Effect of 12-week dynamic stretching of hamstrings on joint flexibility and musculoskeletal properties

This study aimed to examine the effects of a 12‑week hamstrings dynamic stretching (DS) program on joint flexibility, muscle strength, and musculoskeletal properties in the stretched limb, with the non‑stretched limb assessed for comparison.

The study comprised 18 healthy young adults (12 males, 6 females) who performed hamstrings DS on one leg three times per week for 12 weeks, with the contralateral leg serving as the control. Pre- and post-intervention assessments included knee extension range of motion (KEROM), peak passive torque during KEROM (stretch tolerance), muscle stiffness, and knee flexor strength. Muscle stiffness was evaluated using shear-wave elastography targeting the biceps femoris (BF). Knee flexor strength was assessed using the rate of torque development (RTD) and isokinetic knee flexion torque.

KEROM significantly increased in the DS condition (p = 0.025; d = 0.61), with no significant change in the control condition (p = 0.55; d = 0.15). Peak passive torque significantly increased following DS (p = 0.041; d = 0.68), with no change in the contralateral limb (p = 0.21; d = 0.21). BF stiffness significantly decreased in the DS condition and remained unchanged in the contralateral limb (70° knee flexion: DS, p < 0.01, d = 0.79; control, p = 0.30, d = 0.30; 50° knee flexion: DS, p = 0.044, d = 0.55; control, p = 0.18, d = 0.34. RTD and isokinetic knee flexion strength did not change significantly in either condition.

Twelve weeks of hamstrings DS enhanced stretch tolerance, reduced muscle stiffness, and improved joint flexibility in the stretched limb, with no notable changes observed in the contralateral limb.

Name of trial registry Effects of training and conditioning methods on mechanical properties of skeletal muscle Identifying number (URL) UMIN000051819 ( https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000058080 ) Date of registration 5th Aug 2023.