title: Lower hamstring extensibility in men compared to women is explained by differences in stretch tolerance.
abstract: BACKGROUND
  This study examined whether passive hamstring tissue stiffness and/or stretch tolerance explain the relationship between sex and hamstring extensibility.
  
  
  METHODS
  Ninety healthy participants, 45 men and 45 women (mean ± SD; age 24.6 ± 5.9 years, height 1.72 ± 0.09 m, weight 74.6 ± 14.1 kg) volunteered for this study. The instrumented straight leg raise was used to determine hamstring extensibility and allow measurement of stiffness and stretch tolerance (visual analog pain score, VAS).
  
  
  RESULTS
  Hamstring extensibility was 9.9° greater in women compared to men (p = 0.003). VAS scores were 16 mm lower in women (p = 0.001). Maximal stiffness (maximal applied torque) was not different between men and women (p = 0.42). Passive stiffness (slope from 20-50° hip flexion) was 0.09 Nm.°(-1) lower in women (p = 0.025). For women, linear and stepwise regression showed that no predictor variables were associated with hamstring extensibility (adjusted r(2) = -0.03, p = 0.61). For men, 44% of the variance in hamstring extensibility was explained by VAS and maximal applied torque (adjusted r(2) = 0.44, p < 0.001), with 41% of the model accounted for by the relationship between higher VAS scores and lower extensibility (standardized β coefficient = -0.64, p < 0.001).
  
  
  CONCLUSIONS
  The results of this study suggest that stretch tolerance and not passive stiffness explains hamstring extensibility, but this relationship is only manifest in men.
authors.affiliation: School of Science and Health, University of Western Sydney, Locked Bag 1797, Penrith South, NSW 2751, Australia. p.marshall@uws.edu.au.
authors.forename: Paul W M
authors.initials: PW
authors.lastname: Marshall
authors.forename: Jason C
authors.initials: JC
authors.lastname: Siegler
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004548:Elasticity; D005260:Female; D006801:Humans; D035002:Lower Extremity; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D010147:Pain Measurement; D017288:Pain Threshold; D012737:Sex Factors; D055815:Young Adult