Differences In Mechanics Between First And Second Drop Vertical Jump Landings

Abstract

PURPOSE: A drop jump and landing, followed by another maximal jump and landing, has been used when assessing injury risk using the Landing Error Scoring System (LESS). The LESS provides a way to measure frontal and sagittal plane alignment during landing and has traditionally used the first, but not the second, landing for assessment. Additionally, vertical ground reaction force (vGRF) and knee excursion are commonly analyzed during a drop vertical jump. The purpose of this study was to investigate whether there was a difference in LESS scores, vGRF, and knee excursion between the first and second landings of the drop vertical jump. METHODS: Forty healthy subjects performed a drop vertical jump from a 30 cm box with an initial landing (L1) immediately followed by a second maximal jump and landing (L2). Three trials were scored using the LESS. Subjects were dichotomized as “high risk” on the LESS if they had a score greater than 5 (including moderate and poor scores) and “low risk” (including good and excellent scores) if they scored 5 or under. Jump height, peak vGRF, and knee excursion were recorded using an in-ground force plate and a 3-D motion analysis system. To further analyze the data, subjects were separated into “high” and “low” jumpers by dichotomizing the average jump height. Statistical analysis was performed with SPSS (version 25.0) to identify whether there were significant differences in LESS scores, peak vGRF, and knee excursion between landings for all subjects and “high” and “low” jumpers. RESULTS:CONCLUSIONS: The significant increase in LESS scores and peak vGRF between landings suggests that the second landing may be more indicative of injury risk when using the LESS. Low height jumpers had greater injury risk due to significantly higher LESS scores and minimal changes in knee excursion from landing one to landing two.