Acute and Chronic Effects of Static Stretching on Intramuscular Hamstring Stiffness

Area of Science:

• Biomechanics
• Sports Medicine
• Muscle Physiology

Background:

• Passive hamstring stiffness is not uniform along the muscle length.
• Inhomogeneous strain during stretching may influence muscle adaptation and injury risk.

Purpose of the Study:

• To investigate the acute and chronic effects of static stretching (SS) on intramuscular hamstring stiffness.
• To examine regional differences in stiffness changes within the hamstring muscles.

Main Methods:

• Shear-wave elastography was used to measure passive biceps femoris (BF), semimembranosus (SM), and semitendinosus (ST) stiffness at proximal, middle, and distal regions.
• Acute effects of SS were measured immediately post-stretching.
• Chronic effects were assessed after a 4-week SS intervention (n=15) compared to a control group (CON, n=15).

Main Results:

• Acutely, SS reduced stiffness in BF and SM, with greater reductions in stiffer regions of SM and ST.
• Chronically, SS increased stiffness in BF and ST compared to CON, but not in SM.
• No regional effects on stiffness were observed after the chronic intervention.

Conclusions:

• Static stretching has contrasting acute and chronic effects on hamstring stiffness.
• Acutely, SS decreases stiffness, particularly in stiffer muscle regions.
• Chronic SS leads to increased stiffness in specific hamstring muscles, independent of initial regional stiffness variations.