Shuo Hsiu Chang

Spasticity, weakness, force variability, and sustained spontaneous motor unit discharges of resting spastic–paretic biceps brachii muscles in chronic stroke

Introduction: The purpose of our study was to examine relations among spasticity, weakness, force variability, and sustained spontaneous motor unit discharges in spastic–paretic biceps brachii muscles in chronic stroke. Methods: Ten chronic stroke subjects produced submaximal isometric elbow flexion force on impaired and non‐impaired sides. Intramuscular EMG (iEMG) was recorded from biceps and triceps brachii muscles. Results: We observed sustained spontaneous motor unit discharges in resting biceps on iEMG. Spontaneous discharges increased after voluntary activation only on the impaired side. The impaired side had greater matching errors and greater fluctuations in isometric force. Spontaneous discharges were not related functionally to spasticity, force variability, or weakness. However, greater strength on the impaired side correlated with less force variability. Conclusion: Weakness rather than spasticity is a main factor interfering with voluntary force control in paretic–spastic biceps brachii muscles in chronic stroke. Muscle Nerve, 2013

Measurement of Paretic–Lower-Extremity Loading and Weight Transfer After Stroke

Background: Weight bearing through, or “loading” of, the paretic lower extremity and transfer of weight from one lower extremity to the other are important impairment-level goals of stroke rehabilitation. Improvements in these limb-loading and weight-transfer abilities have been shown to relate to improved performance of many functional activities. Unfortunately, valid and practical clinical measures of paretic–lower-extremity loading and weight transfer have not been identified. Objective: The purpose of this study was to assess convergent validity of the Step Test (ST) and the knee extension component of the Upright Motor Control Test (UMCe) as measures of paretic-limb loading and of the Repetitive Reach Test (RR) as a measure of weight transfer in the first 6 months after stroke. Design: This was a prospective cohort study of 33 adults with lower-extremity motor impairment following unilateral, noncerebellar stroke. Participants were tested one time per month from 1 to 6 months poststroke. Results: Scores on the ST (performed with the nonparetic leg as the stepping leg) and UMCe were positively correlated with peak vertical ground reaction forces (GRFs) beneath the paretic limb during functional tasks (R2=.35–.76 for the ST, pseudo R2=.21–.34 for the UMCe). Scores on the RR were positively correlated with change in vertical GRF beneath the paretic limb during the diagonal reach task (R2=.45) and with weight-transfer time during stepping with the nonparetic limb (R2=.15). Conclusions: The ST, performed with the nonparetic leg as the stepping leg, is a valid measure of paretic-limb loading during stroke recovery. Of the clinical measures tested, the ST correlated most strongly with the force platform measures.

Heat Stress and Cardiovascular, Hormonal, and Heat Shock Proteins in Humans

CONTEXT Conditions such as osteoarthritis, obesity, and spinal cord injury limit the ability of patients to exercise, preventing them from experiencing many well-documented physiologic stressors. Recent evidence indicates that some of these stressors might derive from exercise-induced body temperature increases. OBJECTIVE To determine whether whole-body heat stress without exercise triggers cardiovascular, hormonal, and extracellular protein responses of exercise. DESIGN Randomized controlled trial. SETTING University research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty-five young, healthy adults (13 men, 12 women; age = 22.1 ± 2.4 years, height = 175.2 ± 11.6 cm, mass = 69.4 ± 14.8 kg, body mass index = 22.6 ± 4.0) volunteered. INTERVENTION(S) Participants sat in a heat stress chamber with heat (73°C) and without heat (26°C) stress for 30 minutes on separate days. We obtained blood samples from a subset of 13 participants (7 men, 6 women) before and after exposure to heat stress. MAIN OUTCOME MEASURE(S) Extracellular heat shock protein (HSP72) and catecholamine plasma concentration, heart rate, blood pressure, and heat perception. RESULTS After 30 minutes of heat stress, body temperature measured via rectal sensor increased by 0.8°C. Heart rate increased linearly to 131.4 ± 22.4 beats per minute (F₆,₂₄ = 186, P < .001) and systolic and diastolic blood pressure decreased by 16 mm Hg (F₆,₂₄ = 10.1, P < .001) and 5 mm Hg (F₆,₂₄ = 5.4, P < .001), respectively. Norepinephrine (F₁,₁₂ = 12.1, P = .004) and prolactin (F₁,₁₂ = 30.2, P < .001) increased in the plasma (58% and 285%, respectively) (P < .05). The HSP72 (F₁,₁₂ = 44.7, P < .001) level increased with heat stress by 48.7% ± 53.9%. No cardiovascular or blood variables showed changes during the control trials (quiet sitting in the heat chamber with no heat stress), resulting in differences between heat and control trials. CONCLUSIONS We found that whole-body heat stress triggers some of the physiologic responses observed with exercise. Future studies are necessary to investigate whether carefully prescribed heat stress constitutes a method to augment or supplement exercise.

Step Test Scores Are Related to Measures of Activity and Participation in the First 6 Months After Stroke

Background: The Step Test (ST) is a measure of dynamic standing balance and paretic–lower-extremity motor control in patients with stroke. Little is known about the extent to which impairments assessed by the ST relate to activity and participation during stroke recovery. Objective: The purpose of this study was to determine relationships between ST scores and measures of activity and participation during the first 6 months after stroke. Design: This was a prospective cohort study. Methods: Thirty-three individuals (18 men, 15 women) with a diagnosis of a single, unilateral stroke participated in the study. Participants were tested one time per month from 1 to 6 months poststroke. The ST was considered an impairment-level measure. Self-selected gait speed and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) Physical Function Index (PFI) were used to assess physical function. Three domains (mobility, basic and instrumental activities of daily living, participation) of the Stroke Impact Scale were used to assess self-reported disability. Regression analyses were conducted to examine the bivariate associations between ST scores and each physical function and disability measure at each time point (1–6 months). Results: The ST scores were positively associated with both physical function measures. The associations were stronger for self-selected gait speeds (R2=.60–.79) than for the PFI scores (R2=.32–.60). During the first 6 months after stroke, each additional step with the paretic lower extremity on the ST corresponded to a 0.07-m/s to 0.09-m/s increase in gait speed, and each additional step with the nonparetic lower extremity was associated with a 0.07-m/s to 0.08-m/s gait speed increase. The impairment-disability associations were weaker than the impairment-physical function associations. Limitations: Limitations of the study include a relatively small sample size and lack of examiner blinding with regard to participant characteristics. Conclusions: Impairments in balance and paretic–lower-extremity motor control, as measured by the ST, relate to physical function and disability during the first 6 months following stroke.

Effects of an exercise program to increase hip abductor muscle strength and improve lateral stability following stroke: a single subject design.

Background and Purpose: Persons with lower extremity weakness following stroke often demonstrate difficulty with weight transfer and paretic lower extremity loading. These deficits, in turn, can lead to problems with lateral stability, or the ability to control movement of the center of mass in the frontal plane. The primary aim of this study was to examine the efficacy of an individualized home exercise program in improving hip abductor muscle strength and lateral stability in a subject with chronic stroke. Methods: An A‐B‐A treatment‐withdrawal single‐subject design was used. The subject was a 70‐year‐old male who had experienced a left hemispheric stroke 36 months prior to initiation of the study. Bilateral hip abductor muscle strength, single limb stance (SLS), timed 360° turn, Step Test, and 10‐m walk at self‐selected and fast speeds were recorded at regular intervals during the baseline (A‐1), treatment (B), and treatment‐withdrawal (A‐2) phases. The home exercise program in the B phase consisted of lower extremity weight bearing and weight transfer activities and exercise on a lateral training device 3 to 5 times a week for 6 weeks. The Berg Balance Scale (BBS) and Stroke Impact Scale (SIS) were administered at the completion of each phase and at 6‐week follow‐up. Data were analyzed using visual analysis and the split‐middle method of trend estimation. Results: Mean levels of all measures improved from A‐1 to B phases, with signi⊠cant increases in trend for hip abductor muscle strength and SLS bilaterally. Most improvements were maintained during the treatment‐withdrawal (A‐2) phase and at follow‐up. Conclusion: A home exercise program that includes exercise on a lateral training device shows promise for producing increases in hip abductor muscle strength and accompanying improvements in some measures of physical performance and disability in persons with chronic stroke.

Enhancing Muscle Force and Femur Compressive Loads Via Feedback-Controlled Stimulation of Paralyzed Quadriceps in Humans

OBJECTIVE To compare paralyzed quadriceps force properties and femur compressive loads in an upright functional task during conventional constant-frequency stimulation and force feedback-modulated stimulation. DESIGN Crossover trial. SETTING Research laboratory. PARTICIPANTS Subjects (N=13; 12 men, 1 woman) with motor-complete spinal cord injury. INTERVENTIONS Subjects performed 2 bouts of 60 isometric quadriceps contractions while supported in a standing frame. On separate days, subjects received constant-frequency stimulation at 20Hz (CONST) or frequency-modulated stimulation triggered by a change in force (FDBCK). During FDBCK, a computer algorithm responded to each 10% reduction in force with a 20% increase in stimulation frequency. MAIN OUTCOME MEASURES A biomechanical model was used to derive compressive loads on the femur, with a target starting dose of load equal to 1.5 times body weight. RESULTS Peak quadriceps force and fatigue index were higher for FDBCK than CONST (P<.05). Within-train force decline was greater during FDBCK bouts, but mean force remained above CONST values (P<.05). As fatigue developed during repetitive stimulation, FDBCK was superior to CONST for maintenance of femur compressive loads (P<.05). CONCLUSIONS Feedback-modulated stimulation in electrically activated stance is a viable method to maximize the physiologic performance of paralyzed quadriceps muscle. Compared with CONST, FDBCK yielded compressive loads that were closer to a targeted dose of stress with known osteogenic potential. Optimization of muscle force with FDBCK may be a useful tactic for future training-based antiosteoporosis protocols.

Interlimb interactions during bilateral voluntary elbow flexion tasks in chronic hemiparetic stroke

The purpose was to systematically investigate interlimb interactions in chronic hemiparetic stroke. Fourteen poststroke hemiparetic subjects (>1 year) performed maximum voluntary contraction (MVC) elbow flexion tasks without visual feedback with one (unilateral) and two limbs simultaneously (bilateral). At submaximal levels, subjects produced force to a visual target reflecting 20%, 40%, 60%, and 80% of corresponding MVC in unilateral tasks, and of summated unilateral MVCs in bilateral tasks. Elbow flexion force and biceps surface electromyogram (EMG) were measured bilaterally. Proportionally increased EMG activity on the contralateral limb (motor overflow) was observed during unilateral tasks of the nonimpaired limb but not of the impaired limb. During bilateral tasks at submaximal levels, the impaired limb produced less force (i.e., force deficit [FD]) as compared to expected forces based upon its unilateral MVC. Force deficit on the impaired limb was compensated by greater force production on the nonimpaired limb such that the visual target was reached. However, force contribution to the total force progressively decreased from the nonimpaired side, when the level of submaximal contractions increased. During bilateral MVC tasks, there was no FD on the impaired limb, but FD was observed on the nonimpaired limb. A net result of a small bilateral deficit in force with parallel changes in EMG was observed. These novel findings of activation level–dependent interactions and asymmetrical contralateral motor overflow provide new insights that, among other compensatory mechanisms, ipsilateral corticospinal projections from the nonlesioned hemisphere play an important role in interlimb interactions in chronic stroke, in addition to unbalanced interhemispheric inhibition.

Gravitational force modulates muscle activity during mechanical oscillation of the tibia in humans

Mechanical oscillation (vibration) is an osteogenic stimulus for bone in animal models and may hold promise as an anti-osteoporosis measure in humans with spinal cord injury (SCI). However, the level of reflex induced muscle contractions associated with various loads (g force) during limb segment oscillation is uncertain. The purpose of this study was to determine whether certain gravitational loads (g forces) at a fixed oscillation frequency (30 Hz) increases muscle reflex activity in individuals with and without SCI. Nine healthy subjects and two individuals with SCI sat with their hip and knee joints at 90° and the foot secured on an oscillation platform. Vertical mechanical oscillations were introduced at 0.3, 0.6, 1.2, 3 and 5 g force for 20 s at 30 Hz. Non-SCI subjects received the oscillation with and without a 5% MVC background contraction. Peak soleus and tibialis anterior (TA) EMG were normalized to M-max. Soleus and TA EMG were <2.5% of M-max in both SCI and non-SCI subjects. The greatest EMG occurred at the highest acceleration (5 g). Low magnitude mechanical oscillation, shown to enhance bone anabolism in animal models, did not elicit high levels of reflex muscle activity in individuals with and without SCI. These findings support the g force modulated background muscle activity during fixed frequency vibration. The magnitude of muscle activity was low and likely does not influence the load during fixed frequency oscillation of the tibia.

Limb segment vibration modulates spinal reflex excitability and muscle mRNA expression after spinal cord injury

OBJECTIVE We investigated the effect of various doses of vertical oscillation (vibration) on soleus H-reflex amplitude and post-activation depression in individuals with and without SCI. We also explored the acute effect of short-term limb vibration on skeletal muscle mRNA expression of genes associated with spinal plasticity. METHODS Six healthy adults and five chronic complete SCI subjects received vibratory stimulation of their tibia over three different gravitational accelerations (0.3g, 0.6g, and 1.2g) at a fixed frequency (30Hz). Soleus H-reflexes were measured before, during, and after vibration. Two additional chronic complete SCI subjects had soleus muscle biopsies 3h following a single bout of vibration. RESULTS H-reflex amplitude was depressed over 83% in both groups during vibration. This vibratory-induced inhibition lasted over 2min in the control group, but not in the SCI group. Post-activation depression was modulated during the long-lasting vibratory inhibition. A single bout of mechanical oscillation altered mRNA expression from selected genes associated with synaptic plasticity. CONCLUSIONS Vibration of the lower leg inhibits the H-reflex amplitude, influences post-activation depression, and alters skeletal muscle mRNA expression of genes associated with synaptic plasticity. SIGNIFICANCE Limb segment vibration may offer a long term method to reduce spinal reflex excitability after SCI.

Repetitive Eccentric Muscle Contractions Increase Torque Unsteadiness in the Human Triceps Brachii

Torque steadiness and low-frequency fatigue (LFF) were examined in the human triceps brachii after concentric or eccentric fatigue protocols. Healthy young males (n=17) performed either concentric or eccentric elbow extensor contractions until the eccentric maximal voluntary torque decreased to 75% of pre-fatigue for both (concentric and eccentric) protocols. The number of concentric contractions was greater than the number of eccentric contractions needed to induce the same 25% decrease in eccentric MVC torque (52.2+/-2.9 vs. 41.5+/-2.1 for the concentric and eccentric protocols, respectively, p<.01). The extent of peripheral fatigue was approximately 12% greater after the concentric compared to the eccentric protocol (twitch amplitude), whereas LFF (increase in double pulse torque/single pulse torque), was similar across protocols. Steadiness, or the ability for a subject to hold a submaximal isometric contraction, was approximately 20 % more impaired during the Ecc protocol (p=.052). Similarly, the EMG activity required to hold the torque steady was nearly 20% greater after the eccentric compared to concentric protocol. These findings support that task dependent eccentric contractions preferentially alter CNS control during a precision based steadiness task.