LIMB SYMMETRY IS NOT ENOUGH: ESTABLISHMENT OF HEIGHT NORMALIZED HOP DISTANCES WITHIN HEALTHY YOUTH ATHLETES

BACKGROUND: Most experts recommend utilizing single leg hop tests to help determine an athlete’s readiness to return to sports after anterior cruciate ligament reconstruction (ACLR). A limb symmetry index (LSI =involved limb/uninvolved limb) of ≥90% is typically required by most contemporary protocols. However, limb symmetry may underestimate continued post-operative deficits due to performance declines within the uninvolved limb after ACLR. Additionally, LSI may not accurately identify those at risk of repeat injury, and doesn’t assist in ensuring maximal patient effort. Comparing height normalized hop distances to uninjured controls has been suggested as an additional criteria to better recognize performance deficits after ACLR. PURPOSE: To characterize single leg hop test performance in a large group of healthy youth athletes and determine the relationships of sex or age on hop performance. METHODS: This was a cross-sectional study of healthy youth athletes aged 8-14 years-old, who were currently participating in organized sports. Using their dominant leg, each subject performed a triple hop (TrH) in which they quickly hopped on one leg three times, achieving maximal linear distance, while holding their balance after the last hop. Distance from starting line to the heel was recorded in centimeters. Each subject’s hop distance was normalized to body height and served as the dependent variable. A two-way ANOVA analyzed any effects of age and sex. A-priori alpha was set at p≤0.05. RESULTS: A total of 340 subjects (Male [n=184], mean age 10.9±1.5 years) were included. Across the entire sample, mean TrH distance was 2.2 times body height. ANOVA demonstrated no differences for main effect of sex (mean TrH/height, Males=2.2, Females=2.1, p=0.212). (Figure 1) Main effect of age was significant (p<0.001) with Bonferroni post-hoc analysis indicating 13 year-olds normalized TrH distance (2.6 times body height) was greater than all other age groups (8 yrs=1.9, 9yrs=2.0, 10yrs=2.1, 11yrs=2.2, 12yrs=2.3). (Figure 2) The 12 year-old performance was significantly greater than 8-9 year-olds only (2.3 vs 1.9-2.0). CONCLUSIONS: When normalized to body height, TrH performance increases around the ages of 12-13 years. Regardless of sex, athletes aged 8-11 can be expected to TrH approximately 2 times body height, while athletes near age 13 should have TrH values of 2.6 times body height. Due to post-operative deconditioning within the healthy limb, the use of age-matched hopping norms in addition to LSI may offer better determination of functional recovery or effort. As performance changes with age, future research should focus on establishing normative performance in older subjects. Figures/Tables: