Fig. 2.

A gating algorithm for optical data acquisition during electrical stimulation (ES) at 2 Hz. The outputs from channel #1 (CH1) (a) and channel #2 (CH2) (c) of muscle stimulator were synchronized; thus the muscle status (contraction or relaxation) controlled by CH2 could be read from the CH1 output (“2 s on” or “2 s off”). A digital counter in the A/D board was used to detect the ES pulses generated from CH1. The pulse counts increased continuously when ES was on and remained unchanged when ES was off (b). Optical data were recorded within 1.5 s when the ES was off (d).