Involuntary paretic wrist/finger flexion forces and EMG increase with shoulder abduction load in individuals with chronic stroke

Abstract Background After stroke, motor control is often negatively affected, leaving survivors with less muscle strength and coordination, increased tone, and abnormal synergies (coupled joint movements) in their affected upper extremity. Humeral internal and external rotation have been included in definitions of abnormal synergy but have yet to be studied in-depth. Objective Determine the ability to generate internal and external rotation torque under different shoulder abduction and adduction loads in persons with chronic stroke (paretic and non-paretic arm) and uninjured controls. Methods 24 participants, 12 with impairments after stroke and 12 controls, completed this study. A robotic device controlled abduction and adduction loading to 0, 25, and 50% of maximum strength in each direction. Once established against the vertical load, each participant generated maximum internal and external rotation torque in a dual-task paradigm. Four linear mixed-effects models tested the effect of group (control, non-paretic, and paretic), load (0, 25, 50% adduction or abduction), and their interaction on task performance; one model was created for each combination of dual-task directions (external or internal rotation during abduction or adduction). The protocol was then modeled using OpenSim to understand and explain the role of biomechanical (muscle action) constraints on task performance. Results Group was significant in all task combinations. Paretic arms were less able to generate internal and external rotation during abduction and adduction, respectively. There was a significant effect of load in three of four load/task combinations for all groups. Load-level and group interactions were not significant, indicating that abduction and adduction loading affected each group in a similar manner. OpenSim musculoskeletal modeling mirrored the experimental results of control and non-paretic arms and also, when adjusted for weakness, paretic arm performance. Simulations incorporating increased co-activation mirrored the drop in performance observed across all dual-tasks in paretic arms. Conclusion Common biomechanical constraints (muscle actions) explain limitations in external and internal rotation strength during adduction and abduction dual-tasks, respectively. Additional non-load-dependent effects such as increased antagonist co-activation (hypertonia) may cause the observed decreased performance in individuals with stroke. The inclusion of external rotation in flexion synergy and of internal rotation in extension synergy may be over-simplifications.

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Abstract TP147: Quantitative Measures of Strength and Synergy Differentiate Individuals With Chronic Stroke With and Without Clinically Detectable Elbow Contracture

Stroke ◽

10.1161/str.51.suppl_1.tp147 ◽

2020 ◽

Vol 51 (Suppl_1) ◽

Author(s):

Grace C Bellinger ◽

Michael D Ellis

Keyword(s):

Quantitative Measure ◽

Chronic Stroke ◽

Future Research ◽

Emg Activity ◽

Shoulder Abduction ◽

Joint Control ◽

Elbow Extension ◽

Unaffected Side ◽

Elbow Contracture ◽

Flexion Synergy

Many individuals with chronic stroke demonstrate contracture of the elbow flexors. The development of contracture may be attributable to underlying impairments such as weakness, flexion synergy, and hyperactive reflexes. This study explored differences in motor impairment and function between 17 individuals with clinically detectable elbow flexor contracture and 17 individuals with full passive range of motion. The groups did not differ in age (61.61 ± 7.99, 55.06 ± 12.48, p = 0.078), years post-stroke (12.92 ± 9.34, 10.60 ± 7.16, p = 0.423), or Fugl-Meyer Motor Assessment score (FMA, 26.35 ± 5.86, 26.47 ± 8.70, p = 0.963). The passive range limitation in the contracture group was 3 to 36° (11.65 ± 8.30°). Kinetics, kinematics, and EMG were used to quantify four motor impairments and reaching function. Shoulder abduction and elbow extension strength were measured isometrically and normalized to the unaffected side. Flexion synergy was quantified as a force-based measure assessing independent joint control. Flexor spasticity was quantified while reaching at 50% of maximum shoulder abduction as the change in biceps EMG from reach onset to peak angular velocity, normalized by maximal EMG activity. Reaching function was defined as maximum reaching distance against gravity and normalized by target distance (-10° of full extension). The groups differed in elbow extension strength (Contracture, 0.315 ± 0.129; No contracture, 0.559 ± 0.153; p < 0.001) and flexion synergy (0.146 ± 0.186, 0.397 ± 0.229, p = 0.009). The groups did not differ in shoulder abduction strength (0.500 ± 0.174, 0.615 ± 0.199, p = 0.080), flexor spasticity (0.079 ± 0.090, 0.056 ± 0.115, p = 0.523), or reaching function (0.501 ± 0.391, 0.714 ± 0.296, p = 0.082). The findings of this study suggest a relationship between elbow contracture and the concurrent presence of elbow extension weakness and flexion synergy. The quantitative measure of reaching function will likely differentiate individuals with and without contracture if the assessment is modified so that the standardized reaching target is located at 0° of elbow extension (normal range). Future research should use quantitative metrics to further explore the temporal recovery of impairments in order to prevent the development of contracture.

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The effect of transcranial direct current stimulation on the expression of the flexor synergy in the paretic arm in chronic stroke is dependent on shoulder abduction loading

Frontiers in Human Neuroscience ◽

10.3389/fnhum.2015.00262 ◽

2015 ◽

Vol 9 ◽

Cited By ~ 12

Author(s):

Jun Yao ◽

Justin Drogos ◽

Fleur Veltink ◽

Caitlyn Anderson ◽

Janny Concha Urday Zaa ◽

...

Keyword(s):

Direct Current ◽

Transcranial Direct Current Stimulation ◽

Chronic Stroke ◽

Shoulder Abduction ◽

Direct Current Stimulation

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Impairment-Based 3-D Robotic Intervention Improves Upper Extremity Work Area in Chronic Stroke: Targeting Abnormal Joint Torque Coupling With Progressive Shoulder Abduction Loading

IEEE Transactions on Robotics ◽

10.1109/tro.2009.2017111 ◽

2009 ◽

Vol 25 (3) ◽

pp. 549-555 ◽

Cited By ~ 42

Author(s):

M.D. Ellis ◽

T.M. Sukal-Moulton ◽

J. Dewald

Keyword(s):

Upper Extremity ◽

Chronic Stroke ◽

Joint Torque ◽

Shoulder Abduction ◽

Work Area

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The Impact of Shoulder Abduction Loading on Volitional Hand Opening and Grasping in Chronic Hemiparetic Stroke

Neurorehabilitation and Neural Repair ◽

10.1177/1545968317697033 ◽

2017 ◽

Vol 31 (6) ◽

pp. 521-529 ◽

Cited By ~ 28

Author(s):

Yiyun Lan ◽

Jun Yao ◽

Julius P. A. Dewald

Keyword(s):

Shoulder Abduction ◽

Grasping Forces ◽

Finger Flexion ◽

Enhanced Expression ◽

Hemiparetic Stroke ◽

Chronic Hemiparetic Stroke ◽

And Control ◽

The Impact ◽

Hand Opening ◽

Flexion Synergy

Background. Up to 60% of individuals with moderate to severe chronic hemiparetic stroke experience excessive involuntary wrist/finger flexion that constrains functional hand movements including hand opening. It’s not known how stroke-induced brain injury impacts volitional hand opening and grasping forces as a result of the expression of abnormal coupling between shoulder abduction and wrist/finger flexion or the flexion synergy. Objective. The goal of this study is to understand how shoulder abduction loading affects volitional hand opening and grasping forces in individuals with moderate to severe chronic hemiparetic stroke. Methods. Thirty-six individuals (stroke, 26; control, 10) were recruited for this study. Each participant was instructed to perform maximal hand opening and grasping forces while the arm was either fully supported or lifted with a weight equal to 25% or 50% of the participant’s maximal shoulder abduction torque. Hand pentagon area, defined as the area formed by the tips of thumb and fingers, was calculated during hand opening. Forces were recorded during grasping. Results. In individuals with moderate stroke, increasing shoulder abduction loading reduced the ability to maximally open the hand. In individuals with severe stroke, who were not able to open the hand, grasping forces were generated and increased with shoulder abduction loading. Stroke individuals also showed a reduced ability to control volitional grasping forces due to the enhanced expression of flexion synergy. Conclusions. Shoulder abduction loading reduced the ability to volitionally open the hand and control grasping forces after stroke. Neural mechanisms and clinical implications of these findings are discussed.

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