FIG. 4.

Characteristics of spinal stimulation during quiet sitting. (A) Electromyography (EMG) recordings of four trunk muscles from a representative participant (P2) without (blue) and with (red) submotor threshold stimulation during unsupported quiet sitting. The external obliques (Obl), rectus abdominis (RA), erector spinae at levels T7 (E-T7) and L3 (E-L3), and rectus femoris (RF) are shown. (B) Spinal alignment (left), mean trunk curvature (middle), and trunk angle (right) during quiet sitting without (blue) and with (red) spinal stimulation. A 5 sec window was used (4–9 sec after trial onset) to determine the mean trunk curvature, horizontal distance between the hip (anterior-superior iliac crest), and maximal trunk displacement during quiet upright sitting. The pelvis is assumed to be fixed at the origin. Higher values in trunk curvature indicate a decrease in trunk extension and more kyphotic (C-shaped) sitting. Higher values of trunk angle indicate more upright sitting. Individual data for all participants are shown via symbols. *statistical significance, two-tailed nonparametric Wilcoxon signed-rank test, in which n = 8 and α < 0.05.