PURPOSE: Hormonal fluctuations are one potential reason why females might have a greater rate of noncontact @entity130 . The hamstrings are capable of limiting anterior cruciate ligament (ACL) loading. This study examined whether relationships existed between reproductive hormones ( @entity53 -b-17, free @entity251 , and @entity1420 ) and hamstring neuromechanical variables (hamstring @entity2693 ( @entity2693 ), @entity1168 ( @entity1168 ), time to 50% peak torque (T50%), and @entity245 ( @entity245 )) in genders combined and independently. METHODS: Muscle properties of the hamstrings and reproductive hormones were evaluated in 30 subjects (15 males and 15 females) that were free from @entity130 and had no history of @entity130 . Females were tested 3-5  days after the onset of menses and were not using oral contraceptive. Pearson correlation coefficients were calculated for each hormone and muscle property. RESULTS: For genders combined, @entity172 (mean  =  46.0      28.2  pg/mL) was negatively correlated with @entity1168 (mean  =  758.8      507.6  N/kg  s(-1), r  =  -0.43, P  =  0.02) and @entity2693 (mean  =  12.8      2.6  N/cm, r  =  -0.43, P  =  0.02). Free @entity251 (mean  =  13.2      13.0  pg/mL) was positively correlated with @entity1168 (r  =  0.56, P  <  0.01) and @entity2693 (r  =  0.46, P  =  0.01) but negatively correlated with T50% (mean  =  114.7      38.9  ms, r  =  -0.43, P  =  0.02). When gender was considered separately, females demonstrated negative correlation between @entity172 (mean  =  68.0      23.2  pg/mL) and @entity2693 (mean  =  11.7      1.5  N/cm, r  =  -0.53, P  =  0.05) and free @entity251 (mean  =  1.5      0.6  pg/mL) and @entity2693 (r  =  -0.52, P  =  0.05). Males alone displayed no significant correlations between the selected hormones and muscle properties. CONCLUSIONS: Correlations exist between muscle properties and reproductive hormones. Females, however, may be more sensitive to reproductive hormones and their fluctuations.

XXXX and muscle stiffness have a negative relationship in females.

@entity172 :: ('MESH:D004967', 'Chemical') :: ['estrogen'] @entity251 :: ('MESH:D013739', 'Chemical') :: ['testosterone'] @entity1420 :: ('MESH:D011374', 'Chemical') :: ['progesterone'] @entity245 :: ('MESH:D002658', 'Disease') :: ['EMD', 'electromechanical delay'] @entity53 :: ('MESH:D004958', 'Chemical') :: ['estradiol'] @entity1168 :: ('MESH:D001919', 'Disease') :: ['RFP', 'rate of force production'] @entity130 :: ('MESH:D014947', 'Disease') :: ['lower extremity injury', 'ACL injury'] @entity2693 :: ('MESH:C566112', 'Disease') :: ['musculotendinous stiffness', 'MTS']
@entity172 :: (MESH:D004967,Chemical) :: ['Estrogen']
