instrumentation, and are used very often during clinical recording sessions. The objective of this study was to quantitatively assess the effects of notch filtering on electrically evoked myoelectric signals and on the related motor unit index measurements.

Methods

The study was primarily based on an experimental comparison of M wave recordings and index estimates of motor unit number and size, with the notch filter function of the EMG machine (Sierra Wave EMG system, Cadwell Lab Inc, Kennewick, WA, USA) turned on and off, respectively. The comparison was implemented in the first dorsal interosseous (FDI) muscle from the dominant hand of 15 neurologically intact subjects and bilaterally in 15 hemiparetic stroke subjects.

Results

On average, for intact subjects, the maximum M wave amplitude and the motor unit number index (MUNIX) estimate were reduced by approximately 22% and 18%, respectively, with application of the built-in notch filter function in the EMG machine. This trend held true when examining the paretic and contralateral muscles of the stroke subjects. With the notch filter on vs. off, across stroke subjects, we observed a significant decrease in both maximum M wave amplitude and MUNIX values in the paretic muscles, as compared with the contralateral muscles. However, similar reduction ratios were obtained for both maximum M wave amplitude and MUNIX estimate. Across muscles of both intact and stroke subjects, it was observed that notch filtering does not have significant effects on motor unit size index (MUSIX) estimate. No significant difference was found in MUSIX values between the paretic and contralateral muscles of the stroke subjects.

Conclusions

The notch filter function built in the EMG machine may significantly reduce the M wave amplitude and the MUNIX measurement. However, the notch filtering does not jeopardize the evaluation of the reduction ratio in maximum M wave amplitude and MUNIX estimate of the paretic muscles of stroke subjects when compared with the contralateral muscles.

Motor unit number reductions in paretic muscles of stroke survivors

The objective of this study is to assess whether there is evidence of spinal motoneuron loss in paretic muscles of stroke survivors, using an index measurement called motor unit number index (MUNIX). MUNIX, a recently developed novel neurophysiological technique, provides an index proportional to the number of motor units in a muscle, but not necessarily an accurate absolute count. The MUNIX technique was applied to the first dorsal interosseous (FDI) muscle bilaterally in nine stroke subjects. The area and power of the maximum M-wave and the interference pattern electromyogram (EMG) at different contraction levels were used to calculate the MUNIX. A motor unit size index (MUSizeIndex) was also calculated using maximum M-wave recording and the MUNIX values. We observed a significant decrease in both maximum M-wave amplitude and MUNIX values in the paretic FDI muscles, as compared with the contralateral muscles. Across all subjects, the maximum M-wave amplitude was 6.4 ± 2.3 mV for the paretic muscles and 9.7 ± 2.0 mV for the contralateral muscles (p < 0.001). These measurements, in combination with voluntary EMG recordings, resulted in the MUNIX value of 109 ± 53 for the paretic muscles, much lower than the MUNIX value of 153 ± 38 for the contralateral muscles ( p < 0.01). No significant difference was found in MUSizeIndex values between the paretic and contralateral muscles. However, the range of MUSizeIndex values was slightly wider for paretic muscles (48.8-93.3 μV) than the contralateral muscles (51.7-84.4 μV). The findings from the index measurements provide further evidence of spinal motoneuron loss after a hemispheric brain lesion.

Voluntary breathing influences corticospinal excitability of nonrespiratory finger muscles

The present study aimed to investigate neurophysiologic mechanisms mediating the newly discovered phenomenon of respiratory-motor interactions and to explore its potential clinical application for motor recovery. First, young and healthy subjects were instructed to breathe normally (NORM); to exhale (OUT) or inhale (IN) as fast as possible in a self-paced manner; or to voluntarily hold breath (HOLD). In experiment 1 (n = 14), transcranial magnetic stimulation (TMS) was applied during 10% maximal voluntary contraction (MVC) finger flexion force production or at rest. The motor-evoked potentials (MEPs) were recorded from flexor digitorum superficialis (FDS), extensor digitorum communis (EDC), and abductor digiti minimi (ADM) muscles. Similarly, in experiment 2 (n = 11), electrical stimulation (ES) was applied to FDS or EDC during the described four breathing conditions while subjects maintained 10%MVC of finger flexion or extension and at rest. In the exploratory clinical experiments (experiment 3), four patients with chronic neurological disorders (three strokes, one traumatic brain injury) received a 30-min session of breathing-controlled ES to the impaired EDC. In experiment 1, the EDC MEP magnitudes increased significantly during IN and OUT at both 10%MVC and rest; the FDS MEPs were enhanced only at 10%MVC, whereas the ADM MEP increased only during OUT, compared with NORM for both at rest and 10%MVC. No difference was found between NORM and HOLD for all three muscles. In experiment 2, when FDS was stimulated, force response was enhanced during both IN and OUT, but only at 10%MVC. When EDC was stimulated, force response increased at both 10%MVC and rest, only during IN, but not OUT. The averaged response latency was 83 ms for the finger extensors and 79 ms for the finger flexors. After a 30-min intervention of ES to EDC triggered by forced inspiration in experiment 3, we observed a significant reduction in finger flexor spasticity. The spasticity reduction lasted for ≥ 4 wk in all four patients. TMS and ES data, collectively, support the phenomenon that there is an overall respiration-related enhancement on the motor system, with a strong inspiration-finger extension coupling during voluntary breathing. As such, breathing-controlled electrical stimulation (i.e., stimulation to finger extensors delivered during the voluntary inspiratory phase) could be applied for enhancing finger extension strength and finger flexor spasticity reduction in poststroke patients.

Muscle activation changes during body weight support treadmill training after focal cortical ischemia: A rat hindlimb model

The study used a focal ischemia rat hindlimb model to investigate muscle activity changes during a 10-day body weight support (BWS) treadmill training program. The changes being studied included fatigue effects, EMG burst duration in the gait cycle, and the symmetry of muscle activation between affected and unaffected sides. Intramuscular EMG of medial gastrocnemius (MG) and tibialis anterior (TA) muscles in male Sprague Dawley rats at affected side (n=10) and unaffected side (n=10) were recorded during the treadmill running before a middle cerebral artery occlusion/reperfusion (MCAo/r) surgery and poststroke recovery stage. Behavioral test score and bodyweight were recorded at a daily basis after stroke. The mean power frequency (MPF) of the EMG, EMG burst duration in the gait cycle, and symmetry index between two sides were used for analysis. The drop rate of MPF of MG at the unaffected side increased (P<0.05) at poststroke day 2 and it generally decreased along the poststroke training days and almost returned to baseline value at poststroke day 6. Symmetry index of MG and TA showed a large imbalance right after stroke and tended to return to normal. Our findings of the MPF drop after stroke might indicate fatigue effects due to the compensation loading share of the ipsilateral side muscle and the increase of the symmetry index reflects abnormal gait pattern after the onset of stroke. The recovery rate after stroke could be investigated with EMG parameters together with the behavioral score, and both were improved during and after the BWS treadmill training.

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.

Behavior of spinal neurons deprived of supraspinal input

This Review discusses the spinal neuronal changes that occur after a complete spinal cord injury (SCI) in humans. Early after an SCI, neither locomotor nor spinal reflex activity can be evoked. Once spinal shock has resolved, locomotor activity and an early spinal reflex component reappear in response to appropriate peripheral afferent input. In the subsequent 4-8 months, clinical signs of spasticity appear, largely as a result of non-neuronal (for example, muscular) changes, whereas locomotor and spinal reflex activity undergo little change. At 9-12 months, the electromyographic amplitude in the leg muscles during assisted locomotion declines, accompanied by a decrease in the amplitude of the early spinal reflex component and an increase in the amplitude of a late spinal reflex component. This exhaustion of locomotor activity also occurs in nonambulatory patients with incomplete SCI. Neuronal dysfunction is fully established 1 year after the injury without further alterations in subsequent years. In chronic SCI, the absence of input from supraspinal sources has been suggested to lead to degradation of neuronal function below the level of the lesion or, alternatively, a predominance of inhibitory signaling to the locomotor pattern generator. Appropriate training and/or provision of afferent input to spinal neurons might help to prevent neuronal dysfunction in chronic SCI.

Changes in muscle fiber density following a stroke

OBJECTIVES

Previous studies have revealed a selective functional loss of the large, high-threshold motor units in the paretic muscles after lesion of the upper motor neuron. We set out to study the degree and the time course of the reorganization of the motor units following a stroke.

METHODS

Examinations were performed on 59 patients with a unilateral ischemic stroke in the territory of the middle cerebral artery, and on 42 healthy controls. The duration of hemiparesis ranged from 2 weeks to 48 months. The fiber density (FD) in the abductor digiti minimi muscle was determined by means of single-fiber electromyography on both the hemiparetic and the unaffected side in the patients, and unilaterally in the control subjects.

RESULTS

The FD was increased on the hemiparetic side relative to the unaffected side and the control group. This change correlated with the severity of the clinical signs. The FD increased during the first 10 months following the stroke and subsequently remained stable.

CONCLUSIONS

The process of reinnervation in the muscles takes place in the acute phase after stroke. These changes are related to the severity of the symptoms.

SIGNIFICANCE

Our findings suggest that trans-synaptic degeneration of the spinal motor neurons occurs shortly after the lesion of the upper motor neurons.

New mathematical approach for approximating the baseline of F-waves using spreadsheet software

OBJECTIVE

The aim of this study was to see if curved baselines of F-waves could be mathematically approximated with universal spreadsheet software.

METHODS

The subjects were 3 healthy persons and 3 patients with cervical myelopathy. Supramaximal electrical stimuli were applied 200 times to the median nerve at the wrist. Compound muscle action potentials (CMAPs) of the abductor pollicis brevis were recorded. To make polynomial approximation equations that represent latter part of the M-waves, records without F-waves were analyzed.

RESULTS

There were 193 CMAPs without F-waves out of all 1,200 records. Polynomial equations were made for each record. Determinant coefficients for all the approximation equations were greater than 0.998, and the overall standard deviation of the difference between original data and approximated value was 3.05 microV.

CONCLUSIONS

Curved baselines of F-waves were represented by approximation curves. Baselines of the F-waves could be approximated as flat lines by subtracting calculated values from the original data.

SIGNIFICANCE

This method was useful for analyzing waveforms of F-waves.

Large motor units are selectively affected following a stroke

OBJECTIVE

Previous studies have revealed a loss of functioning motor units in stroke patients. However, it remained unclear whether the motor units are affected randomly or in some specific pattern. We assessed whether there is a selective loss of the large (high recruitment threshold) or the small (low recruitment threshold) motor units following a stroke.

METHODS

Forty-five stroke patients and 40 healthy controls participated in the study. Macro-EMG was recorded from the abductor digiti minimi muscle at two levels of force output (low and high). The median macro motor unit potential (macro-MUP) amplitude on the paretic side was compared with those on the unaffected side and in the controls.

RESULTS

In the control group and on the unaffected side, the macro-MUPs were significantly larger at the high force output than at the low one. However, on the paretic side the macro-MUPs at the high force output had the same amplitude as those recorded at the low force output. These changes correlated with the severity of the paresis.

CONCLUSIONS

Following a stroke, there is a selective functional loss of the large, high-threshold motor units. These changes are related to the severity of the symptoms.

SIGNIFICANCE

Our findings furnish further insight into the pathophysiology of the motor deficit following a stroke.

Supratentorial ischemic stroke: more than an upper motor neuron disorder

The primary goal of this study was to identify secondary functional changes in the peripheral motor units of the paretic upper extremity (UE) in patients with severe ischemic stroke and to determine how these changes develop during the first weeks after stroke. An inception cohort of 27 consecutive patients with an acute ischemic supratentorial stroke and an initial UE paralysis was compared with 10 healthy control subjects. The ulnar nerve was electrically stimulated proximal to the wrist and electromyographic recordings were obtained from the abductor digiti minimi muscle. Hemiparetic side mean values of the compound muscle action potential (CMAP) 1 and 3 weeks after stroke were compared with the nonparetic side and with CMAP values obtained from healthy control subjects. The mean CMAP amplitude in patients was significantly lower on the paretic side compared with the nonparetic side and with control subjects. Decrease in CMAP amplitude was observed in more than half of the stroke patients, sometimes as early as 4 days after stroke, and persisted in most cases. Whenever present, it was accompanied by absence of motor recovery at that specific time after stroke. Decreased CMAP amplitude in the abductor digiti minimi muscle can be seen already in the very acute phases after stroke unrelated to peripheral neuropathy, radiculopathy, or plexopathy, and it is accompanied by absence of UMN recovery. This knowledge is important for interpreting electrophysiological data in stroke patients.

The correlation between F-wave motor unit number estimation (F-MUNE) and functional recovery in stroke patients

The aim of this study was to follow up the changes in the number of motor units according to the Brunnstrom stage through a motor unit number estimation of the Fwave (F-MUNE) after a stroke, and to identify the functional significance of F-MUNE. Twenty-five patients (15 men, 10 women) with a first unilateral stroke were recruited. The maximal M-potential was evoked by the supramaximal stimulation of the median nerve at the wrist, and the maximal stimulation intensity was determined on both hemiplegic and unaffected hands. The reproducible all-or-none F-wave was evoked in 30% of the maximal stimulation intensity and was constantly stimulated at that level. The prototypes of the F-wave were chosen, and the values of F-MUNE were calculated by dividing the amplitude of the maximal M-potential by the mean amplitude of the F-prototype. The changes in F-MUNE were compared according to the progression of the Brunnstrom stage and correlated with those of the functional scales. The mean motor unit numbers decreased significantly in the hemiplegic side compared with the unaffected side. According to the progression of the Brunnstrom stage, the values of F-MUNE were reduced significantly by increasing the amplitude and recruitment of the F-prototype, and the functional scores also improved. These results show that the F-MUNE equation did not show a functional recovery related increase in stroke patients.

Strengthening interventions increase strength and improve activity after stroke: a systematic review

QUESTION

Is strength training after stroke effective (ie, does it increase strength), is it harmful (ie, does it increase spasticity), and is it worthwhile (ie, does it improve activity)?

DESIGN

Systematic review with meta-analysis of randomised trials.

PARTICIPANTS

Stroke participants were categorised as (i) acute, very weak, (ii) acute, weak, (iii) chronic, very weak, or (iv) chronic, weak.

INTERVENTION

Strengthening interventions were defined as interventions that involved attempts at repetitive, effortful muscle contractions and included biofeedback, electrical stimulation, muscle re-education, progressive resistance exercise, and mental practice.

OUTCOME MEASURES

Strength was measured as continuous measures of force or torque or ordinal measures such as manual muscle tests. Spasticity was measured using the modified Ashworth Scale, a custom made scale, or the Pendulum Test. Activity was measured directly, eg, 10-m Walk Test, or the Box and Block Test, or with scales that measured dependence such as the Barthel Index.

RESULTS

21 trials were identified and 15 had data that could be included in a meta-analysis. Effect sizes were calculated as standardised mean differences since various muscles were studied and different outcome measures were used. Across all stroke participants, strengthening interventions had a small positive effect on both strength (SMD 0.33, 95% CI 0.13 to 0.54) and activity (SMD 0.32, 95% CI 0.11 to 0.53). There was very little effect on spasticity (SMD -0.13, 95% CI -0.75 to 0.50).

CONCLUSION

Strengthening interventions increase strength, improve activity, and do not increase spasticity. These findings suggest that strengthening programs should be part of rehabilitation after stroke.

Updating motor unit number estimation (MUNE)

Motor unit number estimation (MUNE) is a unique electrophysiologic technique that can provide a numeric estimate of the number of axons innervating a muscle or group of muscles. The first technique was first described in 1971, and since then different techniques have been developed to address specific methodologic issues. The field was reviewed in this journal in 2001, and this update covers new information and uses of MUNE over the past five years. These include models of muscles that allow evaluation of MUNE techniques and comparisons between techniques. There have been further investigations of specific technical aspects of MUNE. Modifications to MUNE techniques have been offered that permit more rapid acquisition of data. MUNE has been used in clinical situations to elucidate the pathophysiology features of axonal loss in a number of disorders. There is now more experience with MUNE as endpoint measures in clinical trials.

Firing properties of motor units during fatigue in subjects after stroke

The purpose of this work was to investigate the electromyographic (EMG) fatigue representations in muscles of subjects after stroke at the level of motor unit, based on the analysis of mean power frequency (MPF) in the power density spectrum (PDS) for intramuscular EMG and our previous modeling and experiment studies on the neuromuscular transmission failure (NTF). NTF due to the local muscular fatigue had been captured in motor unit signals from healthy subjects during a submaximal fatigue contraction previously. In this study, the EMG signals for the biceps brachii muscles were collected by needle electrodes from the affected and unaffected arms of six hemiplegic subjects after stroke, and from the dominated arm of six healthy subjects during a full maximum voluntary contraction (MVC) and a subsequent 20% MVC. The MPF of EMG trials detected intramuscularly during the full and 20% MVCs, and the parameters of motor unit action potential trains (MUAPTs) during 20% MVC were analyzed in three groups: the normal (from healthy subjects), unaffected (from subjects after stroke), and affected (from subjects after stroke). It was found that during the full MVC the MPFs of the normal and unaffected groups decreased more than the affected when monitored by a moving time window of 2 s. The comparison on the overall MPF during the full MVC for these three groups over the whole time course of the EMG signal (18 s) were: the affected overall MPF was higher than the unaffected (P < 0.05); and the unaffected overall MPF was larger than the normal (P < 0.05). However, no significant decrease in MPF was found for these three groups during 20% MVC. The NTF was captured in most MUAPTs in the groups of the normal and unaffected rather than in the affected group, symbolized by the lowered rates of change (RCs) of firing rate (FR) (P < 0.05), more MUAPTs with positive RCs of maximum oscillation (MO) in MUAPT power density spectra (P < 0.05), and the significant higher RCs of minimum inter-pulse interval (MINI) (P < 0.05) in the normal and unaffected compared to the affected group. Enhanced neural drives to the motor units of the unaffected and affected groups were observed during 20% MVC, which possibly came from the bilateral neural inputs due to the disinhibition of the ipsilateral projections in subjects after stroke. For identifying the fatigue associated with NTF, the motor unit firing parameters, FR, MINI, and MO, were more sensitive than the MPF. The results obtained in this work provided a further understanding on the EMG of the fatigue processes in paretic and non-paretic muscles during voluntary contractions.

Joint-Angle–Dependent Neuromuscular Dysfunctions at the Wrist in Persons After Stroke

OBJECTIVE

To evaluate the joint-angle-dependent neuromuscular functions at the affected wrist in hemiplegic subjects after stroke while doing isometric maximal voluntary wrist flexion and extension across different wrist angles.

DESIGN

We investigated torques during isometric maximal voluntary wrist flexions and extensions at 8 different wrist angles, ranging from -45 degrees to 60 degrees. We used the associated electromyographic activities of 2 agonist and antagonist muscle pairs related to wrist and elbow joints for the analysis of muscular coactivations. We compared the data obtained from poststroke subjects' affected and unaffected sides.

SETTING

A research laboratory in a rehabilitation center.

PARTICIPANTS

Eleven subjects with hemiplegia after stroke with passive range of motion (ROM) in the wrist from -45 degrees to 60 degrees.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Directly measured torques, torques after normalization during maximal isometric wrist contractions, and normalized moving average electromyographic signals of each muscle at the tested positions.

RESULTS

The measured torques of the affected wrists were significantly lower than those of the unaffected wrists at all tested angles during wrist flexion and extension (P<.05). The angle-dependent patterns of the normalized torque across the tested wrist angles varied from those of the unaffected wrists (2-way analysis of variance, P<.05). There were decreases in normalized torques during both flexion and extension at the extended positions in the affected group (P<.05). Abnormal cocontractions were found in agonist and antagonist muscle pairs related to wrist and elbow joints, and between the elbow flexor and wrist extensor when subjects did the wrist contractions on the paretic side, especially at the wrist extended positions.

CONCLUSIONS

Wrist muscle weakness was distributed unevenly across the selected wrist ROM on the affected side, as represented by the varied patterns of the normalized torque-angle relationship, compared with the unaffected wrists. There were reductions in the selective control of muscle coactivating synergies both single-jointly and cross-jointly in the impaired nervous system during wrist contractions; the extent of these reductions was also related to the wrist angle configuration.

Electrophysiological signs of changes in motor units after ischaemic stroke

OBJECTIVE

To study changes in motor units on the hemiparetic side, and the relationship between these changes and time after stroke onset and hemiparetic severity.

METHODS

Neurography and concentric needle EMG were performed, and hemiparetic side mean and extreme parameter values were compared with the unaffected side mean and extreme parameter values using non-parametric tests.

RESULTS

The mean M wave amplitude was significantly lower, while the spontaneous activity and the mean number of motor unit potential (MUAP) phases and turns were significantly higher on the hemiparetic side. The outliers above maximum for MUAP duration and amplitude on the hemiparetic side were significantly higher than those on the unaffected side. Correlations were found between the hemiparetic side parameter values and time after stroke onset and hemiparetic severity.

CONCLUSIONS

Axonal or neuronal lesion occurs and collateral reinnervation starts in the acute phase after stroke, while enlarged motor units are found in the chronic state. These changes correlate with hemiparetic severity.

SIGNIFICANCE

This work confirms the controversial concept about lower motor neuron injury with stroke, and provides some information about its time course.

Muscle strength is a determinant of bone mineral content in the hemiparetic upper extremity: implications for stroke rehabilitation

Individuals with stroke have a high incidence of bone fractures and approximately 30% of these fractures occur in the upper extremity. The high risk of falls and the decline in bone and muscle health make the chronic stroke population particularly prone to upper extremity fractures. This was the first study to investigate the bone mineral content (BMC), bone mineral density (BMD), and soft tissue composition of the upper extremities and their relationship to stroke-related impairments in ambulatory individuals with chronic stroke (onset >1 year). Dual-energy X-ray absorptiometry (DXA) was used to acquire total body scans on 56 (22 women) community-dwelling individuals (>or=50 years of age) with chronic stroke. BMC (g) and BMD (g/cm2), lean mass (g), and fat mass (g) for each arm were derived from the total body scans. The paretic upper extremity was evaluated for muscle strength (hand-held dynamometry), impairment of motor function (Fugl-Meyer motor assessment), spasticity (Modified Ashworth Scale), and amount of use of the paretic arm in daily activities (Motor Activity Log). Results showed that the paretic arm had significantly lower BMC (13.8%, P<0.001), BMD (4.5%, P<0.001), and lean mass (9.0%, P<0.001) but higher fat mass (6.3%, P=0.028) than the non-paretic arm. Multiple regression analysis showed that lean mass in the paretic arm, height, and muscle strength were significant predictors (R2=0.810, P<0.001) of the paretic arm BMC. Height, muscle strength, and gender were significant predictors (R2=0.822, P<0.001) of lean mass in the paretic arm. These results highlight the potential of muscle strengthening to promote bone health of the paretic arm in individuals with chronic stroke.

Relationship between ambulatory capacity and cardiorespiratory fitness in chronic stroke: influence of stroke-specific impairments

STUDY OBJECTIVES

To identify the following in individuals with chronic stroke: (1) the relationship between the maximal oxygen consumption (Vo(2)max) during cycle ergometry and the distance covered in the 6-min walk test (6MWT), and (2) the stroke-specific impairments that are important determinants for the 6MWT distance.

DESIGN

Cross-sectional study using a convenience sample.

SETTING

Exercise testing laboratory in a tertiary rehabilitation center.

PARTICIPANTS

Sixty-three older adults (mean age +/- SD, 65.3 +/- 8.7 years) with an average poststroke interval of 5.5 +/- 4.9 years.

INTERVENTION

Not applicable.

MAIN OUTCOME MEASURES

Each subject underwent a maximal cycle ergometer test and a 6MWT. Oxygen consumption (Vo(2)) was measured during both tests. Subjects were also evaluated for Berg balance scale, modified Ashworth scale of spasticity, isometric knee extension strength, and percentage of body fat.

RESULTS

The 6MWT distance had a low correlation with the Vo(2)max (r = 0.402). Balance, knee extension strength, and spasticity were all significant determinants for the 6MWT distance, with balance being the major contributor for the 6MWT distance, accounting for 66.5% of its variance.

CONCLUSIONS

Factors other than the cardiorespiratory status considerably influenced the ambulatory capacity as measured by the 6MWT. The 6MWT distance alone should not be used to indicate cardiorespiratory fitness in individuals with chronic stroke.

Strength Training in Individuals with Stroke

PURPOSE: This paper reviews the mechanisms underlying the inability to generate force in individuals with stroke and summarizes the effects of strength training in these individuals. In addition, a systematic review of studies that have incorporated progressive strengthening interventions in individuals with stroke is presented. SUMMARY OF KEY POINTS: Central (e.g., motor recruitment) and peripheral (e.g., muscle atrophy) sources may alter muscle strength in individuals with stroke and further investigations are needed to partition and quantify their effects. As to the effect of strength training interventions in individuals with stroke, the majority of studies (albeit with small samples) that evaluated muscle strength as an outcome demonstrated improvements. With regard to the effect of strength training on functional outcomes in individuals with stroke, positive outcomes were found in less rigorous pre-test/post-test studies, but more conflicting results with controlled trials. CONCLUSIONS: Although there is some suggestion that strength training alone can improve muscle strength, further research is required to optimize strength training and the transfer of these strength gains to functional tasks in individuals with stroke.

How to interpret normal electromyographic findings in patients with an alleged history of polio

OBJECTIVE

In some patients with a history of polio, the electromyography is normal, not showing the typical neurogenic signs. The aim of this study was to explain the normal findings in electromyography, especially in paralytic polio.

DESIGN

Retrospective study.

SUBJECTS/METHODS

Concentric needle electromyography, macro electromyography (including single fibre electromyography) and neurography were performed in various combinations in 688 patients with an alleged history of polio.

RESULTS

Thirty-five patients with paralytic polio had normal or minimally abnormal neurophysiology. In 6 patients the diagnosis of polio was rejected and was instead found to be other diagnoses. Three patients had a very atypical history. Of the 26 with possible paralytic polio, 17 showed a strong suspicion of previous paralytic polio without any neurophysiological signs of degeneration of the anterior horn cells.

CONCLUSION

If neurophysiological findings are normal in patients with a history of polio, the original diagnosis may be incorrect. However, the absence of electromyography changes does not entirely exclude a previous history of polio with transient functional loss without degeneration of anterior horn cells vulnerable for later functional impairment.

The physiological functional loss of single thenar motor units in the stroke patients: when does it occur? Does it progress?

OBJECTIVE

We examined the time at which loss of functioning motor units occurs on the hemiparetic side, the relationship between that loss and hemiparetic severity, and how long that loss continues.

METHODS

Sample surface motor unit action potentials (S-MUAPs) were evoked in F-waves. They entirely represent the activity of the relative numbers of different shape S-MUAPs for each abductor pollicis brevis muscle. S-MUAPs from selected population of F-waves were averaged after aligning onset latency. Motor unit number was obtained by dividing the maximum M-potential negative peak amplitude by the averaged S-MUAP one.

RESULTS

The motor unit number on the hemiparetic side was significantly lower than that on the unaffected side in stroke patients who had suffered hemiparesis for more than 9 days. This motor unit loss was greater in patients with severe hemiparesis. One year after onset, the chronic stroke patients showed the same motor unit loss on hemiparetic side as they had 3-4 months after onset.

CONCLUSIONS

Motor unit loss on the hemiparetic side is present as early as the second week after onset and is correlated with hemiparesis severity, and this loss continues out to 1 year. This may be due to trans-synaptic degeneration that occurs secondarily to upper motor neuron lesion.

Submaximal exercise in persons with stroke: test-retest reliability and concurrent validity with maximal oxygen consumption11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated

OBJECTIVE

To establish the test-retest reliability and concurrent validity with maximum oxygen consumption (VO2max) for 3 submaximal exercise tests in persons with chronic stroke: (1) submaximal treadmill test, (2) submaximal cycle ergometer test, and (3) 6-minute walk test (6MWT).

DESIGN

Prospective study using a convenience sample.

SETTING

Free-standing tertiary rehabilitation center.

PARTICIPANTS

A volunteer sample of 12 community-dwelling individuals who had a stroke with moderate motor deficits.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Heart rate, blood pressure, and oxygen consumption (VO2) were assessed during the exercise tests.

RESULTS

Test-retest reliability was good to excellent for the exercise tests (maximal and submaximal tests). VO2 for all submaximal measures related to VO2max (r range, .66-.80). Neither the 6MWT distance, self-selected gait speed, nor hemodynamic measures related to VO2max.

CONCLUSION

The VO2 measures of the submaximal exercise tests had excellent reliability and good concurrent validity with VO2max. Submaximal exercise tests may be a method by which to monitor the effects of interventions after a screening test (eg, symptom-limited graded exercise test, dobutamine stress echocardiograph).