The purpose of this study was to evaluate continuous concentric (CON) and eccentric (ECC) isokinetic loading of the knee extensors (KE) and flexors (KF) in power athletes (PA), aerobically trained runners (ATR), and moderately active individuals (MAI). Sixty subjects, aged 18–35 years with no previous history of lower extremity muscle or joint injury, were placed in one of the three groups based on physiologic assessment. Gravity corrected CON and ECC average isokinetic torque was measured at 75–30° of knee flexion at angular velocities of 90°/s, 135°/s, and 180°/s. Analysis of variance was computed for each contraction type and for the calculated KF-E ratios. The PA group produced significantly greater average CON and ECC torque than either ATR or MAI (p < 0.01) for both the KE and KF, whereas the ATR and MAI groups did not significantly differ. For all groups, isokinetic KE CON and ECC torque was significantly greater than that produced by the KF at each velocity examined (p < 0.01). ECC KF-E ratios were significantly greater (p < 0.01) than CON ratios for each of the three groups for all velocities. The PA had significantly greater CON and ECC KF-E ratios (p < 0.01) than either the ATR or MAI groups, who did not differ significantly. These findings are important when designing individualized conditioning and rehabilitation programs for athletes from different disciplines.