Stretching of Active Muscle Elicits Chronic Changes in Multiple Strain Risk Factors.

Area of Science:

• Exercise Physiology
• Biomechanics
• Sports Medicine

Background:

• Muscle stretch intensity impacts joint range of motion (ROM) adaptation.
• Active muscle stretching may offer greater stimulus than passive stretching.
• Understanding muscle-tendon mechanics during active stretching is crucial for injury prevention and performance enhancement.

Purpose of the Study:

• To investigate the effects of a 6-week active stretching program on muscle-tendon mechanics.
• To compare adaptations from stretching an isometrically contracting muscle versus passive stretching.
• To analyze changes in joint ROM, passive moment, muscle and tendon stiffness, and maximal voluntary contraction.

Main Methods:

• 13 healthy volunteers underwent a 6-week training program involving maximal isokinetic eccentric contractions.
• Measurements included dorsiflexion ROM, passive joint moment, and maximal isometric plantarflexor moment.
• Real-time motion analysis and ultrasound imaging tracked muscle and tendon elongation during training.

Main Results:

• Significant increases observed in ROM (92.7%), peak passive moment (136.2%), energy storage (302.6%), and maximal isometric plantarflexor moment (51.3%).
• Tendon stiffness increased significantly (31.2%), while passive muscle stiffness decreased (-14.6%).
• No significant change in overall muscle-tendon stiffness was detected.

Conclusions:

• Stretching active muscle leads to substantial improvements in functional and physiological variables, including strength, ROM, and energy storage.
• Tissue-specific adaptations occurred, with increased tendon stiffness and decreased passive muscle stiffness.
• Active muscle stretching may positively influence muscle function and potentially reduce the risk of muscle strain injuries.