Combined Functional Electrical Stimulation (FES) and Robotic System Driven by User Intention for Post-Stroke Wrist Rehabilitation - Biomechatronics in Medicine and Healthcare - page 113

8 6

ECR

FCR

5

6

4

4

3

6 8

TRI

BIC

6

4 4

m5f5 m1f1 m0f1 m0f0 m1f0 m5f5 m1f1 m0f1 m0f0 m1f0

Figure 8.5 The EMG activation levels of the muscles of FCR, ECR, BIC, and TRI during the
tracking tasks with different FES and robot assistive combinations and different tracking
speeds(circlesarefor10 ◦ /s, deltas are for 20 ◦ /s).

from the FES and robot parts the overall tracking performance could be improved,
in comparison with those no system support at all or the pattern with only FES
assistance.
Figure 8.5 shows the EMG activation levels of the antagonist muscle pairs
related to the wrist and the elbow joints. It was found that the EMG activation
levels of the FCR muscle in tracking tasks with FES assistance were higher than
those without FES. It was because that during electrical stimulation on the FCR,
evoked muscular potentials, i.e., M waves, besides the voluntary EMG would be
detected. However, higher ECR EMG activation levels during assistive patterns
with FES (m5f5, m1f1, m0f1) were not observed in this study, especially in the cases
with the tracking speed of 20 ◦ /s. In the experiment, most of the subjects had more
difficulties in following the tracking target moving with 20 ◦ /s than with 10 ◦ /s.
The subjects always paused in tracking when they felt hard to follow the target
cursor in trials with 20 ◦ /s. It could be a reason for the lowered EMG activation
level in tracking with 20 ◦ /s even with FES assistance. This was also associated
with the worse tracking performance measured with the RMSE and the maximal
ROM. The EMG activation levels for the BIC muscle were lowered in the assistive
patterns with FES (m5f5, m1f1, m0f1) compared to the patterns of m1f0 and m0f0,
which implied that the elbow flexor was relaxed in the wrist tracking, whereas the
pure robot-assisted tracking could not lower down the activity in the elbow flexor.
The reduced BIC activations when introducing FES assistance also resulted in
a decrease in co-contraction indexes in the muscle pairs of FCR&BIC and ECR&BIC
during the tracking ( Figure 8.6 ) . A reduction in co-contraction index of a muscle
pair mainly reflected the decrease of overlap in the contracting phase for the two