Serial isometric contractions under imposed myotatic stretch conditions in high-strength and low-strength men.

The immediate effects of an imposed myotatic stretch on knee extensor force were studied in 12 high-strength and 12 low-strength men. Under nonfatigued pre-exercise conditions, significant tension increases of 6.5% for the high-strength group and 11.0% for low-strength subjects were observed as a result of the imposed stretch. An exercise treatment involving 28 serial isometic contractions, each of 5 s duration, with an intertrial rest period of 10 s was administered. This fatiguing exercise resulted in significant decrements in strength on the order of 28.0% and 18.5% for the high-strength and low-strength groups, respectively. A Similar treatment which included a 1 s imposed myotatic stretch during each trial resulted in a greater strength decrement for the low-strength group (26.4%) than for the high-strength subjects (15.0%). A neural factor involving the stretch reflex is tentatively suggested as a plausible explanation accounting for the observation that high-strength subjects fatigue faster than low-strength subjects under conditions of isometric exercise, while low-strength subjects fatigue faster than high-strength individuals in isometric exercise which is performed with an imposed stretch.