Relationship between changes in passive properties and muscle strength after static stretching.

Area of Science:

• Biomechanics
• Exercise Physiology
• Musculoskeletal Research

Background:

• The relationship between reduced muscle strength and rate of force development (RFD) post-static stretching (SS) and concurrent changes in muscle stiffness or slack remains poorly understood.
• Investigating these associations is crucial for understanding the physiological adaptations to stretching.

Purpose of the Study:

• To examine the correlation between changes in maximal voluntary contraction torque and RFD with alterations in muscle stiffness and muscle slack immediately following static stretching.
• To clarify the underlying mechanisms responsible for strength deficits after SS.

Main Methods:

• Sixteen healthy male volunteers underwent a 300-second static stretching intervention targeting the medial gastrocnemius muscle.
• Maximal voluntary contraction torque and shear elastic modulus (muscle stiffness) were measured before and after the stretching protocol.

Main Results:

• A significant decrease in maximal voluntary contraction torque and RFD was observed after 300 seconds of SS (p < 0.01).
• Muscle stiffness (shear elastic modulus at 0°) and muscle slack (slack angle) also significantly decreased post-stretching (p < 0.01).
• No significant association was found between the changes in muscle strength/RFD and the changes in muscle stiffness or slack.

Conclusions:

• The reduction in muscle strength and RFD following static stretching is not directly attributable to changes in the passive mechanical properties (stiffness and slack) of the medial gastrocnemius muscle.
• These findings suggest that neural factors or other unmeasured mechanisms may play a more significant role in the acute strength deficits observed after SS.