Sex differences in hamstrings (H) to quadriceps (Q) maximum voluntary force ratio have been proposed as a factor for increased ACL injury risk in females. It has been suggested that the lower ratio in females may in part be due to a smaller H muscle size relative to Q muscle size. However, this has not been thoroughly investigated.
PURPOSE: To investigate sex differences in H/Q muscle volume ratio.
METHODS: Following ethical approval, muscle volume of the H and Q muscles were determined from the dominant leg of 66 untrained participants (32 males mean ± SD: age, 20.6 ± 2.5 y; height, 178.8 ± 7.0 cm; mass, 71.8 ± 7.2 kg; and 34 females: age, 20.9 ± 1.7 y; height, 168.3 ± 0.1 cm; mass, 62.9 ± 7.2 kg). T1 weighted axial plane images were acquired from the anterior superior iliac spine to the knee joint space using a 1.5 T Magnetic Resonance Imaging scanner (Signa HDxt, GE, CT, USA) and processed with Osirix software (version 4.0, Pixmeo, Geneva, Switzerland). The ratio of H/Q muscle volume was determined. Sex differences were measured using independent samples t-tests.
RESULTS: Males had 53% greater H muscle volume (940.5 ± 125.6 cm3 vs 616.6 ± 127.7 cm3, P < 0.001) and 43% greater Q muscle volume (1940.9 ± 263.7 cm3 vs 1354.8 ± 254.2 cm3, P < 0.001), compared to females. H/Q values for males and females were 0.49 ± 0.05, and 0.46 ± 0.07 respectively, showing a significantly higher ratio in males compared to females (P < 0.05, Cohen’s D = 0.57).
CONCLUSION: In agreement with our hypothesis the H/Q ratio displayed a significantly higher value in males with a moderate effect size. Sex differences in H/Q muscle volume may contribute to the increased ACL injury risk in females. Further investigations of neuromuscular factors including muscle morphology further explaining this increased ACL risk in females are warranted.
Research funded by the Arthritis Research UK Centre for Sport, Exercise and Osteoarthritis.