The effects of different passive static stretching intensities on recovery from unaccustomed eccentric exercise – a randomized controlled trial

Effects of passive static stretching intensity on recovery from unaccustomed eccentric exercise of right knee extensors was investigated in 30 recreationally active males randomly allocated into 3 groups: high-intensity (70%–80% maximum perceived stretch), low-intensity (30%–40% maximum perceived stretch), and control. Both stretching groups performed 3 sets of passive static stretching exercises of 60 s each for hamstrings, hip flexors, and quadriceps, over 3 consecutive days, post-unaccustomed eccentric exercise. Muscle function (eccentric and isometric peak torque) and blood biomarkers (creatine kinase and C-reactive protein) were measured before (baseline) and after (24, 48, and 72 h) unaccustomed eccentric exercise. Perceived muscle soreness scores were collected immediately (time 0), and after 24, 48, and 72 h postexercise. Statistical time × condition interactions observed only for eccentric peak torque (p = 0.008). Magnitude-based inference analyses revealed low-intensity stretching had most likely, very likely, or likely beneficial effects on perceived muscle soreness (48–72 h and 0–72 h) and eccentric peak torque (baseline–24 h and baseline–72 h), compared with high-intensity stretching. Compared with control, low-intensity stretching had very likely or likely beneficial effects on perceived muscle soreness (0–24 h and 0–72 h), eccentric peak torque (baseline–48 h and baseline–72 h), and isometric peak torque (baseline–72 h). High-intensity stretching had likely beneficial effects on eccentric peak torque (baseline–48 h), but likely had harmful effects on eccentric peak torque (baseline–24 h) and creatine kinase (baseline–48 h and baseline–72 h), compared with control. Therefore, low-intensity stretching is likely to result in small-to-moderate beneficial effects on perceived muscle soreness and recovery of muscle function post-unaccustomed eccentric exercise, but not markers of muscle damage and inflammation, compared with high-intensity or no stretching.