Nonlinear analysis of electromyogram following 3 gait training with myoelectrically triggered 4 neuromuscular electrical stimulation in stroke 5 survivors

8 Neuromuscular electrical stimulation (NMES) facilitates ambulatory function after paralysis by activating the muscles 9 of the lower extremities. The NMES-assisted stepping can either be triggered by a heel-switch (switch-trigger), or by 10 an electromyogram (EMG)-based gait event detector (EMG-trigger). The command sources—switch-trigger or 11 EMG-trigger—were presented to each group of six chronic (>6 months post-stroke) hemiplegic stroke survivors. 12 The switch-trigger group underwent transcutaneous NMES-assisted gait training for 1 h, five times a week for 13 2 weeks, where the stimulation of the tibialis anterior muscle of the paretic limb was triggered with a heel-switch 14 detecting heel-rise of the same limb. The EMG-trigger group underwent transcutaneous NMES-assisted gait training 15 of the same duration and frequency where the stimulation was triggered with surface EMG from medial 16 gastrocnemius (MG) of the paretic limb in conjunction with a heel-switch detecting heel-rise of the same limb. 17 During the baseline and post-intervention surface EMG assessment, a total of 10 s of surface EMG was recorded 18 from bilateral MG muscle while the subjects tried to stand steady on their toes. A nonlinear tool—recurrence 19 quantification analysis (RQA)—was used to analyze the surface EMG. The objective of this study was to find the 20 effect of NMES-assisted gait training with switch-trigger or EMG-trigger on two RQA parameters—the percentage of 21 recurrence (%Rec) and determinism (%Det), which were extracted from surface EMG during fatiguing contractions 22 of the paretic muscle. The experimental results showed that during fatiguing contractions, (1) %Rec and %Det have 23 a higher initial value for paretic muscle than the non-paretic muscle, (2) the rate of change in %Rec and %Det was 24 negative for the paretic muscle but positive for the non-paretic muscle, (3) the rate of change in %Rec and %Det 25 significantly increased from baseline for the paretic muscle after EMG-triggered NMES-assisted gait training. 26 Therefore, the study showed an improvement in paretic muscle function during a fatiguing task following gait 27 training with EMG-triggered NMES. This study also showed that RQA parameters—%Rec and %Det—were sensitive 28 to changes in paretic/non-paretic muscle properties due to gait training and can be used for non-invasive muscle 29 monitoring in stroke survivors undergoing rehabilitation.