The Relationships Among Isokinetic Endurance, Initial Strength Level, and Fiber Type

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Abstract
Knee extension isokinetic peak torque was assessed at angular velocities of 0, 30, 180, and 240[ddot]/sec, and isokinetic endurance was assessed by 50 consecutive contractions at 180[ddot]/sec in eight college age men. Also, muscle fiber type of the vastus lateralis was determined and related to isokinetic strength and fatigability. To determine the influence of initial strength on isokinetic endurance the 50 serial isokinetic contractions were assessed after subjects performed two bicycle exercise regimens designed to affect initial strength levels. Neither isokinetic peak torques (made relative to MVC or per Kg of body weight) nor the amount of strength loss over the 50 contractions correlated with fiber type. The peak torques at 180[ddot]/sec at the start of the 50 contractions differed over the three conditions (unfatigued and after the two bicycle exercise regimens), however, the amount of of strength loss over the 50 trials was similar for the three conditions. Also, the patterns of the three isokinetic fatigue curves were remarkably similar. Thus, the initial strength level across the treatments did not affect the rate of fatigue. However, when the treatment conditions were examined separately, the amount of strength loss over the 50 trials correlated significantly with initial strength. Thus, factors other than, or in addition to, fiber type and initial strength level must influence the rate of isokinetic fatigue.