European journal of applied physiology 2017 06 24() doi 10.1007/s00421-017-3666-1
The purpose of this study was to compare the benefits and possible problems of 4 weeks stretching when taken to the point of pain (POP) and to the point of discomfort (POD).
Twenty-six physically active women (20 ± 1.1 years) took part in group-based stretching classes of the hamstring muscles, 4 times per week for 4 weeks, one group one stretching to POD, the other to POP. Passive stiffness, joint range of motion (ROM), maximal isometric torque and concentric knee flexion torque, were measured before training and 2 days after the last training session.
Hip flexion ROM increased by 14.1° (10.1°-18.1°) and 19.8° (15.1°-24.5°) and sit-and-reach by 7.6 (5.2-10.0) cm and 7.5 (5.0-10.0) cm for POD and POP, respectively (Mean and 95% CI; p < 0.001 within group; NS between groups), with no evidence of damage in either group. Despite the large increases in flexibility there were no changes in either compliance or viscoelastic properties of the muscle tendon unit (MTU). CONCLUSION
Hamstrings stretching to POP increased flexibility and had no detrimental effects on muscle function but the benefits were no better than when stretching to POD so there is no justification for recommending painful stretching. The improvements in flexibility over 4 weeks of stretching training appear to be largely due to changes in the perception of pain rather than physical properties of the MTU although less flexible individuals benefited more from the training and increased hamstring muscle length.