Effect of gender and maturity on quadriceps-to-hamstring strength ratio and anterior cruciate ligament laxity

Background: Exercise programs have been introduced to reduce the ACL injury risk in female athletes. The most effective age at which to start these programs is not known. Hypothesis: Age and gender affect ligament laxity and quadriceps-to-hamstring strength ratio. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Fifty-three female and 70 male recreational soccer players, 10 to 18 years of age, were studied with physical examination, KT-1000 arthrometry, and manual maximum quadriceps and hamstring strength using a handheld dynamometer. The subjects were separated into 4 groups to examine maturity-related intergender differences: group G1, premenarchal girls (n = 24); group B1, boys 13 years and younger (n 38); group G2, girls 2 or more years after menarche (n = 29); and group B2, boys 14 years and older (n = 32). Results: Both knees of 123 soccer players were evaluated. The mean ages for groups G1, B1, G2, and B2 were 11.60 +/- 1.69, 10.63 +/- 1.85, 15.5 +/- 1.43, and 15.59 +/- 1.24 years, respectively, and the mean laxity measurements were 8.84 +/- 2.12, 8.51 +/- 1.61, 8.85 +/- 1.86, and 7.33 +/- 1.27 mm, respectively. Laxity was significantly less for the mature boys (P = .0015) than for the immature boys, mature girls, and immature girls. With increasing maturity, significant increases in both quadriceps and hamstring muscle strength were observed for both boys and girls (P < .05). Boys demonstrated a greater percentage increase in hamstring strength with maturity (179%) compared with girls (27%) (P < .05). Mature girls (2.06) had significantly greater quadriceps-to-hamstring ratio when compared with immature girls (1.74), immature boys (1.58), and mature boys (1.48) (P < .05). Conclusion: Female athletes after menarche increase their quadriceps strength greater than their hamstring strength, putting them at risk for anterior cruciate ligament injury. Anterior cruciate ligament-prevention programs based on improving dynamic control of the knee by emphasizing hamstring strengthening should be instituted for girls after menarche.