Hamstrings passive and active shear modulus: Implications of conventional static stretching and warmup

Area of Science:

• Biomechanics and Exercise Physiology
• Muscle Physiology

Background:

• Understanding the acute effects of different physical interventions on muscle mechanical properties is crucial for optimizing athletic performance and injury prevention.
• The hamstring muscle group comprises multiple muscles with potentially distinct responses to interventions like stretching and warming up.

Purpose of the Study:

• To compare the acute effects of static stretching versus a standard warmup protocol on the active and passive shear modulus of individual hamstring muscles.
• To investigate muscle-specific responses within the hamstring group to these interventions.

Main Methods:

• Muscle shear modulus was measured at rest and during submaximal isometric contractions (20% of maximal voluntary isometric contraction - MVIC).
• Measurements were taken before and after static stretching and a standard warmup protocol.
• Key hamstring muscles, including the biceps femoris short head (BFsh) and semimembranosus (SM), were analyzed.

Main Results:

• Static stretching altered the passive shear modulus pattern inconsistently across muscles and significantly changed the active shear modulus during contraction, leading to differences between BFsh and SM.
• Static stretching was associated with an 18.3% decrease in MVIC.
• A standard warmup protocol did not significantly alter passive shear modulus, and while it showed a small decrease in the active shear modulus of the semitendinosus, this was within the measurement error and did not impact force production (1.4% increase).

Conclusions:

• The acute effects of static stretching on passive and active hamstring shear modulus are muscle-specific.
• A standard warmup protocol appears to have a negligible effect on passive and active hamstring shear modulus and does not impair force production.