Lower hamstring extensibility in men compared to women is explained by differences in stretch tolerance.

Area of Science:

• Biomechanics
• Human Physiology
• Kinesiology

Background:

• Investigating sex-based differences in hamstring extensibility.
• Examining the roles of passive tissue stiffness and stretch tolerance.

Purpose of the Study:

• Determine if passive hamstring tissue stiffness or stretch tolerance explains sex differences in hamstring extensibility.
• Clarify the relationship between sex, stiffness, stretch tolerance, and hamstring flexibility.

Main Methods:

• Utilized the instrumented straight leg raise technique on 90 healthy participants (45 men, 45 women).
• Measured hamstring extensibility, passive stiffness, and stretch tolerance (visual analog pain score - VAS).

Main Results:

• Women exhibited significantly greater hamstring extensibility (9.9°) and lower VAS scores compared to men.
• No significant difference in maximal stiffness between sexes.
• Passive stiffness was lower in women.
• In men, VAS and maximal applied torque explained 44% of hamstring extensibility variance, with higher VAS linked to lower extensibility.

Conclusions:

• Stretch tolerance, not passive stiffness, appears to be the primary factor influencing hamstring extensibility.
• This relationship between stretch tolerance and hamstring extensibility is evident only in men.
• Findings suggest sex-specific mechanisms underlying hamstring flexibility.