Wearable Myoelectric Interface for Neurorehabilitation (MINT) to Recover Arm Function: a Randomized Controlled Trial

Abstract

Background: Abnormal muscle co-activation contributes to arm impairment after stroke. This single-blind, randomized, sham-controlled trial evaluated the feasibility and efficacy of home-based, personalized myoelectric interface for neurorehabilitation (MINT) conditioning to reduce abnormal co-activation and enhance arm function and determine the optimal number of abnormally co-activating muscles to target during training.

Methods: Moderately to severely impaired chronic stroke survivors were randomized to one of three MINT groups (who played customized games requiring independent activation of 2 or 3 abnormally co-activating muscles) or a sham control group (played using one muscle). All groups trained 90 minutes/day, 5 days/week at home and 1 day/week in lab, for 6 weeks, and changed trained muscle sets every 2-3 weeks. The primary outcome was the Wolf Motor Function Test (WMFT) at 6 weeks.

Results: Fifty-nine participants completed the training. Participants performed 315 ± 85 (mean ± SD) repetitions daily. At week 6, participants in all MINT groups combined improved by 4 s on WMFT (p=0.0008), exceeding the minimal clinically important difference (1.5 s). Participants who trained 3 muscles simultaneously improved by 6.8 s (p=0.001), while the 2-muscle and sham groups did not change significantly. In per-protocol analysis, the 3-muscle group, but not 2-muscle groups, improved significantly more than sham (p=0.046), though not in intention-to-treat analysis. All MINT groups continued improving at 4 weeks post-training. Importantly, severely impaired participants in combined MINT groups improved more than those in sham (p=0.02). Importantly, combined MINT groups also improved their reaching range of motion significantly more than sham. Co-activation decreased by 76% in MINT groups during training. Notably, reduction in co-activation during reaching correlated significantly with improved arm function and range of motion. Other secondary outcomes did not show clinically important improvement. Stroke involving the posterior limb of the internal capsule negatively predicted response to MINT.

Conclusions: Home-based MINT conditioning, especially the 3-muscle variant, is feasible, reduces co-activation, and improves arm movement and function.

Clinical trial registration―: ClinicalTrials.gov (NCT03401762).

Keywords: EMG; arm impairment; gaming; movement; myoelectric; stroke recovery; stroke rehabilitation; wearable.

Figure 1.

MINT paradigm and CONSORT diagram. (A) Top, an example stroke participant used the wearable MINT device to transmit EMGs of biceps (blue) and anterior deltoid (purple) to the laptop. Bottom, MINT software mapped EMGs of these muscles to orthogonal components of cursor movement. In the example, biceps was mapped to the right (blue arrow) and anterior deltoid was mapped up (purple arrow). When biceps and anterior deltoid were co-activated, the cursor moved along a diagonal between the two directions (green). The participant was then conditioned using MINT to decouple the two muscles; in this example, to activate biceps independently of anterior deltoid. (B) Examples of MINT game screens for the four groups. In the 2D group, participants used two muscles mapped to the x and y directions. Similarly, in the 2D Reach group, participants were trained with two muscles, but they were given additional visual prompts to encourage more effort to reach in the current muscle’s pulling direction. In the 3D group, participants used three muscles simultaneously, with each muscle separately mapped to the x, y, and z directions of cursor movement. Finally, in the 1D sham group, participants used only one muscle mapped to the x direction. (C) CONSORT enrollment flow chart.

Figure 2.

Effect of MINT conditioning on improving motor function. (A) Mean (±SE) WMFT at baseline (BL) and Week 6 (W6) for each group (red, combined experimental groups; green, 3D; blue, 2D; orange, 2D Reach; black, sham). (B) Mean change in WMFT relative to baseline. Dashed line, MCID. (C) Mean change in WMFT relative to baseline for items related only to elbow or shoulder. (D) Mean change in WMFT relative to baseline stratified by injury location for all participants. Abbreviations refer to strokes involving: PLIC, posterior limb of the internal capsule, BG, basal ganglia, CR, corona radiata. Asterisks (*) indicate p < 0.05.

Figure 3.

Effect of MINT conditioning on reaching kinematics and muscle synergies. (A) Mean changes on kinematic metrics at Week 6 relative to baseline for experimental and sham groups: Top left: Sweep area. Top right: Active range of motion for front reaching. Bottom left: Vertical reaching. Bottom right: Side reaching. (B) Mean (±SE) disparity index (DI) at Weeks 0 and 6 for responder (Top) and sham (Bottom) participants for each pair of trained muscles. (C) Correlations between changes in DI and changes in (Top) AROM during combined front and vertical reach and (Bottom) WMFT for combined experimental and sham groups. *, p<0.05