Drop Jump (DJ)

DJ assess the ability to redirect the body center of mass upwards after jumping from an elevated surface, providing a reliable measure known as the 'Reactive Strength Index' (RSI).

About:
Similar to the SJ, the DJ is a complimentary assessment to the CMJ for the ability to redirect the body center of mass vertically, this time after dropping from an elevated surface. Where the SJ minimizes involvement of the stretch shortening cycle, the DJ accentuates it. To perform the DJ, the athlete stands at the edge of an elevated surface (left panel in the figure above), typically a box of some kind (typically 12-24 inches, but this should be scaled to their individual capability), and proceeds to step off landing on both feet (middle panel in the figure above), decelerating quickly before rapidly accelerating in the opposite direction (right panel in the figure above). The intention of the athlete should be to jump as high as possible. Individuals may differ in landing depth: some may land closer to a half squat while others may remain more stiff legged only lower to a quarter squat before re-accelerating upwards.

The DJ is a reliable clinical assessment for ACL injury risk, but also provides a powerful method for training athlete's stretch shortening cycle. Reactive Strength Index (RSI), a relative measure of ground contact time and jump height, reflects neuromuscular fatigue making the DJ a useful tool to indicate readiness to train.

References:
[1] Bobbert, M. F., Mackay, M., Schinkelshoek, D., Huijing, P. A., & Van Ingen Schenau, G. J. (1986). Biomechanical analysis of drop and countermovement jumps. European Journal of Applied Physiology and Occupational Physiology, 54(6), 566–573. https://doi.org/10.1007/BF00943342
[2] Flanagan, E. P., & Comyns, T. M. (2008). The Use of Contact Time and the Reactive Strength Index to Optimize Fast Stretch-Shortening Cycle Training. Strength & Conditioning Journal, 30(5), 32–38. https://doi.org/10.1519/SSC.0b013e318187e25b
[3] Pedley, J. S., Lloyd, R. S., Read, P., Moore, I. S., & Oliver, J. L. (2017). Drop Jump: A Technical Model for Scientific Application. Strength & Conditioning Journal, 39(5), 36–44. https://doi.org/10.1519/SSC.0000000000000331
[4] Redler, L. H., Watling, J. P., Dennis, E. R., Swart, E., & Ahmad, C. S. (2016). Reliability of a field-based drop vertical jump screening test for ACL injury risk assessment. The Physician and Sportsmedicine, 44(1), 46–52. https://doi.org/10.1080/00913847.2016.1131107