Comparison of quadriceps isokinetic eccentric and isokinetic concentric data using a standard fatigue protocol

The purpose of the study was to compare fatigue development in concentric vs. eccentric muscular activation in the quadriceps of 15 healthy human subjects, controlling as many of the dynamic variables as possible. An isokinetic testing protocol was used, with knee joint angular velocity limited to 180 deg/sec, and with 40 repetitions through a range of motion of 75 deg constituting the fatigue-developing exercise. Quadriceps torque was measured via a robotic dynamometer, IEMG of the rectus femoris muscle was recorded, and a subjective pain rating scale was used to assess delayed muscle soreness following fatiguing exercise for concentric and eccentric tests. Eccentric peak torque to body weight ratio was greater than the concentric ratio (1.25 vs. 0.66, p <.001), significant torque fatigue developed in both eccentric and concentric tests (30.3% and 13.7%), and significant decline in IEMG occurred in both eccentric and concentric tests (17.0% and 15.1%). The eccentric declines in torque and IEMG were not significantly different than the concentric declines. There was no clear difference in the pain reports associated with the two different exercise modes. Delayed onset muscle soreness was rated as mild (3 on scale of 10) at most during the 72-h surveillance period. It is concluded that the development of fatigue through eccentric muscular activation may stress the contractile mechanism less than that associated with concentric muscular contraction, and that standard clinical fatigue protocols may have to be modified to better distinguish the role of active neuromotor vs. musculotendinous contributions to performance test results.