EFFECTS OF ALTERING PARAMETERS FOR ELECTRICAL STIMULATION ON CUTANEOUS REFLEXES IN HUMAN INTRINSIC HAND MUSCLE / 体力科学

ABSTRACT

The present study investigated an effective method of eliciting medium and long latency cutaneous reflexes in normal human subjects. The effect of changes in stimulus conditions (number of pulse train, duration of electrical pulse and inter-stimulus interval) on cutaneous reflexes in the first dorsal interosseous muscle (FDI) following non-noxious electrical stimulation to the hand digits (digit 1 ; D1, digit 2 ; D2 and digit 5 ; D5) were investigated in seven healthy volunteers. Cutaneous reflexes were elicited while the subjects performed isolated isometric contraction of FDI (D2 abduction). Under all experimental conditions, the level of muscle contraction was set at 10% of the maximal EMG amplitude, which was determined during maximal voluntary contraction. Intensity of the electrical stimulation was set at 2.0 times the perceptual threshold under all experimental conditions.Although the amplitude of E2 (excitatory response, peak latency ∼60∼90 ms) was independent of the number of pulses (1, 2, 3, and 5 pulses, pulse frequency at 333 Hz), that of I1 (inhibitory response, ∼45∼60 ms), I2 (inhibitory response, ∼90∼120 ms) and E3 (excitatory response, ∼120∼180 ms) was significantly increased depending on the number of pulses (p<0.001). Amplitudes of E2 and I2 were significantly affected by the digit stimulated (p<0.01). For all four components of the cutaneous reflexes, there were no significant differences in magnitude even by alternating both the inter-stimulus interval (fixed at 1, 2 and 3 Hz and random between at 0.7 and 2 Hz) and the duration (0.1, 0.5 and 1 ms) of the electrical stimulation.These findings suggest that the susceptibility of responsible interneurons impinging on each reflex pathway to temporal summation of the test impulse differs depending on the digit stimulated. It is also likely that almost the same population of the cutaneous afferent fibers were activated by test stimulation with different durations as far as the same stimulus intensity was utilized. As a practical application, double or more pulses up to 3 Hz without causing pain is recommended to effectively evoke medium and long latency cutaneous reflexes in FDI, which would reduce possible effects arising from fatigue.