Morana, C and Perrey, S. Time course of postactivation potentiation during intermittent submaximal fatiguing contrations in endurance- and power-trained athletes. J Strength Cond Res 23(5): 1456-1464, 2009-This study aimed to measure time course of postactivation potentiation during intermittent submaximal fatiguing isometric contractions in 2 groups of subjects with different physical training history. Fifteen men subjects (8 endurance-trained athletes [END] and 7 power-trained athletes [POW]) performed a 10-minute intermittent (5-second contraction, 5-second rest) knee extension exercise at 50% of their maximal voluntary isometric contraction. Mechanical (peak twitch torque, Pt) and electrophysiological (M-wave) responses following electrical stimulation of the femoral nerve were measured at rest and every 10 s throughout exercise. Vastus lateralis (VL) muscle activity (root mean square, RMS) was recorded during each contraction, and the RMS/M ratio was calculated. A significant increase in Pt (+52%, p < 0.01) was observed in both groups during the first minute of the exercise. Thereafter Pt decreased dramatically (p < 0.05) in POW whereas it remained above baseline values in END until the end of exercise. The VL RMS/M ratio increased from 7 minutes of exercise for the entire population of subjects, but showed a tendency toward greater and earlier increase in POW. Our study showed the effectiveness of an intermittent submaximal preconditioning protocol to induce similar potentiation (5-10 repetitions of 5-second submaximal contraction at 50% MVC of knee-extensors) for 2 groups of trained-individuals with different muscular profiles (END vs. POW). The enhanced fatigue resistance of endurance athletes allows the potentiating effect to prevail longer over the fatigue effect during all the 10-minute exercise. The proposed conditioning protocol (moderate-intensity, short-duration intermittent exercise) as an interesting alternative compared to MVC is adequate to warm all athletes and increase sports performance.