Isotonic preload versus isokinetic knee extension resistance training.

To examine training (3 d.wk-1 for 6 wk) differences using active robotic isotonic and isokinetic concentric knee extension resistance on full range of motion (ROM) (90 degrees to 0 degree of flexion) strength development and power, 22 men and 10 women were randomly assigned to either an isotonic, isokinetic, or control group. The isotonic group exercised using a preload resistance that was initially set at 25% of peak isometric torque and then increased 5 N.m each week. The isokinetic group exercised at 120, 150, 180, and 210 degrees.s-1 using a velocity spectrum protocol. Before and after training, isotonic power (W), isokinetic power (W) at speeds of 120 degrees.s-1, 150 degrees.s-1, 180 degrees.s-1, and 210 degrees.s-1, and isometric torques (N.m) at 10 degrees, 30 degrees, 50 degrees, 70 degrees, and 90 degrees of knee flexion were measured. Analysis of variance using repeated measures showed: 1) isotonic is superior to isokinetic resistance training in terms of increasing muscle strength (P < 0.05) and power (P < 0.05); 2) isotonic preload knee extension resistance training elicits full ROM strength development (P < 0.05); and 3) power (P < 0.05) increases are specific to isotonic training despite the testing mode.