A Hop Testing Alternative For Lower Extremity Power Following Anterior Cruciate Ligament Reconstruction

Isokinetic testing is a valuable return to sport (RTS) tool after anterior cruciate ligament reconstruction (ACLR); but it requires specialized equipment. Hop testing is widely used for RTS, but metrics like time and distance do not expose underlying biomechanical deficits. PURPOSE: This study aimed to provide a measure of lower extremity power in the 6-meter timed hop test (6mTH). We hypothesized that reactive strength ratio (RSR) during hop testing would be lower in involved limbs of our low isokinetic power symmetry group (low-IPS) as compared to their uninvolved limbs and involved limbs of a high isokinetic power symmetry group (high-IPS). METHODS: 23 ACLR patients (M/F: 13/10; Age: 26.35 ± 9.18 y; Time Since Surgery: 40.9 ± 13.5 weeks) completed isokinetic and hop testing at > 6 months after surgery. Isokinetic testing was conducted at 60, 180, and 300 deg·s-1. The 6mTH was administered while 35 reflective markers were tracked by a 10-camera motion capture system. RSR, the ratio of flight time to ground contact time, was calculated using events determined from the pelvis linear velocity norm. Given the similarity to knee joint velocities encountered in the 6mTH, the patients were dichotomized into groups using isokinetic power symmetry at 300 deg·s-1 with a cutoff of 85%. A mixed repeated measures ANOVA (leg x group) with LSD post hoc testing was used to determine significant main effects or interactions for RSR and relative isokinetic average power (rAP) at 300 deg·s-1. RESULTS: A significant interaction was found for RSR (F[1,21]: 10.59, p < .01, η2 = .334, Observed power = .87) and rAP (F[1,21]: 24.19, p < .001, η2 = .54, Observed power = .99). Post hoc comparisons showed lower RSR (MD±SE: -.19 ± .05, p < .001, Cohen’s d = -.84) and rAP (MD±SE: -1.01 ± .15 W·kg-1, p < .001, Cohen’s d = -1.09) in the involved limbs compared to uninvolved limbs for low-IPS. The involved limbs of low-IPS also showed lower RSR (MD±SE: -.26 ± .09, p < .01, Cohen’s d = -1.25) and rAP (MD±SE: -1.08 ± .38 W·kg-1, p < .05, Cohen’s d = -1.19) compared to the high-IPS involved limbs. CONCLUSION: Low-IPS showed greater deficits in rAP, which was consistent with lower RSR in the involved limbs whereas no interlimb differences were found in high-IPS cohorts. RSR may be an alternative to quantify power for ACLR RTS testing in the absence of isokinetic dynamometry.