The purpose of this study was to assess the fatigue and recovery of isotonic power and isometric contractile properties following task failure induced by maximal isotonic knee extensions. Using a Biodex System 3 dynamometer, thirteen men (26 ± 3 y, 179 ± 8 cm, 77 ± 9 kg) performed fatiguing isotonic (50% of isometric MVC every 1.2 s through 75 deg range of motion) single-limb knee extensions at the fastest velocity they could achieve until velocity was reduced by 35%. Recovery of power and isometric MVC were measured over 10 min. The results indicated that the time to task failure was 38 s and following task failure, power relative to baseline declined by 42 ± 4% (741.0 ± 106.0 W at baseline vs. 426.5 ± 60.3W) and MVC declined by 26 ± 5% (267.3 ± 42.5 Nm at baseline vs. 198.4 ± 45.7 Nm). Power recovered by 5 min, whereas MVC did not recover and at 10 min was only 85.1 ± 10.6% of the baseline value. Motor unit activation measured during the isometric MVC was 95.0 ± 3.7% before the fatiguing task and was unchanged at task failure (96.3 ± 2.7%) but a small amount of activation failure was apparent between 1.5 to 10 min of recovery (88.6 ± 5.2% to 91.3 ± 4.0%). Half-relaxation time measured from a 50 Hz isometric tetanus was significantly prolonged by 33.3 ± 12.6% immediately following isotonic task failure but recovered fully by 1.5 min. A significant decline in the 10:50 Hz ratio of the evoked isometric contractions was observed at 5 and 10 min of recovery. The changes in velocity and half-relaxation time during the experimental protocol were strongly and negatively correlated (r = - 0.85). It appeared that muscle contractile properties measured from isometric contractions were useful in elucidating some but not all changes in isotonic contractile performance.