Acute Effects of the Different Intensity of Static Stretching on Flexibility and Isometric Muscle Force

<jats:title>Abstract</jats:title> <jats:p>Kataura, S, Suzuki, S, Matsuo, S, Hatano, G, Iwata, M, Yokoi, K, Tsuchida, W, Banno, Y, and Asai, Y. Acute effects of the different intensity of static stretching on flexibility and isometric muscle force. <jats:italic toggle="yes">J Strength Cond Res</jats:italic> 31(12): 3403–3410, 2017—In various fields, static stretching is commonly performed to improve flexibility, whereas the acute effects of different stretch intensities are unclear. Therefore, we investigated the acute effects of different stretch intensities on flexibility and muscle force. Eighteen healthy participants (9 men and 9 women) performed 180-second static stretches of the right hamstrings at 80, 100, and 120% of maximum tolerable intensity without stretching pain, in random order. The following outcomes were assessed as markers of lower limb function and flexibility: static passive torque (SPT), range of motion (ROM), passive joint (muscle-tendon) stiffness, passive torque (PT) at onset of pain, and isometric muscle force. Static passive torque was significantly decreased after all stretching intensities (<jats:italic toggle="yes">p</jats:italic> ≤ 0.05). Compared with before stretching at 100 and 120% intensities, ROM and PT were significantly increased after stretching (<jats:italic toggle="yes">p</jats:italic> ≤ 0.05), and passive stiffness (<jats:italic toggle="yes">p</jats:italic> = 0.05) and isometric muscle force (<jats:italic toggle="yes">p</jats:italic> ≤ 0.05) were significantly decreased. In addition, ROM was significantly greater after stretching at 100 and 120% than at 80%, and passive stiffness was significantly lower after 120% than after 80% (<jats:italic toggle="yes">p</jats:italic> ≤ 0.05). However, all measurements except SPT were unchanged after 80% intensity. There was a weak positive correlation between the intensities of stretching and the relative change for SPT (<jats:italic toggle="yes">p</jats:italic> ≤ 0.05), a moderate positive correlation with ROM (<jats:italic toggle="yes">p</jats:italic> ≤ 0.05), and a moderate positive correlation with passive stiffness (<jats:italic toggle="yes">p</jats:italic> ≤ 0.05). These results indicate that static stretching at greater intensity is more effective for increasing ROM and decreasing passive muscle-tendon stiffness.</jats:p>