Reactive Strength and Dynamic Rebound: A Drop Jump Index Comparison

NCT07475078 | Not Yet Recruiting

• 1 other identifier: DRI_HS_01
• Study Type: interventional
• Target: 50
• Locations: 1 country
• Sites: 1

Brief 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

Outcome Measures

Primary Outcomes (2)

• Reactive Strength Index (RSI)

  Calculated as RSI = jump height (m) / ground contact time (s), measured during the Drop Jump at four drop heights (20, 30, 40, and 50 cm).

  Baseline

• Dynamic Rebound Index (DRI)

  Calculated as DRI = (box height (m) + jump height (m)) / (9.8 × ground contact time² (s)), measured during the Drop Jump at four drop heights (20, 30, 40, and 50 cm)

  Baseline

Secondary Outcomes (2)

• Jump Height

  Baseline

• Ground Contact Time

  Baseline

Study Arms (4)

Drop Jump 20 cm

EXPERIMENTAL

Participants perform 3 valid Drop Jump trials from a 20 cm drop height

Other: Drop Jump Protocol

Drop Jump 30 cm

EXPERIMENTAL

Participants perform 3 valid Drop Jump trials from a 30 cm drop height

Other: Drop Jump Protocol

Drop Jump 40 cm

EXPERIMENTAL

Participants perform 3 valid Drop Jump trials from a 40 cm drop height

Other: Drop Jump Protocol

Drop Jump 50 cm

EXPERIMENTAL

Participants perform 3 valid Drop Jump trials from a 50 cm drop height

Other: Drop Jump Protocol

Interventions

Drop Jump Protocol OTHER

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.

Also known as: DJ

Drop Jump 20 cm; Drop Jump 30 cm; Drop Jump 40 cm; Drop Jump 50 cm

Eligibility Criteria

• Age: 18 Years+
• Gender Eligibility Details: Biologically Male or Female
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)

You may qualify if:

• Aged 18 years or older.
• Physically active (engaging in regular physical activity at least 3 times per week - minimum of 180 min of physical activity).

You may not qualify if:

• Any musculoskeletal injuries at the time of data collection.
• Any medical condition that could compromise physical performance or safety during testing.

Sponsors & Collaborators

• University Institute of Maia: lead

Study Sites (1)

University of Maia

Maia, Porto District, 4475-690 Maia, Portugal

Location

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: NONE
• Purpose: OTHER
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Principal Investigator

Model Details: All participants will perform Drop Jump trials at four drop heights (20, 30, 40, and 50 cm) in a randomized order within a single experimental session.

Study Record Dates

• First Submitted: March 10, 2026
• First Posted: March 16, 2026
• Study Start: March 1, 2026
• Primary Completion: July 1, 2026
• Study Completion: July 1, 2026
• Last Updated: March 16, 2026

Record last verified: 2026-03

Locations

PT (1)