Abstract
The effects of continuous low-frequency electrical stimulation of rat muscles were studied using four different stimulation patterns at an earlier stage of stimulation. A stimulator was implanted in the rat body, and electrodes were connected directly to the peroneus longus (PL) muscle belly on the left side of the rat. The stimulator was controlled by magnetic transmission from outside the rat cage. The left PL muscle was stimulated electrically 24 hours per day for 1 week. Sixty-three rats were divided into 6 groups as follows: one group (11 rats) was stimulated with a uniform 10-Hz pattern; the second group (11 rats) was stimulated with 10 pulses at 20Hz every second (20-Hz stimulation pattern); the third group (8 rats) was stimulated with 10 pulses at 20Hz and 10 pulses at 10Hz every 2 seconds; and the fourth group (11 rats) was stimulated with a non-uniform, random pattern that had a mean frequency of 11.6Hz and ranged up to 20Hz. The total number of pulses per day was the same in all stimulation patterns except the random pattern. Both the group of 11 rats with implanted electrodes and the group of 11 without implanted electrodes were not stimulated and served as control groups. There were no significant differences among the groups in mean wet weight, twitch contraction time and half-relaxation time of single-twitch contraction, single twitch and maximum tetanic force. The fatigue indexes of the stimulated groups were significantly lower as compared with the control groups; this indicated increased resistance to fatigue. There were significant changes among the stimulated groups, and the 20-Hz stimulation pattern had a stronger improvement in fatigability than did the other patterns. Histochemical examinations using ATPase staining showed that there were no differences in fiber type composition and no differences in the cross-sectional area among the four stimulated groups and in the control group with implanted electrodes. The results showed that the low-frequency stimulation patterns produced a significant improvement in rat PL muscle fatigability without a significant change in the cross-sectional area or the composition of each fiber type; and the 20-Hz stimulation pattern could induce a more marked improvement in fatigability.
