Estimates of individual muscle power production in normal adult walking.

BACKGROUND: The purpose of this study was to determine the contribution of individual hip muscles to the net hip power in normal adult self-selected speed walking. A further goal was to examine each muscle's role in propulsion or support of the body during that task. METHODS: An EMG-to-force processing (EFP) model was developed which scaled muscle-tendon unit (MTU) force output to gait EMG. Active muscle power was defined as the product of MTU forces (derived from EFP) and that muscle's contraction velocity. Passive hip power was estimated from passive moments associates with hip position (angle of flexion (extension)) and the hip's angular velocity. Net hip EFP power was determined by summing individual active hip muscle power plus the net passive hip power at each percent gait cycle interval. Net hip power was also calculated for these study participants via inverse dynamics (kinetics plus kinematics, KIN). The inverse dynamics technique - well accepted in the biomechanics literature - was used as a "gold standard" for validation of this EFP model. Closeness of fit of the power curves of the two methods was used to validate the model. RESULTS: The correlation between the EFP and KIN methods was sufficiently close, suggesting validation of the model's ability to provide reasonable estimates of power produced by individual hip muscles. Key findings were that (1) most muscles undergo a stretch-shorten cycle of muscle contraction, (2) greatest power was produced by the hip abductors, and (3) the hip adductors contribute to either hip adduction or hip extension (but not both). CONCLUSIONS: The EMG-to-force processing approach provides reasonable estimates of individual hip muscle forces in self-selected speed walking in neurologically-intact adults.

An EMG-to-Force Processing approach for estimating in vivo hip muscle forces in normal human walking.

The force of a single muscle is not directly measurable without invasive methods. Yet invasive techniques are not appropriate for clinical use, thus a non-invasive technique that combined the electromyographic (EMG) signal and a neuromuscular model was developed to determine in vivo active muscle forces at the hip. The EMG-to-force processing (EFP) model included active and passive moment components, and the net EFP moment was compared with the hip moment obtained with standard inverse dynamics techniques ("gold standard"). The two methods were compared at percent gait cycle intervals, and the correlation coefficient between methods was excellent (r2=91). The closeness of fit confirms that the approach is a reasonable approximation of net moment and, possibly, individual muscle forces. The greatest estimated hip force was produced by a hip abductor. A novel finding was that the hip adductors did not behave a single synergistic group. The Adductor Magnus synergistically assisted other hip extensors, and produced forces that were out-of-phase with the other hip adductor forces. Rectus Femoris was only active during hip flexion (not knee extension).

Error augmentation enhancing arm recovery in individuals with chronic stroke: a randomized crossover design.

BACKGROUND: Neurorehabilitation studies suggest that manipulation of error signals during practice can stimulate improvement in coordination after stroke. OBJECTIVE: To test visual display and robotic technology that delivers augmented error signals during training, in participants with stroke. METHODS: A total of 26 participants with chronic hemiparesis were trained with haptic (via robot-rendered forces) and graphic (via a virtual environment) distortions to amplify upper-extremity (UE) tracking error. In a randomized crossover design, the intervention was compared with an equivalent amount of practice without error augmentation (EA). Interventions involved three 45-minute sessions per week for 2 weeks, then 1 week of no treatment, and then 2 additional weeks of the alternate treatment. A therapist provided a visual cursor using a tracking device, and participants were instructed to match it with their hand. Haptic and visual EA was used with blinding of participant, therapist, technician-operator, and evaluator. Clinical measures of impairment were obtained at the beginning and end of each 2-week treatment phase as well as at 1 week and at 45 days after the last treatment. RESULTS: Outcomes showed a small, but significant benefit to EA training over simple repetitive practice, with a mean 2-week improvement in Fugl-Meyer UE motor score of 2.08 and Wolf Motor Function Test of timed tasks of 1.48 s. CONCLUSIONS: This interactive technology may improve UE motor recovery of stroke-related hemiparesis.

Mapping the neglected space: gradients of detection revealed by virtual reality.

BACKGROUND: Spatial neglect affects perception along different dimensions. However, there is limited availability of 3-dimensional (3D) methods that fully map out a patient's volume of deficit, although this could guide clinical management. OBJECTIVE: To test whether patients with neglect exhibit simple contralesional versus complex perceptual deficits and whether deficits are best described using Cartesian (rectangular) or polar coordinates. METHODS: Seventeen right-hemisphere persons with stroke (8 with a history of neglect) and 9 healthy controls were exposed to a 3D virtual environment. Targets placed in a dense array appeared one at a time in various locations. RESULTS: When tested using rectangular array of targets, subjects in the neglect group exhibited complex asymmetries across several dimensions in both reaction time and target detection rates. Paper-and-pencil tests only detected neglect in 4 of 8 of these patients. When tested using polar array of targets, 2 patients who initially appeared to perform poorly in both left and near space only showed a simple left-side asymmetry that depended almost entirely on the angle from the sagittal plane. A third patient exhibited left neglect irrespective of the arrangements of targets used. An idealized model with pure dependence on the polar angle demonstrated how such deficits could be misconstrued as near neglect if one uses a rectangular array. CONCLUSIONS: Such deficits may be poorly detected by paper-and-pencil tests and even by computerized tests that use regular screens. Assessments that incorporate 3D arrangements of targets enable precise mapping of deficient areas and detect subtle forms of neglect whose identification may be relevant to treatment strategies.

Effect of a serotonin antagonist on delay in grip muscle relaxation for persons with chronic hemiparetic stroke.

OBJECTIVE: To investigate if, following stroke, sustained involuntary activity after voluntary contraction (e.g., grip) of the long finger flexor muscles of the paretic hand is attributable to augmented serotonin release from brainstem pathways, affecting excitability of spastic motoneurons. METHODS: This single-dose placebo-controlled study examined whether a serotonin receptor (5-HT2) antagonist, cyproheptadine hydrochloride, could reduce delay in muscle relaxation of a key paretic long finger flexor muscle immediately after grip for persons with stroke. Time to initiate the long finger flexor muscle contraction, grip and pinch strengths, and clinical hand function scores (the Action Research Arm Test and the Box and Block Test) were also assessed. RESULTS: Cyproheptadine hydrochloride reduced mean delays in finger relaxation (n=13; from 7.2 to 4.1 s; SEM=1.2 s; p=.026) in comparison to placebo, while leaving grip and pinch strengths and time to initiate the muscle contraction largely unaffected. Reduction in the relaxation time alone did not lead to increased clinical hand function scores. CONCLUSIONS: The findings support the supposition that monoaminergic brainstem pathways may be disinhibited following stroke, thereby resulting in increased delays in muscle relaxation. SIGNIFICANCE: Treatments to reduce delay in muscle relaxation may facilitate hand rehabilitation in persons with stroke.

Use of visual force feedback to improve digit force direction during pinch grip in persons with stroke: a pilot study.

OBJECTIVE: To investigate whether visual feedback of digit force directions for the index fingertip and thumb tip during repeated practice of grip force production can correct the digit force directions for persons with stroke during grip assessments. Following stroke, the paretic fingers generate digit forces with a higher than normal proportion of shear force to compression force during grip. This misdirected digit force may lead to finger-object slip and failure to stably grasp an object. DESIGN: A case series. SETTING: Laboratory. PARTICIPANTS: Persons (N=11) with severe chronic hand impairment after stroke. INTERVENTIONS: Four training sessions during which participants practiced directing the index finger and thumb forces in various target directions during pinch using visual feedback. MAIN OUTCOME MEASURE: Digit force direction during pinch and clinical hand function scores were measured before and immediately after the training. RESULTS: Study participants were able to redirect the digit force closer to the direction perpendicular to the object surface and increase their hand function scores after training. The mean ratio of the shear force to the normal force decreased from 58% to 41% (SD, 17%), the mean Box and Block Test score increased from 1.4 to 3.4 (SD, 2.0), and the mean Action Research Arm Test score increased from 10.8 to 12.1 (SD, 1.3) (P<.05 for all 3 measures). CONCLUSIONS: Repeated practice of pinch with visual feedback of force direction improved grip force control in persons with stroke. Visual feedback of pinch forces may prove valuable as a rehabilitation paradigm for improving hand function.

Stroke and neurodegenerative disorders. 1. Acute stroke evaluation, management, risks, prevention, and prognosis.

UNLABELLED: This self-directed learning module highlights recent developments in the acute care of stroke patients, prediction of outcome after stroke, evaluation of risk factors, secondary prevention of stroke, and the evaluation of the young adult with stroke. It is part of the study guide on stroke and neurodegenerative disorders in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. This article contains sections on the acute evaluation and management of the stroke patient, prediction of functional outcome after stroke, and secondary prevention of stroke. Special emphasis is given to the evaluation of the young adult with stroke. OVERALL ARTICLE OBJECTIVES: (a) To summarize the acute evaluation and management of stroke, particularly in the young stroke patient; and (b) to review the risk factors for stroke and secondary prevention measures.

Stroke and neurodegenerative disorders. 2. Stroke: comorbidities and complications.

UNLABELLED: This self-directed learning module highlights diagnosis and treatment of comorbidities and complications encountered by patients with stroke. It is part of the study guide on stroke and neurodegenerative disorders in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. This article specifically focuses on cardiopulmonary complications and examines neurologic sequelae, risk factors for falls, and prevention strategies. It also discusses upper-limb pain, fatigue, and depression and highlights diagnosis and management of genitourinary complications. OVERALL ARTICLE OBJECTIVE: To summarize common comorbidities and complications encountered by patients after stroke.

Stroke and neurodegenerative disorders. 3. Stroke: rehabilitation management.

UNLABELLED: This self-directed learning module highlights common rehabilitation issues in stroke survivors. Topics include spasticity, constraint-induced movement therapy, partial body weight-supported treadmill training, virtual reality training, vestibular retraining, aphasia treatment, and cognitive retraining. It is part of the study chapter on stroke and neurodegenerative disorders in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. OVERALL ARTICLE OBJECTIVES: (a) To identify and review the treatment options for poststroke spasticity; (b) to review the use of body weight-supported treadmill training in stroke patients; (c) to describe virtual reality training as an adjunct in stroke rehabilitation; (d) to review vestibular rehabilitation; (e) to discuss advances in aphasia treatment; (f) to discuss cognitive retraining; and (g) to provide an update on treatment of neglect syndromes.

Stroke and neurodegenerative disorders. 4. Neurodegenerative disorders.

UNLABELLED: This self-directed learning module highlights diagnosis, treatment, and rehabilitation issues in patients with neurodegenerative disorders, including multiple sclerosis (MS), Parkinson's disease, and amyotrophic lateral sclerosis (ALS). It is part of the study guide on stroke and neurodegenerative disorders in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. This article specifically focuses on the differential diagnosis, diagnostic evaluation, medical management, and rehabilitation issues in MS. Similarly, the differential diagnosis treatment and rehabilitation in Parkinson's disease is discussed. Electrodiagnosis, pharmacologic treatment, and rehabilitation options for ALS are also discussed. OVERALL ARTICLE OBJECTIVES: To review the differential diagnosis, evaluation, medical treatment, and rehabilitation management of patients with MS, Parkinson's disease, and ALS.

Rehabilitation of movement disorders.

UNLABELLED: This self-directed learning module highlights several movement disorders. These include dystonia, chorea, tremors, and myoclonus. A description of the clinical presentation and associated disease processes is presented. Although the discussion on treatment focuses on pharmacologic intervention, surgical options are presented when appropriate. Other movement disorders (ie, parkinsonism) are discussed elsewhere in the Study Guide. OVERALL ARTICLE OBJECTIVES: (a) To define the various symptoms and etiologies of dystonia; (b) to define chorea and its treatment; (c) to define tremors, including associated neurologic disorders, plus pharmacologic and potential surgical interventions; and (d) to describe the symptoms, classification, and treatment of primary and secondary myoclonus.