Static stretching at pain-tolerated intensity is not necessary to increase knee range of motion in amateur soccer players: A randomized trial

Abstract

Background. Stretching exercises are commonly used in warm-up routines before sports practice. However, there is a lack of evidence regarding the optimal intensity at which passive stretching should be performed in soccer players. This study investigated the acute and chronic effects of different static stretching intensities on the knee ROM, passive torque and functional performance of amateur soccer players. Methods. Forty-one male amateur soccer players were allocated into four groups: no stretching (NS, n = 10), comfort level stretching (CLS, n = 11), mild discomfort level stretching (MDLS, n = 10) or pain level stretching (PLS, n = 10). Three 30-second sessions of static passive hamstring muscle stretching were performed 3 times a week, totaling 10 sessions. Intensities were established according to the scale of perceived effort in flexibility. Passive and active knee extension ROM, passive peak torque (PPT), PPT angulation, viscoelastic stress-relaxation and modified shuttle run were measured at baseline, post 1st session (acute effect), and 48 h after the 10th session (chronic effect). Discomfort/pain and affective responses were recorded after each session and at the end of training, respectively. Results. No intergroup differences were observed after the 1st session. However, 48 h after the 10th session, the MDLS and PLS groups exhibited a similar significant increase in active and passive knee extension ROM compared to the NS (P < 0.01, effect size = 1.8 to 2.6) and CLS (P < 0.01, effect size = 1.5 to 2.4). There were no inter-group differences for the other outcomes. Conclusions. Static stretching exercises do not need to be prescribed at pain-tolerated intensity for knee flexibility gains in amateur soccer players.