Optimizing PNF stretching strategies for hamstring flexibility: Comparing end- and mid-range stretching effects by muscle tightness severity

Background When the hamstring muscles are tight, the risk of injury during physical activity increases, prompting the frequent use of active interventions, such as stretching, in clinical settings. However, most previous proprioceptive neuromuscular facilitation (PNF) stretching studies have been conducted at the end-range of motion, which does not correspond with the point of maximal force output according to the length–tension relationship. The purpose of this study was to compare the effects of PNF stretching performed at the mid-range, where optimal force production is theoretically possible, with those performed at the end-range. Additionally, it aimed to investigate whether flexibility gains differed according to the degree of hamstring tightness. Methods Hamstring tightness was evaluated using the active knee extension (AKE) test. Participants were categorized into severe and mild tightness groups. PNF stretching was performed at either 100% of maximal range of motion (MaxROM) or 50% MaxROM. Flexibility changes were assessed post-intervention using the AKE test. Results In the severe hamstring tightness group, significant flexibility improvements were observed after PNF stretching at both 100% and 50% MaxROM. In contrast, the mild hamstring tightness group showed significant improvement only at 100% MaxROM. Conclusions The effectiveness of PNF stretching in increasing flexibility varies according to joint position (100% vs. 50% MaxROM) and the initial severity of tightness. Notably, individuals with severe tightness experienced significant gains even at mid-range, suggesting that mid-range PNF stretching may serve as a viable alternative for patients who experience discomfort or pain at maximal ranges.