Lower Extremity Power Generation and Absorption during the Single- Leg Hop Test

Abstract

0716 The single-leg hop (SLH) for distance is a commonly used clinical test for patients with knee pathology (e.g. ACL injury). Typically, only the distance hopped is compared between injured and uninjured limbs. However, there is little information in the literature regarding the takeoff and landing biomechanics of this test; most published research focuses on the biomechanics of drop-landings. PURPOSE: The purpose of this study was to compare energy generation and absorption strategies in the lower extremity during the SLH test. METHODS: We recorded kinetic and kinematic data from five subjects as they performed the SLH test for distance. Motion data were collected at 60 Hz using six infrared cameras (Qtrac, Qualysis). Reflective markers were placed on bony landmarks according to a modified Helen Hayes configuration. Ground reaction forces were recorded at 1000 Hz with a force plate (Kistler). Using an inverse dynamic model, we calculated sagittal plane joint power at the ankle, knee and hip for each takeoff and landing. All joint powers were normalized to body mass. Paired t-tests were used to compare peak joint power during takeoff and landing at the ankle, knee and hip. P-values less than 0.05 were considered significant. RESULTS: For all joints, powers were positive during takeoffs, indicating energy generation and negative during landings, indicating energy absorption. Peak power at the ankle was significantly greater during takeoff than during landing (p = 0.002). At the knee, peak power was significantly greater during landing (p = 0.005). No significant difference in peak power was observed at the hip (p = 0.832). Additionally, peak power absorbed at the knee during landing was greater than that at the ankle (p < 0.001) and at the hip (p = 0.014). CONCLUSION: This study showed that greater demand is placed on the knee in landing compared to takeoff during the SLH. Also, the knee serves as the primary shock absorber of the lower extremity during landing. Consequently, analysis of the landing phase of the SLH should provide more information about knee performance than distance hopped.Table 1: Comparison of Joint Powers (W/kg) between Takeoff and Landing (SD)