Table 1.
Forearm length and actual size corresponding to 2L (1/12 of the forearm length) for each of the 8 participants.
Fig 1.
Coordinate system established for the determination of stimulation points of the finger extension and flexion.
Fig 2.
Stimulation points were affected by two factors and its corresponding finger angles.
(A) The effect of stimulation point displacement relative to the skin on the finger activation threshold and the selective range of each individual finger were investigated. (B) The negative electrode was placed at distances of 0L, 1L, 1.414L, and 2L away from the center of the original electrode to study whether different electrode positions caused the changes in the activation threshold and selective activation range of individual fingers. (C) The IMU sensor module was used to record the 3D finger movement angle data.
Fig 3.
The angle curve of finger A in its selective current range at a stimulus point.
Note: Ta, Tb: Activation thresholds; I1 = ceil (Ta); I2 = I1+ 1; I3 = I1 + 2.
Fig 4.
Activation thresholds of several adjacent stimulus points under different forearm positions (Participant D).
Fig 5.
The positions of stimulation points for extension and flexion of each finger.
(A) Finger extension in the forearm pronation and neutral positions; (B) finger flexion in the forearm supination and neutral positions.
Fig 6.
Distributions of stimulation points for selective stimulation of each finger extension (top) and flexion (bottom).
Some stimulation points are surrounded by circles of different sizes. The selective ranges of stimulation points for selectively stimulating individual finger extension/flexion were measured by adjusting the intensity of the applied current.
Fig 7.
Activation thresholds (left) and selective ranges (right) of individual fingers.
(*) represents a difference in the activation thresholds at different electrode positions. (†) indicates a significant difference in the selective activation thresholds of fingers at the same grid point in different forearm positions. The results are shown as the means ± SD (n = 8). *, † p < 0.05 as determined by two-way analysis of variance.
Fig 8.
Trends of angle variations of the thumb MCP and IP joints.
The angles were tested in supine and neutral forearm postures.
Fig 9.
The angle variation trends of the stimulation points in the "Low", "Medium" and "High" groups.
The results are expressed as the means (n = 8). *p < 0.05, as determined by one-way ANOVA.