RYAN, ED, TW BECK, TJ HERDA, HR HULL, MJ HARTMAN, JR STOUT, and JT CRAMER. Do Practical Durations of Stretching Alter Muscle Strength? A Dose–Response Study. Med. Sci. Sports Exerc., Vol. 40, No. 8, pp. 1529–1537, 2008. To examine the time course (immediate, 10, 20, and 30 min) for the acute effects of 2, 4, and 8 min of passive stretching (PS) on isometric peak torque (PT), percent voluntary activation (% VA), EMG amplitude, peak twitch torque (PTT), rate of twitch torque development (RTD), and range of motion (ROM) of the plantarflexors. Thirteen volunteers (mean T SD age, 22 T 3 yr) participated in four randomly ordered experimental trials: control (CON) with no stretching, 2 min (PS2), 4 min (PS4), and 8 min (PS8) of PS. Testing was conducted before (pre), immediately after (post), and at 10, 20, and 30 min poststretching. The PS trials involved varied repetitions of 30-s passive stretches, whereas the CON trial included 15 min of resting. PT,% VA, EMG amplitude, PTT, and RTD were assessed during the twitch interpolation technique, whereas ROM was quantified as the maximum tolerable angle of passive dorsiflexion. PT decreased (P e 0.05) immediately after all conditions [CON (4%), PS2 (2%), PS4 (4%), and PS8 (6%)] but returned to baseline at 10, 20, and 30 min poststretching.% VA and EMG amplitude were unaltered (P 9 0.05) after all conditions. PTT and RTD decreased (P e 0.05) immediately after the PS4 (7%) and the PS8 (6%) conditions only; however, these changes were not sufficient to alter voluntary force production. There were also increases (P e 0.05) in ROM after the PS2 (8%), the PS4 (14%), and the PS8 (13%) conditions that returned to baseline after 10 min. Practical durations of stretching (2, 4, or 8 min) of the plantarflexors did not decrease isometric PT compared with the CON but caused temporary improvements in the ROM, thereby questioning the overall detrimental influence of PS on performance. Key Words: STRETCHING-INDUCED FORCE DEFICIT, EMG, MUSCLE ACTIVATION, RANGE OF MOTION