Fatigue Response in Human Quadriceps Femoris Muscle during High Frequency Electrical Stimulation*.

The purpose of this study was to examine the fatigue response of the quadriceps femoris muscle to two patterns of high frequency alternating electrical current. Muscle fatigue was evaluated by the comparison of isometric torque fluctuations during the 10-minute application of both stimulus patterns. Muscle fatigue was also assessed during an isokinetic fatigue test which immediately followed both stimulation patterns. The results indicated that greater amounts of electrical stimulation produced lower current-induced contraction intensities with a greater amount of fatigue. During the isokinetic fatigue test, smaller (P < 0.01) exponential peak torque declines were observed following greater amounts of electrical stimulation. This suggested that high frequency current may selectively fatigue fast twitch (FT) muscle fibers. Therefore, it was concluded that selective stimulation of FT muscle fibers may be an important component explaining the mechanism of strength increases following application of high frequency alternating current. J Orthop Sports Phys Ther 1986;7(4):145-153.