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The aim of this study was to investigate the relationship between the kinematics and kinetics of a singleleg horizontal drop jump (SLDJ) to sprint performance. Twenty regional-level male team-sport athletes gave informed consent to participate in this study. All subjects performed a series of 25-m sprints (measured by dual-beam infrared timing lights) and SLDJ (with both legs) in randomized block order during the same testing session. The SLDJ required the subjects to step downwards off a 20-cm box, land on the force plate (operating at 500 Hz) with the specified foot, and jump for maximal horizontal distance while minimizing ground-contact time. Jump distance, particularly when normalized to a subject's height, was the strongest correlate to sprinting time for all three (5, 10, and 25 m) distances (-0.44 < r < -0.65). Multiple linear regression analyses indicated that the SLDJ could account for a high level of variance in sprint time (0.49 < [r.sup.2] < 0.68) and that these predictions had a relatively low standard error of estimate (0.020.10 seconds). These results further support the contention that jump (particularly horizontal) and sprint ability for short distances are highly related. Whereas practitioners should consider using more horizontal than vertical jumps in the training and testing of most team-sport athletes, additional, research into the kinetic determinants of jumping and sprinting may allow a more specific and individualized exercise prescription for improving certain aspects of sprinting such as step length or step rate or the vertical vs. horizontal contributions to propulsion.

Determining the reliability of a unilateral horizontal drop jump for displacement provided the focus for this research. Eighteen male subjects were required to step off a 20cm box and land on a force plate with one leg and thereafter jump for maximal horizontal displacement on two different days. Dependent variables from the jump assessment included mean and peak vertical (V) and horizontal (H) ground reaction forces (GRF) and impulses, horizontal displacement and contact time. The between-trial variability of all kinematic and kinetic measures was less than 7%. The most consistent measure over both trials was the horizontal displacement jumped (1.2 to 1.4%) and the most variable were the contact time the first day (6.5%) and peak HGRF the second day (4.3%). In all cases there was less variation associated with the second rather than the first day. In terms of test-retest variability the percent changes in the means and coefficient of variations (CVs) were all under 10%. The smallest changes in the mean (0.43 %), least variation (< 2.26 %) and second highest intraclass correlation co-efficient (ICC = 0.95) were found for horizontal displacement jumped. The highest ICC (0.96) was found for horizontal impulse. Given the reliability of the single leg drop jump, it may offer better prognostic and diagnostic information than that obtained with bilateral vertical jumps. Key pointsThere is a need for greater understanding and utilisation of assessment techniques that assess both the horizontal and vertical components of force/power production.The single leg drop jump is an assessment that exhibits high face validity (a unilateral jump involving both vertical and horizontal propulsive forces that also involves pre-load) but reliability needed to be quantified.The reliability of the many kinematic and kinetic variables quantified in this study were similar to those published in research in this area and future research needs to determine the clinical and practical significance of this test.