Tonic stretch reflex threshold as a measure of disordered motor control and spasticity - A critical review

The Tonic Stretch Reflex Threshold (TSRT) is the joint angle or muscle length (λ) at which muscle activation begins. In spasticity, the TSRT abnormally lies inside the biomechanical joint range. It is determined by measuring the Dynamic Stretch Reflex Thresholds (DSRTs) by stretching the resting muscle at different velocities. The metric μ, characterizes the velocity-sensitivity of the DSRTs and is expressed as the time required to lengthen the passive muscles from DSRT to TSRT at the respective stretch velocity. The original formulation of the TSRT, DSRT and μ is summarized. Then, a thorough search of literature prior to December 2023 was conducted that returned 25 papers that have used the technique. Eleven of these papers come from the research group of the authors, including 1 reporting on treatment effects. Of the remaining 14 papers, 11 report variations of the methodology with different populations and 3 report on the effects of an intervention. The review discusses how specific modifications to data collection and analysis procedures have either improved the methodology or, in some cases, led to uninterpretable results. The influence of modifications to the data collection and analysis procedures is discussed.

Effects of dry needling on spasticity and motor function in paralympic athletes: a study protocol for a randomised controlled trial

No study has evaluated the effects of dry needling on Paralympic athletes. Therefore, in this study, we will evaluate the effect of dry needling on lower limb spasticity and motor performance, as well as the range of motion of Paralympic athletes. The study will be a triple-blinded, randomised controlled trial. Twenty-four athletes aged 18-45 in T35-T38 groups of the International Paralympic Committee classification will be included in the study. Twelve participants will receive dry needling of the quadriceps and gastrocnemius muscles, and 12 will receive placebo treatment with sham needles at similar points. We will assess the spasticity of the quadriceps and gastrocnemius muscles using the Modified Ashworth Scale, evaluate motor function using the Selective Control Assessment of the Lower Extremity Scale and measure ankle range of motion (ROM) with a goniometer. Considering our hypothesis, the athletes who will undergo the dry needling are supposed to achieve better improvements in spasticity, ROM and motor performance. This study can provide useful information to help better decide on managing complications in Paralympics and its long-term outcomes, to cover the current lack in the literature.

Postural control deficits due to bilateral pyramidal tract lesions exemplified by hereditary spastic paraplegia (HSP) originate from increased feedback time delay and reduced long-term error corrections

Pyramidal tract lesions determine the clinical syndrome of Hereditary Spastic Paraplegia (HSP). The clinical impairments of HSP are typically exemplified by their deficits in mobility, leading to falls and injuries. The first aim of this study was to identify the cause for postural abnormalities caused by pyramidal tract lesions in HSP. The second aim was to specify the effect of treadmill training for postural abnormalities. We examined nine HSP patients before and after treadmill training, as well as nine healthy control subjects during perturbed and unperturbed stance. We found that HSP was associated with larger sway amplitudes and velocities. Body excursions following platform tilts were larger, and upper body excursions showed a phase lead. Model-based analysis detected a greater time delay and a reduced long-term error correction of postural reactions in the center of mass. HSP patients performed significantly better in clinical assessments after treadmill training. In addition, treadmill training reduced sway amplitudes and body excursions, most likely by increasing positional and velocity error correction gain as a compensatory mechanism, while the time delay and long-term error correction gain remained largely unaffected. Moreover, the upper body's phase lead was reduced. We conclude that HSP leads to very specific postural impairments. While postural control generally benefits from treadmill training, the effect seems to mainly rely on compensatory mechanisms, whereas the original deficits are not affected significantly.

Muscle Architecture Adaptations to Static Stretching Training: A Systematic Review with Meta-Analysis

BACKGROUND

Long-term stretching of human skeletal muscles increases joint range of motion through altered stretch perception and decreased resistance to stretch. There is also some evidence that stretching induces changes in muscle morphology. However, research is limited and inconclusive.

OBJECTIVE

To examine the effect of static stretching training on muscle architecture (i.e., fascicle length and fascicle angle, muscle thickness and cross-sectional area) in healthy participants.

DESIGN

Systematic review and meta-analysis.

METHODS

PubMed Central, Web of Science, Scopus, and SPORTDiscus were searched. Randomized controlled trials and controlled trials without randomization were included. No restrictions on language or date of publication were applied. Risk of bias was assessed using Cochrane RoB2 and ROBINS-I tools. Subgroup analyses and random-effects meta-regressions were also performed using total stretching volume and intensity as covariates. Quality of evidence was determined by GRADE analysis.

RESULTS

From the 2946 records retrieved, 19 studies were included in the systematic review and meta-analysis (n = 467 participants). Risk of bias was low in 83.9% of all criteria. Confidence in cumulative evidence was high. Stretching training induces trivial increases in fascicle length at rest (SMD = 0.17; 95% CI 0.01-0.33; p = 0.042) and small increases in fascicle length during stretching (SMD = 0.39; 95% CI 0.05 to 0.74; p = 0.026). No increases were observed in fascicle angle or muscle thickness (p = 0.30 and p = 0.18, respectively). Subgroup analyses showed that fascicle length increased when high stretching volumes were used (p < 0.004), while no changes were found for low stretching volumes (p = 0.60; subgroup difference: p = 0.025). High stretching intensities induced fascicle length increases (p < 0.006), while low stretching intensities did not have an effect (p = 0.72; subgroup difference: p = 0.042). Also, high intensity stretching resulted in increased muscle thickness (p = 0.021). Meta-regression analyses showed that longitudinal fascicle growth was positively associated with stretching volume (p < 0.02) and intensity (p < 0.04).

CONCLUSIONS

Static stretching training increases fascicle length at rest and during stretching in healthy participants. High, but not low, stretching volumes and intensities induce longitudinal fascicle growth, while high stretching intensities result in increased muscle thickness.

REGISTRATION

PROSPERO, registration number: CRD42021289884.

Predicting post-stroke motor recovery of upper extremity using clinical variables and performance assays: A prospective cohort study protocol

BACKGROUND AND PURPOSE

Measurement of movement quality is essential to distinguish motor recovery patterns and optimize rehabilitation strategies post-stroke. Recently, the Stroke Recovery and Rehabilitation Roundtable Taskforce (SRRR) recommended four kinetic and kinematic performance assays to measure upper extremity (UE) movements and distinguish behavioral restitution and compensation mechanisms early post-stroke. The purpose of this study is to develop and validate a prediction model to analyze the added prognostic value of performance assays over clinical variables assessed up to 1-month post stroke for predicting recovery of UE motor impairment, capacity and quality of movement (QoM) measured at 3 months post-stroke onset.

METHODS

In this prospective cohort study, 120 stroke survivors will be recruited within seven days post-stroke. Candidate predictors such as baseline characteristics, demographics and performance assays as per SRRR recommendations along with tonic stretch reflex threshold will be measured up to 1-month post-stroke. Upper extremity motor recovery will be evaluated in terms of motor impairment (Fugl-Meyer assessment for UE), UE capacity measured with Action Research Arm Test (ARAT) and QoM (movement smoothness in the form of peak metrics [PM]) assessed with a reach-to-grasp-to-mouth task (mimicking a drinking task) at 3 months post-stroke. Three multivariable linear regression models will be developed to predict factors responsible for the outcomes of Fugl-Meyer assessment for upper extremity (FM-UE), ARAT and movement quality. The developed models will be internally validated using a split-sample method.

DISCUSSION

This study will provide a validated prediction model inclusive of clinical and performance assays that may assist in prediction of UE motor recovery. Predicting the amount of recovery and differentiating between behavioral restitution and compensation (as reflected by the FM-UE, QoM and ARAT) would enable us in realistic goal formation and planning rehabilitation. It would also help in encouraging patients to partake in early post-stroke rehabilitation thus improving the recovery potential.

Effect of post-stroke spasticity on voluntary movement of the upper limb

Background

Hemiparesis following stroke is often accompanied by spasticity. Spasticity is one factor among the multiple components of the upper motor neuron syndrome that contributes to movement impairment. However, the specific contribution of spasticity is difficult to isolate and quantify. We propose a new method of quantification and evaluation of the impact of spasticity on the quality of movement following stroke.

Methods

Spasticity was assessed using the Tonic Stretch Reflex Threshold (TSRT). TSRT was analyzed in relation to stochastic models of motion to quantify the deviation of the hemiparetic upper limb motion from the normal motion patterns during a reaching task. Specifically, we assessed the impact of spasticity in the elbow flexors on reaching motion patterns using two distinct measures of the ‘distance’ between pathological and normal movement, (a) the bidirectional Kullback–Liebler divergence (BKLD) and (b) Hellinger’s distance (HD). These measures differ in their sensitivity to different confounding variables. Motor impairment was assessed clinically by the Fugl-Meyer assessment scale for the upper extremity (FMA-UE). Forty-two first-event stroke patients in the subacute phase and 13 healthy controls of similar age participated in the study. Elbow motion was analyzed in the context of repeated reach-to-grasp movements towards four differently located targets. Log-BKLD and HD along with movement time, final elbow extension angle, mean elbow velocity, peak elbow velocity, and the number of velocity peaks of the elbow motion were computed.

Results

Upper limb kinematics in patients with lower FMA-UE scores (greater impairment) showed greater deviation from normality when the distance between impaired and normal elbow motion was analyzed either with the BKLD or HD measures. The severity of spasticity, reflected by the TSRT, was related to the distance between impaired and normal elbow motion analyzed with either distance measure. Mean elbow velocity differed between targets, however HD was not sensitive to target location. This may point at effects of spasticity on motion quality that go beyond effects on velocity.

Conclusions

The two methods for analyzing pathological movement post-stroke provide new options for studying the relationship between spasticity and movement quality under different spatiotemporal constraints.

The mechanisms of adaptation for muscle fascicle length changes with exercise: Implications for spastic muscle

We are proposing optimal training conditions that can lead to an increase in the number of serial sarcomeres (SSN) and muscle fascicle length (FL) in spastic muscles. Therapeutic interventions for increasing FL in clinical populations with neurological origin, in whom relative shortness of muscle fascicles contributed to the presentation of symptoms such as spasticity, contracture, and limited functional abilities, do not generally meet these conditions, and therefore, result in less than satisfactory outcomes. Based on a review of literature, we argue that protocols of exercise interventions that led to sarcomerogenesis, and increases in SSN and FL in healthy animal and human models satisfied three criteria: 1) all involved eccentric exercise at appropriately high velocity; 2) resulted in positive strain of muscle fascicles; and 3) momentary deactivation in the stretched muscle. Accordingly, to increase FL in spastic muscles, new exercise protocols in which the three presumed criteria are satisfied, must be developed, and long-term muscle architectural and functional adaptations to such trainings must be examined.

Comparison of the temporal properties of medium latency responses induced by cortical and peripheral stimulation

Sudden foot dorsiflexion lengthens soleus muscle and activates stretch-based spinal reflexes. Dorsiflexion can be triggered by activating tibialis anterior (TA) muscle through peroneal nerve stimulation or transcranial magnetic stimulation (TMS) which evokes a response in the soleus muscle referred to as Medium Latency Reflex (MLR) or motor-evoked potential-80 (Soleus MEP80), respectively. This study aimed to examine the relationship between these responses in humans. Therefore, latency characteristics and correlation of responses between soleus MEP80 and MLR were investigated. We have also calculated the latencies from the onset of tibialis activity, i.e., subtracting of TA-MEP from MEP80 and TA direct motor response from MLR. We referred to these calculations as Stretch Loop Latency Central (SLLc) for MEP80 and Stretch Loop Latency Peripheral (SLLp) for MLR. The latency of SLLc was found to be 61.4 ± 5.6 ms which was significantly shorter (P = 0.0259) than SLLp (64.0 ± 4.2 ms) and these latencies were correlated (P = 0.0045, r = 0.689). The latency of both responses was also found to be inversely related to the response amplitude (P = 0.0121, r = 0.451) probably due to the activation of large motor units. When amplitude differences were corrected, i.e. investigating the responses with similar amplitudes, SLLp, and SLLc latencies found to be similar (P = 0.1317). Due to the identical features of the soleus MEP80 and MLR, we propose that they may both have spinal origins.

A novel mechatronic system for evaluating elbow muscular spasticity relying on Tonic Stretch Reflex Threshold estimation

Muscular spasticity represents one of the most common motor disorder associated to lesions of the Central Nervous System, such as Stroke, and affects joint mobility up to the complete prevention of skeletal muscle voluntary control. Its clinical evaluation is hence of fundamental relevance for an effective rehabilitation of the affected subjects. Standard assessment protocols are usually manually performed by humans, and hence their reliability strongly depends on the capabilities of the clinical operator performing the procedures. To overcome this limitation, one solution is the usage of mechatronic devices based on the estimation of the Tonic Stretch Reflex Threshold, which allows for a quite reliable and operator-independent evaluation. In this work, we present the design and characterization of a novel mechatronic device that targets the estimation of the Tonic Stretch Reflex Threshold at the elbow level, and, at the same time, it can potentially act as a rehabilitative system. Our device can deliver controllable torque/velocity stimulation and record functional parameters of the musculo-skeletal system (joint position, torque, and multi-channel ElectroMyoGraphyc patterns), with the ultimate goals of: i) providing significant information for the diagnosis and the classification of muscular spasticity, ii) enhancing the recovery evaluation of patients undergoing through therapeutic rehabilitation procedures and iii) enabling a future active usage of this device also as therapeutic tool.Clinical relevance- The contribution presented in this work proposes a technological advancement for a device-based evaluation of motion impairment related to spasticity, with a major potential impact on both the clinical appraisal and the rehabilitation procedures.

A Novel Quantitative Spasticity Evaluation Method Based on Surface Electromyogram Signals and Adaptive Neuro Fuzzy Inference System

Stroke patients often suffer from spasticity. Before treatment of spasticity, there are often practical demands for objective and quantitative assessment of muscle spasticity. However, the common quantitative spasticity assessment method, the tonic stretch reflex threshold (TSRT), is time-consuming and complicated to implement due to the requirement of multiple passive stretches. To evaluate spasticity conveniently, a novel spasticity evaluation method based on surface electromyogram (sEMG) signals and adaptive neuro fuzzy inference system (i.e., the sEMG-ANFIS method) was presented in this paper. Eleven stroke patients with spasticity and four healthy subjects were recruited to participate in the experiment. During the experiment, the Modified Ashworth scale (MAS) scores of each subject was obtained and sEMG signals from four elbow flexors or extensors were collected from several times (4–5) repetitions of passive stretching. Four time-domain features (root mean square, the zero-cross rate, the wavelength and a 4th-order autoregressive model coefficient) and one frequency-domain feature (the mean power frequency) were extracted from the collected sEMG signals to reflect the spasticity information. Using the ANFIS classifier, excellent regression performance was achieved [mean accuracy = 0.96, mean root-mean-square error (RMSE) = 0.13], outperforming the classical TSRT method (accuracy = 0.88, RMSE = 0.28). The results showed that the sEMG-ANFIS method not only has higher accuracy but also is convenient to implement by requiring fewer repetitions (4–5) of passive stretches. The sEMG-ANFIS method can help stroke patients develop proper rehabilitation training programs and can potentially be used to provide therapeutic feedback for some new spasticity interventions, such as shockwave therapy and repetitive transcranial magnetic stimulation.

Knee Muscle Stretch Reflex Responses After an Intrathecal Baclofen Bolus in Neurological Patients With Moderate-to-Severe Hypertonia

OBJECTIVES

To examine the prevalence, onset threshold, and response magnitude of stretch reflex response (SRR) in the knee extensors and flexors before and after an intrathecal baclofen (ITB) bolus injection in patients with moderate-to-severe hypertonia.

MATERIALS AND METHODS

SRRs were elicited by reciprocal passive knee extension/flexion movements at preset angular velocities of 5, 60, 120, 180, 240, and 300°/s using an isokinetic dynamometer and recorded with surface electromyographic (EMG) electrodes placed over the knee extensors and flexors in 53 neurologic patients before and at 2.5 and 5 hours after an ITB injection via lumbar puncture. Outcome measures included the number of patients with presence/absence of SRRs, the number of SRRs per session, SRR onset threshold angle and velocity, and response magnitudes (peak EMG and area under the EMG curve) for each muscle. Pre-post comparisons were completed using the Fisher's exact and Wilcoxon signed rank tests.

RESULTS

For both knee extensors and flexors, the proportion of patients with present SRRs (p < 0.0001) and the number of SRRs per session (p ≤ 0.027) decreased from pre- to post-ITB. The threshold velocity significantly increased post-injection in both muscles (p ≤ 0.001) without significant changes in the threshold angle. The response magnitudes significantly decreased in the knee extensors (p ≤ 0.016) but not the knee flexors after the injection.

CONCLUSIONS

The prevalence and threshold velocity of SRR emerged as the most robust and practical parameters for assessing hyperreflexia during ITB bolus trial that can complement clinical assessment of muscle hypertonia.

Spasticity Measurement Based on the HHT Marginal Spectrum Entropy of sEMG Using a Portable System: A Preliminary Study

To facilitate stretch reflex onset (SRO) detection and improve accuracy and reliability of spasticity assessment in clinical settings, a new method to measure dynamic stretch reflex threshold (DSRT) based on Hilbert-Huang transform marginal spectrum entropy (HMSEN) of surface electromyography (sEMG) signals and a portable system to quantify modified Ashworth scale (MAS) for spasticity assessment were developed. The sEMG signals were divided into frames using a fixed-length sliding window, and the HMSEN of each frame was calculated. An adaptive threshold was set to measure the DSRT. The HMSEN based method can quantify muscle activity through time-frequency and nonlinear dynamics analysis, therefore providing deeper insight about the spastic muscle mechanisms during stretching and a reliable SRO detection method. Experimental results revealed that the HMSEN based method could reliably detect the SRO and measure the DSRT (recognition rate: 95.45%), and could achieve improved performance over the time-domain based method. There was a strong correlation ( to -0.900) between the MAS scores and the DSRT index, and the test-retest reliability was high. Additionally, limitations of the MAS were analyzed. This paper indicates that the presented framework can provide a promising tool to measure DSRT and a clinical quantitative approach for spasticity assessment.

Modified motor unit number index (MUNIX) algorithm for assessing excitability of alpha motor neuron in spasticity

Objective

The understanding of the spasticity mechanism is still a problem in the literature, as its definition can be made on the basis of more than one parameter. Therefore, we studied alpha motor neuron excitability, dynamic changes based on force production, and patellar tendon (T) reflex in spasticity and healthy control groups.

Methods

Alpha motor neuron excitability, force production, and patellar T reflex were evaluated through three different test protocols. Motor Unit Number Index (MUNIX) measurement was applied for understanding motor neuron pool properties in the first protocol. Voluntary force production and patellar T reflex parameters were evaluated by voluntary force production and triggering patellar T reflex. Twenty spasticity and 20 healthy volunteers participated in the study.

Results

In the spasticity group, both MUNIX numbers and Motor Unit Size Index (MUSIX) numbers were lower than those in the control group. The results for the Ideal Case Motor Unit Count (ICMUC) parameter show that there is no significant difference between spasticity and healthy individuals for low-level contractions, whereas there is a significant difference for high-level contractions (p < 0.05). In the spasticity group, an increase was observed in the ratio of maximal voluntary force to the T reflex triggered force production (Tf/Vf).

Conclusion

Spasticity and healthy subjects can be distinguished easily and clearly by evaluating the changes in both kinesiological and electrophysiological findings and the decreasing threshold in the alpha motor neuron pool.

Significance

This study shows that such combined methods, which allow the evaluation of the alpha motor neuron pool, as well as kinesiological and electrophysiological parameters, are tools that cannot be overlooked in understanding spasticity.

Association of spasticity and motor dysfunction in chronic stroke

BACKGROUND

The prevalence of increased muscle tone after stroke is frequently reported as 30% to 40%, and the condition is often concurrent with motor control deficits, manifesting as an inability to isolate paretic-limb joint movements.

OBJECTIVE

The objectives of this retrospective analysis were to 1) report the prevalence of increased muscle tone in a convenience sample of 128 chronic stroke survivors with moderate/severe motor deficits and 2) quantify the relation between tone and motor impairment in chronic stroke survivors.

METHODS

Analyses included descriptive statistics and multiple regression modeling, with the modified Ashworth Scale score (MAS; tone) as a predictor of isolated joint movement control (Fugl-Meyer score [FM]; motor impairment).

RESULTS

Increased muscle tone was present in 97% of subjects. Increased muscle tone was associated with impaired motor control (FM; upper extremity, P=0.008; lower extremity, P=0.03) after adjusting for age, time since stroke and sex. We found a significant difference between flexor and extensor strength for finger, elbow, hip and knee joints (P<0.002). Participants were classified in high and low MAS score groups. With high MAS score and for muscles of finger flexion and forearm pronation, we found a trend toward impaired strength of antagonist muscles (finger extensors and forearm supinators, respectively) as compared with low MAS score for these same muscle pairings.

CONCLUSIONS

The prevalence of increased tone was higher in this study than in previous reports. Increased muscle tone in chronic stroke survivors with persistent motor dysfunction could be associated with impaired motor control and differential muscle strength of antagonistic muscles.

Measurement of post-stroke spasticity based on tonic stretch reflex threshold: implications of stretch velocity for clinical practice

PURPOSE

The most commonly used method for the clinical evaluation of spasticity is the modified Ashworth scale (MAS), which is subjective. In this regard, the spasticity assessment through the tonic stretch reflex threshold, which is an objective method, has emerged as an alternative. It is based on the value of the dynamic stretch reflex threshold, which is measured at different stretch velocities. However, by this definition, it is not possible to define the speed at which passive stretches should be performed during evaluation.

OBJECTIVE

This study aimed to evaluate whether the speed-variation sequence used to acquire the dynamic stretch reflex threshold influences the tonic stretch reflex threshold (TSRT) and, consequently, the estimation of spasticity by this method.

METHODS

Three forms of stretching-variation speed were adopted, i.e., increasing, decreasing, and randomised. The study was performed using 10 post-stroke patients.

RESULTS AND CONCLUSIONS

The results showed that the stretch protocols were not all the same and that the method of increasing was most suitable for performing manual passive stretches to evaluate TSRT in these patients. Another analysis was the correlation between MAS and tonic stretch reflex threshold; a weak correlation was observed between the increasing and decreasing methods, and moderate correlation was observed between the random methods. Implications for Rehabilitation We demonstrated that the protocol of execution of passive stretches influences in the measurement of the tonic stretch reflex threshold (TSRT). We recommend the method of increasing velocity for performing manual passive stretches. We also build software with a reliable biological data acquisition system, which makes acquisition and processing of data in real time. In this way, the TSRT is a promising quantitative measure to assess post-stroke spasticity, calculated automatically. We also we provided the use of portable instruments to facilitate the assessment of spasticity in clinical practice.

Modification of Spastic Stretch Reflexes at the Elbow by Flexion Synergy Expression in Individuals With Chronic Hemiparetic Stroke

OBJECTIVE

To systematically characterize the effect of flexion synergy expression on the manifestation of elbow flexor stretch reflexes poststroke, and to relate these findings to elbow flexor stretch reflexes in individuals without neurologic injury.

DESIGN

Controlled cohort study.

SETTING

Academic medical center.

PARTICIPANTS

Participants (N=20) included individuals with chronic hemiparetic stroke (n=10) and a convenience sample of individuals without neurologic or musculoskeletal injury (n=10).

INTERVENTIONS

Participants with stroke were interfaced with a robotic device that precisely manipulated flexion synergy expression (by regulating shoulder abduction loading) while delivering controlled elbow extension perturbations over a wide range of velocities. This device was also used to elicit elbow flexor stretch reflexes during volitional elbow flexor activation, both in the cohort of individuals with stroke and in a control cohort. In both cases, the amplitude of volitional elbow flexor preactivation was matched to that generated involuntarily during flexion synergy expression.

MAIN OUTCOME MEASURES

The amplitude of short- and long-latency stretch reflexes in the biceps brachii, assessed by electromyography, and expressed as a function of background muscle activation and stretch velocity.

RESULTS

Increased shoulder abduction loading potentiated elbow flexor stretch reflexes via flexion synergy expression in the paretic arm. Compared with stretch reflexes in individuals without neurologic injury, paretic reflexes were larger at rest but were approximately equal to control muscles at matched levels of preactivation.

CONCLUSIONS

Because flexion synergy expression modifies stretch reflexes in involved muscles, interventions that reduce flexion synergy expression may confer the added benefit of reducing spasticity during functional use of the arm.

Spasticity Measurement Based on Tonic Stretch Reflex Threshold in Children with Cerebral Palsy Using the PediAnklebot

Nowadays, objective measures are becoming prominent in spasticity assessment, to overcome limitations of clinical scales. Among others, Tonic Stretch Reflex Threshold (TSRT) showed promising results. Previous studies demonstrated the validity and reliability of TSRT in spasticity assessment at elbow and ankle joints in adults. Purposes of the present study were to assess: (i) the feasibility of measuring TSRT to evaluate spasticity at the ankle joint in children with Cerebral Palsy (CP), and (ii) the correlation between objective measures and clinical scores. A mechatronic device, the pediAnklebot, was used to impose 50 passive stretches to the ankle of 10 children with CP and 3 healthy children, to elicit muscles response at 5 different velocities. Surface electromyography, angles, and angular velocities were recorded to compute dynamic stretch reflex threshold; TSRT was computed with a linear regression through angles and angular velocities. TSRTs for the most affected side of children with CP resulted into the biomechanical range (95.7 ± 12.9° and 86.7 ± 17.4° for Medial and Lateral Gastrocnemius, and 75.9 ± 12.5° for Tibialis Anterior). In three patients, the stretch reflex was not elicited in the less affected side. TSRTs were outside the biomechanical range in healthy children. However, no correlation was found between clinical scores and TSRT values. Here, we demonstrated the capability of TSRT to discriminate between spastic and non-spastic muscles, while no significant outcomes were found for the dorsiflexor muscle.

An ovine model of spinal cord injury

OBJECTIVE

To develop a large animal model of spinal cord injury (SCI), for use in translational studies of spinal cord stimulation (SCS) in the treatment of spasticity. We seek to establish thresholds for the SCS parameters associated with reduction of post-SCI spasticity in the pelvic limbs, with implications for patients.

STUDY DESIGN

The weight-drop method was used to create a moderate SCI in adult sheep, leading to mild spasticity in the pelvic limbs. Electrodes for electromyography (EMG) and an epidural spinal cord stimulator were then implanted. Behavioral and electrophysiological data were taken during treadmill ambulation in six animals, and in one animal with and without SCS at 0.1, 0.3, 0.5, and 0.9 V.

SETTING

All surgical procedures were carried out at the University of Iowa. The gait measurements were made at Iowa State University.

MATERIAL AND METHODS

Nine adult female sheep were used in these institutionally approved protocols. Six of them were trained in treadmill ambulation prior to SCI surgeries, and underwent gait analysis pre- and post-SCI. Stretch reflex and H-reflex measurements were also made in conscious animals.

RESULTS

Gait analysis revealed repeatable quantitative differences in 20% of the key kinematic parameters of the sheep, pre- and post-SCI. Hock joint angular velocity increased toward the normal pre-injury baseline in the animal with SCS at 0.9 V.

CONCLUSION

The ovine model is workable as a large animal surrogate suitable for translational studies of novel SCS therapies aimed at relieving spasticity in patients with SCI.

Spasticity, Motor Recovery, and Neural Plasticity after Stroke

Spasticity and weakness (spastic paresis) are the primary motor impairments after stroke and impose significant challenges for treatment and patient care. Spasticity emerges and disappears in the course of complete motor recovery. Spasticity and motor recovery are both related to neural plasticity after stroke. However, the relation between the two remains poorly understood among clinicians and researchers. Recovery of strength and motor function is mainly attributed to cortical plastic reorganization in the early recovery phase, while reticulospinal (RS) hyperexcitability as a result of maladaptive plasticity, is the most plausible mechanism for poststroke spasticity. It is important to differentiate and understand that motor recovery and spasticity have different underlying mechanisms. Facilitation and modulation of neural plasticity through rehabilitative strategies, such as early interventions with repetitive goal-oriented intensive therapy, appropriate non-invasive brain stimulation, and pharmacological agents, are the keys to promote motor recovery. Individualized rehabilitation protocols could be developed to utilize or avoid the maladaptive plasticity, such as RS hyperexcitability, in the course of motor recovery. Aggressive and appropriate spasticity management with botulinum toxin therapy is an example of how to create a transient plastic state of the neuromotor system that allows motor re-learning and recovery in chronic stages.

Current Practices of Physical and Occupational Therapists Regarding Spasticity Assessment and Treatment

Purpose: The purpose of this study was to understand current trends in rehabilitation practice regarding spasticity assessment and treatment. Method: The clinical practices of Canadian physiotherapists and occupational therapists in assessing and treating spasticity were investigated using a self-administered, Web-based questionnaire (cross-sectional design). Experienced clinicians developed the questionnaire, which surveyed socio-demographic characteristics, work environment, and clinician satisfaction with spasticity assessments and preferences for treatment. Results: A total of 317 clinicians (204 physiotherapists and 113 occupational therapists) completed the questionnaire. The majority of participants reported that using valid and reliable outcome measures to assess spasticity was important (91.1%). Most clinicians indicated using a combination of spasticity assessments, and their level of satisfaction with these assessments was very high. All clinicians believed that spasticity should be evaluated by rehabilitation professionals, and most indicated that it should be assessed by more than one professional. Although 83.8% indicated that spasticity should be tested on admission, a much lower percentage believed that it should be evaluated throughout rehabilitation. Most clinicians (92.2%) reported using multiple treatment modalities for spasticity. Conclusions: This study is the first to document clinicians' practices regarding spasticity assessment and treatment. A better understanding of current trends in physiotherapy and occupational therapy will help in tailoring strategies to improve practice.

Spatial control of reflexes, posture and movement in normal conditions and after neurological lesions

Control of reflexes is usually associated with central modulation of their sensitivity (gain) or phase-dependent inhibition and facilitation of their influences on motoneurons (reflex gating). Accumulated empirical findings show that the gain modulation and reflex gating are secondary, emergent properties of central control of spatial thresholds at which reflexes become functional. In this way, the system pre-determines, in a feedforward and task-specific way, where, in a spatial domain or a frame of reference, muscles are allowed to work without directly prescribing EMG activity and forces. This control strategy is illustrated by considering reflex adaptation to repeated muscle stretches in healthy subjects, a process associated with implicit learning and generalization. It has also been shown that spasticity, rigidity, weakness and other neurological motor deficits may have a common source - limitations in the range of spatial threshold control elicited by neural lesions.

Tonic Stretch Reflex Threshold as a Measure of Ankle Plantar-Flexor Spasticity After Stroke

BACKGROUND

Commonly used spasticity scales assess the resistance felt by the evaluator during passive stretching. These scales, however, have questionable validity and reliability. The tonic stretch reflex threshold (TSRT), or the angle at which motoneuronal recruitment begins in the resting state, is a promising alternative for spasticity measurement. Previous studies showed that spasticity and voluntary motor deficits after stroke may be characterized by a limitation in the ability of the central nervous system to regulate the range of the TSRT.

OBJECTIVE

The study objective was to assess interevaluator reliability for TSRT plantar-flexor spasticity measurement.

DESIGN

This was an interevaluator reliability study.

METHODS

In 28 people after stroke, plantar-flexor spasticity was evaluated twice on the same day. Plantar-flexor muscles were stretched 20 times at different velocities assigned by a portable device. Plantar-flexor electromyographic signals and ankle angles were used to determine dynamic velocity-dependent thresholds. The TSRT was computed by extrapolating a regression line through dynamic velocity-dependent thresholds to the angular axis.

RESULTS

Mean TSRTs in evaluations 1 and 2 were 66.0 degrees (SD=13.1°) and 65.8 degrees (SD=14.1°), respectively, with no significant difference between them. The intraclass correlation coefficient (2,1) was .851 (95% confidence interval=.703, .928).

LIMITATIONS

The notion of dynamic stretch reflex threshold does not exclude the possibility that spasticity is dependent on acceleration, as well as on velocity; future work will study both possibilities.

CONCLUSIONS

Tonic stretch reflex threshold interevaluator reliability for evaluating stroke-related plantar-flexor spasticity was very good. The TSRT is a reliable measure of spasticity. More information may be gained by combining the TSRT measurement with a measure of velocity-dependent resistance.

Fifty Years of Physics of Living Systems

The equilibrium-point hypothesis and its more recent version, the referent configuration hypothesis, represent the physical approach to the neural control of action. This hypothesis can be naturally combined with the idea of hierarchical control of movements and of synergic organization of the abundant systems involved in all actions. Any action starts with defining trajectories of a few referent coordinates for a handful of salient task-specific variables. Further, referent coordinates at hierarchically lower levels emerge down to thresholds of the tonic stretch reflex for the participating muscles. Stability of performance with respect to salient variables is reflected in the structure of inter-trial variance and phenomena of motor equivalence. Three lines of recent research within this framework are reviewed. First, synergic adjustments of the referent coordinate and apparent stiffness have been demonstrated during finger force production supporting the main idea of control with referent coordinates. Second, the notion of unintentional voluntary movements has been introduced reflecting unintentional drifts in referent coordinates. Two types of unintentional movements have been observed with different characteristic times. Third, this framework has been applied to studies of impaired movements in neurological patients. Overall, the physical approach searching for laws of nature underlying biological movement has been highly stimulating and productive.

Correlation of Resting Elbow Angle with Spasticity in Chronic Stroke Survivors

OBJECTIVE

To evaluate whether resting joint angle is indicative of severity of spasticity of the elbow flexors in chronic stroke survivors.

METHODS

Seventeen hemiparetic stroke subjects (male: n = 13; female: n = 4; age: 37-89 years; 11 right and 6 left hemiplegia; averaged 54.8 months after stroke, ranging 12-107 months) participated in the study. The number of subjects with modified Ashworth scale score (MAS) = 0, 1, 1+, 2, and 3 was 3, 3, 5, 3, and 3, respectively. In a single experimental session, resting elbow joint angle, MAS, and Tardieu scale score (Tardieu R1) were measured. A customized motorized stretching device was used to stretch elbow flexors at 5, 50, and 100°/s, respectively. Biomechanical responses (peak reflex torque and reflex stiffness) of elbow flexors were quantified. Correlation analyses between clinical and biomechanical assessments were performed.

RESULTS

Resting elbow joint angle showed a strong positive correlation with Tardieu R1 (r = 0.77, p < 0.01) and a very strong negative correlation with MAS (r = -0.89, p < 0.01). The resting angle also had strong correlations with biomechanical measures (r = -0.63 to -0.76, p < 0.01).

CONCLUSION

Our study provides experimental evidence for anecdotal observation that the resting elbow joint angle correlates with severity of spasticity in chronic stroke. Resting angle observation for spasticity assessment can and will be an easy, yet a valid way of spasticity estimation in clinical settings, particularly for small muscles or muscles which are not easily measurable by common clinical methods.

Perceptual and instrumental assessments of orofacial muscle tone in dysarthric and normal speakers

Clinical assessment of orofacial muscle tone is of interest for differential diagnosis of the dysarthrias, but standardized procedures and normative data are lacking. In this study, perceptual ratings of tone were compared with instrumental measures of tissue stiffness for facial, lingual, and masticatory muscles in 70 individuals with dysarthria. Perceptual and instrumental tone data were discordant and failed to discriminate between five dysarthria types. These results raised concerns about the validity of Myoton-3 stiffness measures in the orofacial muscles. Therefore, a second study evaluated contracted and relaxed orofacial muscles in 10 neurotypical adults. Results for the cheek, masseter, and lateral tongue surface followed predictions, with significantly higher tissue stiffness during contraction. In contradiction, stiffness measures from the superior surface of the tongue were lower during contraction. Superior-to-inferior tongue thickness was notably increased during contraction. A third study revealed that tissue thickness up to ~10 mm significantly affected Myoton-3 measures. Altered tissue thickness due to neuromuscular conditions like spasticity and atrophy may have undermined the detection of group differences in the original sample of dysarthric speakers. These experiments underscore the challenges of assessing orofacial muscle tone and identify considerations for quantification of tone-related differences across dysarthria groups in future studies.

Spasticity and its contribution to hypertonia in cerebral palsy

Spasticity is considered an important neural contributor to muscle hypertonia in children with cerebral palsy (CP). It is most often treated with antispasticity medication, such as Botulinum Toxin-A. However, treatment response is highly variable. Part of this variability may be due to the inability of clinical tests to differentiate between the neural (e.g., spasticity) and nonneural (e.g., soft tissue properties) contributions to hypertonia, leading to the terms “spasticity” and “hypertonia” often being used interchangeably. Recent advancements in instrumented spasticity assessments offer objective measurement methods for distinction and quantification of hypertonia components. These methods can be applied in clinical settings and their results used to fine-tune and improve treatment. We reviewed current advancements and new insights with respect to quantifying spasticity and its contribution to muscle hypertonia in children with CP. First, we revisit what is known about spasticity in children with CP, including the various definitions and its pathophysiology. Second, we summarize the state of the art on instrumented spasticity assessment in CP and review the parameters developed to quantify the neural and nonneural components of hypertonia. Lastly, the impact these quantitative parameters have on clinical decision-making is considered and recommendations for future clinical and research investigations are discussed.

Muscle activation patterns when passively stretching spastic lower limb muscles of children with cerebral palsy

The definition of spasticity as a velocity-dependent activation of the tonic stretch reflex during a stretch to a passive muscle is the most widely accepted. However, other mechanisms are also thought to contribute to pathological muscle activity and, in patients post-stroke and spinal cord injury can result in different activation patterns. In the lower-limbs of children with spastic cerebral palsy (CP) these distinct activation patterns have not yet been thoroughly explored. The aim of the study was to apply an instrumented assessment to quantify different muscle activation patterns in four lower-limb muscles of children with CP. Fifty-four children with CP were included (males/females n = 35/19; 10.8±3.8 yrs; bilateral/unilateral involvement n =  32/22; Gross Motor Functional Classification Score I–IV) of whom ten were retested to evaluate intra-rater reliability. With the subject relaxed, single-joint, sagittal-plane movements of the hip, knee, and ankle were performed to stretch the lower-limb muscles at three increasing velocities. Muscle activity and joint motion were synchronously recorded using inertial sensors and electromyography (EMG) from the adductors, medial hamstrings, rectus femoris, and gastrocnemius. Muscles were visually categorised into activation patterns using average, normalized root mean square EMG (RMS-EMG) compared across increasing position zones and velocities. Based on the visual categorisation, quantitative parameters were defined using stretch-reflex thresholds and normalized RMS-EMG. These parameters were compared between muscles with different activation patterns. All patterns were dominated by high velocity-dependent muscle activation, but in more than half, low velocity-dependent activation was also observed. Muscle activation patterns were found to be both muscle- and subject-specific (p<0.01). The intra-rater reliability of all quantitative parameters was moderate to good. Comparing RMS-EMG between incremental position zones during low velocity stretches was found to be the most sensitive in categorizing muscles into activation patterns (p<0.01). Future studies should investigate whether muscles with different patterns react differently to treatment.

Trunk Restraint to Promote Upper Extremity Recovery in Stroke Patients

Background. Many stroke patients exhibit excessive compensatory trunk movements during reaching. Compensatory movement behaviors may improve upper extremity function in the short-term but be detrimental to long-term recovery. Objective. To evaluate the evidence that trunk restraint limits compensatory trunk movement and/or promotes better upper extremity recovery in stroke patients. Methods. A search was conducted through electronic databases from January 1980 to June 2013. Only randomized controlled trials (RCTs) comparing upper extremity training with and without trunk restraint were selected for review. Three review authors independently assessed the methodological quality and extracted data from the studies. Meta-analysis was conducted when there was sufficient homogenous data. Results. Six RCTs involving 187 chronic stroke patients were identified. Meta-analysis of key outcome measures showed that trunk restraint has a moderate statistically significant effect on improving Fugl-Meyer Upper Extremity (FMA-UE) score, active shoulder flexion, and reduction in trunk displacement during reaching. There was a small, nonsignificant effect of trunk restraint on upper extremity function. Conclusion. Trunk restraint has a moderate effect on reduction of upper extremity impairment in chronic stroke patients, in terms of FMA-UE score, increased shoulder flexion, and reduction in excessive trunk movement during reaching. There is insufficient evidence to demonstrate that trunk restraint improves upper extremity function and reaching trajectory smoothness and straightness in chronic stroke patients. Future research on stroke patients at different phases of recovery and with different levels of upper extremity impairment is recommended.

Stretch reflex spatial threshold measure discriminates between spasticity and rigidity

OBJECTIVE

Muscle spasticity following stroke has been shown to result from limitations in the range of regulation of the tonic reflex spatial threshold (ST), i.e., the joint angle at which the stretch reflex begins to act due to descending and segmental influences on motoneurons. The purpose of this study was to determine whether spasticity due to stroke and rigidity due to parkinsonism can be discriminated based on the ST measure.

METHODS

Elbow muscles were stretched at different velocities in healthy, stroke (spasticity) and parkinsonism (rigidity) subjects. The elbow angle at which muscle activation began for each stretch velocity (dynamic ST) and the velocity sensitivity of the ST were measured. Dynamic ST values extrapolated to zero velocity defined the tonic ST.

RESULTS

Compared to healthy subjects, spasticity and rigidity were associated with a decrease in the range of central regulation of tonic STs. STs were hypersensitive in spastic muscles and either hypo- or inversely sensitive to stretch velocity in rigid muscles.

CONCLUSIONS

ST characteristics discriminate between neurological deficits of muscle tone.

SIGNIFICANCE

Results suggest that spasticity and rigidity result from deficits in descending facilitatory control combined with deficits in dynamic fusimotor or/and presynaptic control of Ia inputs to motoneurons.

The Correlation between Modified Ashworth Scale and Biceps T-reflex and Inter-rater and Intra-rater Reliability of Biceps T-reflex

Objective

To establish a correlation between the modified Ashworth scale (MAS) and amplitude and latency of T-reflex and to demonstrate inter-rater and intra-rater reliability of the T-reflex of the biceps muscle for assessing spasticity after stroke.

Method

A total of 21 patients with hemiplegia and spasticity after ischemic stroke were enrolled for this study. The spasticity of biceps muscle was evaluated by an occupational therapist using the MAS. The mean value of manual muscle test of biceps muscles was 2.3±0.79. Latency and amplitude of T-reflex were recorded from biceps muscles by two physicians. The onset latency and peak to peak amplitude of the mean of 5 big T-reflex were measured. The examinations were carried out by two physicians at the same time to evaluate the inter-rater reliability. Further, one of the physicians performed the examination again after one week to evaluate the intra-rater reliability. The correlations between MAS and T-reflex, and the intra- and inter-rater reliability of biceps T-reflex were established by calculating the Spearman correlation coefficients and the intra-class correlation coefficients (ICCs).

Results

Amplitude of the biceps T-reflex increased with increasing level of MAS (r_s=0.464 and 0.573, respectively, p<0.01). ICCs of latency and amplitude of biceps T-reflex were 0.914 and 0.822. The Spearman correlation coefficients of latency and amplitude of biceps T-reflex were 0.937 and 0.635, respectively (p<0.01).

Conclusion

Biceps T-reflex demonstrates a good quantitative measurement and correlation tool with MAS for spasticity, and also shows acceptable inter- and intra-rater reliability, which can be used for patients with spasticity after stroke.

The gap between clinical gaze and systematic assessment of movement disorders after stroke

Background

Movement disorders after stroke are still captured by clinical gaze and translated to ordinal scores of low resolution. There is a clear need for objective quantification, with outcome measures related to pathophysiological background. Neural and non-neural contributors to joint behavior should be separated using different measurement conditions (tasks) and standardized input signals (force, position and velocity).

Methods

We reviewed recent literature for the application of biomechanical and/or elektromyographical (EMG) outcome measures under various measurement conditions in clinical research.

Results

Since 2005, 36 articles described the use of biomechanical and/or EMG outcome measures to quantify post-stroke movement disorder. Nineteen of the articles strived to separate neural and non-neural components. Only 6 of the articles measured biomechanical and EMG outcome measures simultaneously, while applying active and passive tasks and multiple velocities.

Conclusion

The distinction between neural and non-neural components to separately assess paresis, stiffness and muscle overactivity is not commonplace yet, while a large gap is to be bridged to attain reproducible and comparable results. Pathophysiologically clear concepts, substantiated with a comprehensive and concise measuring protocol will help professionals to identify and treat limiting factors in movement capabilities of post-stroke patients.

Effect of ankle-foot orthosis on postural control after stroke: a systematic review

INTRODUCTION

Stroke is currently the main cause of permanent disability in adults. The impairments are a combination of sensory, motor, cognitive and emotional changes that result in restrictions on the ability to perform basic activities of daily living (BADL). Postural control is affected and causes problems with static and dynamic balance, thus increasing the risk of falls and secondary injuries. The purpose of this review was to compile the literature to date, and assess the impact of ankle-foot orthosis (AFO) on postural control and gait in individuals who have suffered a stroke.

DEVELOPMENT

The review included randomised and controlled trials that examined the effects of AFO in stroke patients between 18 and 80 years old, with acute or chronic evolution. No search limits on the date of the studies were included, and the search lasted until April 2011. The following databases were used: Pubmed, Trip Database, Cochrane library, Embase, ISI Web Knowledge, CINHAL and PEDro. Intervention succeeded in improving some gait parameters, such as speed and cadence. However it is not clear if there was improvement in the symmetry, postural sway or balance.

CONCLUSIONS

Because of the limitations of this systematic review, due to the clinical diversity of the studies and the methodological limitations, 0these results should be considered with caution.

Evaluation of spasticity in children with cerebral palsy using Ashworth and Tardieu Scales compared with laboratory measures

The content validity of the Tardieu Scale and the Ashworth Scale was assessed in 27 independently ambulant children with cerebral palsy (gender: 17 males, 10 females; age: 5-9 years; Gross Motor Function Classification: level I and II). Ashworth and Tardieu Scale scores and laboratory measures of spasticity and contracture were collected from the plantarflexor muscles by 2 examiners who were blinded to the results. The Tardieu Scale was more effective than the Ashworth Scale in identifying the presence of spasticity (88.9%, kappa = 0.73; P = .000), the presence of contracture (77.8%, kappa = 0.503; P = .008) and the severity of contracture (r = 0.49; P = .009). However, neither scale was able to identify the severity of spasticity. The Tardieu Scale can provide useful information in children with cerebral palsy because it differentiates spasticity from contracture. However, a more comprehensive clinical method of testing neural and non-neural contributions to impairments and function is needed.