NCT07475078

Reactive Strength and Dynamic Rebound: A Drop Jump Index Comparison

Which Index Tells the Full Story? Comparing Reactive Strength and Dynamic Rebound Index in Drop Jump Performance

• Status: Not Yet Recruiting
• Phase: N/A
• Study type: Interventional
• Enrollment: 50 (estimated)
• Sponsor: University Institute of Maia · Academic / Other
• Sex: All
• Age: 18 Years
• Healthy volunteers: Accepted

Summary

The stretch-shortening cycle (SSC) is a fundamental mechanism in explosive human movement, enabling musculotendinous units to store and release elastic energy, thereby allowing the body to produce higher forces and velocities with greater mechanical efficiency. Movements such as sprinting, jumping, hopping, and sudden changes of direction, which depend on rapid force application, are supported by an effective SSC. Because of this, identifying a simple and interpretable index of SSC function has long been a priority in both research and applied sport settings. The Reactive Strength Index (RSI), most commonly defined as the ratio of jump height to ground contact time, has become the most widely used metric for quantifying SSC performance. However, this ratio presents notable methodological limitations: it combines variables of incompatible dimensions and is insensitive to drop height, thereby ignoring the eccentric load imposed on the musculotendinous system. The Dynamic Rebound Index (DRI), recently proposed as a dimensionless and mechanically grounded alternative, is calculated as DRI = (box height + jump height) / (9.8 × ground contact time²). Despite its theoretical advantages, a direct comparison between the RSI and DRI remains unexplored in the literature, which justifies the relevance of the present study. This study aims to compare the RSI and the DRI in physically active adults of both sexes during the execution of the Drop Jump at four different drop heights (20, 30, 40, and 50 cm). The specific objectives are: (a) to characterize performance across the four height conditions; (b) to analyze differences between sexes in both indices; (c) to examine the effect of drop height on both indices; and (d) to explore the informative complementarity between the two indices.

Conditions

• Physical Performance Parameters

Interventions

Type	Name	Description
OTHER	Drop Jump Protocol	Participants perform 3 valid Drop Jump trials at each of four drop heights (20, 30, 40, and 50 cm) in a randomized order, with 1 minute of rest between trials and 5 minutes between conditions. Jump height and ground contact time are recorded using a contact mat (ChronoJump, Boscosystem, Spain) for subsequent calculation of the RSI and DRI.

Timeline

• Start date: 2026-03-01
• Primary completion: 2026-07-01
• Completion: 2026-07-01
• First posted: 2026-03-16
• Last updated: 2026-03-16

Locations

1 site across 1 country: Portugal