Viscoelastic response to repeated static stretching in the human hamstring muscle

Area of Science:

• Biomechanics
• Human Physiology
• Musculoskeletal Research

Background:

• Understanding passive resistance to stretch is crucial for injury prevention and rehabilitation.
• Previous methods for measuring muscle resistance have limitations in reproducibility and in vivo application.
• The hamstring muscle group is frequently implicated in sports injuries, necessitating accurate measurement techniques.

Purpose of the Study:

• To validate a novel in vivo method for assessing passive resistance in the human hamstring muscle group.
• To investigate the reproducibility of this measurement technique using a test-retest protocol.
• To analyze the impact of repeated static stretching on hamstring passive resistance and its viscoelastic properties.

Main Methods:

• Ten healthy subjects participated in the study.
• Passive resistance was measured as knee flexion moment (Nm) using a KinCom dynamometer during passive knee extension at 5 deg/s.
• Electromyography (EMG) of the hamstring muscles was recorded concurrently with resistance measurements during static holds and repeated stretches.

Main Results:

• The novel method demonstrated high test-retest reproducibility for hamstring passive resistance.
• Passive resistance showed a time-dependent decline within each stretch, indicating viscoelastic behavior.
• Repeated stretching (5 consecutive bouts) significantly reduced passive resistance, with a diminished decline over time and a lasting effect observed 1 hour later.

Conclusions:

• A reliable and reproducible in vivo method for measuring hamstring passive resistance has been established.
• The human hamstring muscle exhibits viscoelastic properties, with resistance decreasing over time and with repeated stretches.
• Repeated stretching protocols can effectively reduce hamstring passive resistance, suggesting implications for flexibility and injury management.