Fascial and muscle ultrasound parameters unchanged after stretching or eccentric training in young men with hamstring tightness

Introduction

Hamstring tightness has been associated with significant mobility impairments and potential health issues. However, the effects of long-duration stretching (LS) on structural adaptations and joint extensibility remain unclear and underexplored. This study aimed to investigate the effects of stretching on fascia thickness (FT), muscle ultrasound characteristics, and leg flexibility in young men with hamstring inflexibility.

Methods

Sixty-eight physically active young men (22.0 ± 1.7 years) were randomly assigned to one of four groups: LS (60s × 60), standard stretching (SS; 30s × 6), eccentric exercise (ECC), or control (CON). FT, muscle ultrasound characteristics, and leg flexibility—assessed via the straight leg raise (SLR) and knee-to-wall (KTW) tests—were measured before and after a 6-week intervention period.

Results

Significant increases in SLR were observed following the intervention, with improvements of 9.8° (d = 1.53), 5.7° (d = 0.96), 5.5° (d = 1.10), and 3.5° (d = 0.60) for the LS, SS, ECC, and CON groups, respectively (all p < 0.05). A significant main effect of time, in the absence of a time-by-group interaction, was found for KTW, fascicle length of the biceps femoris (BF), and subcutaneous thickness of both the BF and medial gastrocnemius muscles. Conversely, no significant changes were detected in FT or echo intensity as a result of the intervention.

Conclusion

LS did not produce superior improvements in flexibility, fascicle length, or FT compared to SS or ECC after six weeks. A 5-min SS session is recommended as an effective, time-efficient approach for improving range of motion in individuals with mild hamstring tightness.