DRI: the new index to measure vertical jump better than RSI

Updated on 26 de June de 2026 by Adrián Escobar Morales

If you have been using the vertical jump as an evaluation and monitoring tool for some time, you know well the RSI (Reactive Strength Index). For years it has been the reference metric to assess the reactive capacity of an athlete in exercises such as the drop jump. But he has a problem that every coach ends up noticing in practice: not all high RSIs mean the same.

An athlete can obtain a high RSI simply because he or she has a very short contact time, even if his jump height is mediocre. Another may have a moderate RSI with a really efficient combination of contact and height. Which of the two is using the stretch-shortening cycle better? The RSI doesn’t always tell you apart.

In January 2026, researcher Lance Christian Brooks, from Bridgewater State University (USA), published a study in the European Journal of Sport Sciences proposing a more solid alternative: the DRI (Dynamic Rebound Index). The study has already accumulated more than 5,000 readings and 2,800 downloads, which gives an idea of ​​the interest it has generated in the scientific and applied community.

The Stretch-Shortening Cycle: What We Really Evaluate

Before talking about metrics, it is important to be clear about what we want to measure. He stretch-shortening cycle (SSC) It is the ability of the musculotendinous system to store elastic energy during the eccentric phase (landing) and release it quickly and efficiently in the concentric phase (takeoff).

This ability is essential in any sport that involves jumps, sprints, changes of direction or explosive actions. The athlete who best exploits the SSC does not need to activate more muscle — he needs to activate it better and faster, taking advantage of the energy already stored in tendons and elastic elements.

The problem is that SSC cannot be measured directly. We need an indicator — a proxy — that indirectly tells us how well the athlete is using it. Both the RSI and the DRI are just that: proxies for the SSC. The question is which represents it best.

The RSI: useful but with an important blind spot

The RSI is calculated by dividing the jump height between contact time:

RSI = jump height (m) / contact time (s)

Its great advantage is simplicity: with two easy-to-measure variables you obtain a number that gives an idea of ​​the athlete’s reactive capacity. That’s why it became so popular. But Brooks’ (2026) study precisely identifies three structural limitations that explain why that number can be misleading.

1. Dimensional incompatibility

Height divided by time produces units of velocity (m/s), but RSI is interpreted as a dimensionless index of performance. This inconsistency is not a minor detail: it means that the index does not represent a well-defined physical property. It is an arbitrary ratio between two magnitudes that should not be related in that way.

2. Contact time hypersensitivity

Since the contact time is in the denominator, very small values ​​trigger the RSI disproportionately. An athlete who touches the ground very briefly — even if he barely rises — can get a very high RSI. Brooks demonstrates it clearly: the RSI rewards joint stiffness without effective production of mechanical work, which is not the same as an efficient SSC.

3. Completely ignore drop height

In a drop jump, the athlete falls from a certain height before jumping. This fall imposes a specific eccentric demand: the greater it is, the more energy the musculotendinous system must absorb and reverse. The RSI ignores this completely — it evaluates a drop jump from 20 cm the same as from 50 cm, as if the mechanical challenge were identical. According to the study, RSI surfaces are identical regardless of the drop height, confirming this insensitivity.

The DRI: what changes and why it matters

He Dynamic Rebound Index (DRI) arises from a fundamental question posed by Brooks: how to express performance in the SSC while respecting the kinematic laws of vertical movement?

The answer starts from a basic physical relationship: displacement under constant acceleration scales with the square of time, not linearly. Based on this, the DRI is defined as:

DRI = (h_jump + h_fall) / (g × t_contact²)

Where:

• h_jump = jump height (meters)
• h_fall = fall height in the drop jump (meters; zero in CMJ)
• g = gravitational acceleration (9.81 m/s²)
• t_contact = contact time (seconds)

At first glance it seems more complex than the RSI, but its logic is elegant. Each term has a specific role.

The numerator: the total travel demand

The term h_jump + h_fall reflects the total vertical displacement that the athlete must manage in that drop jump. Not only does it count where it goes up, but also where it came from. An athlete who falls from 40 cm and rises 30 cm has to manage 70 cm of total displacement — and the DRI recognizes this. The RSI only sees the 30 cm rise.

The denominator: correctly scaled time

In physics, displacement under constant acceleration scales with the square of time. The DRI incorporates g × t_contact² in the denominator, respecting this relationship. This means that very short contact times without corresponding displacement do not artificially inflate the index. The DRI requires that if the contact is short, the total displacement also be proportionally large.

Truly dimensionless

The numerator has units of meters and so does the denominator (g × t² = m/s² × s² = m). The result is a pure number, without units. This makes the DRI comparable between athletes, between sessions, and between studies in a rigorous way — something that the RSI does not allow.

What the Brooks study found: the key findings

Brooks evaluated the behavior of both indices using computational models that covered representative ranges of contact time (0.10-0.30 s), jump height (0.10-1.00 m) and fall height (0.20-0.50 m). The results were consistent in all analyses:

• RSI surfaces were identical for all drop heights — the index is completely insensitive to eccentric demand, regardless of what height the athlete falls from.
• DRI surfaces changed systematically with the drop height: the greater the drop, the greater the range and curvature, reflecting the real increase in mechanical demand.
• The RSI assigned high values ​​to low-displacement rigid bounces — very short contacts with low jump height obtained high RSI. The DRI maintained low values ​​under those same conditions.
• The DRI distinguished between “rigid” strategies and “effective” strategies.: only increased when short contacts were accompanied by large total displacements.

The conclusion of the study is clear: the DRI maintains the measurement simplicity of the RSI — same field variables, without the need for new instrumentation — but offers a mechanically coherent representation of the SSC.

What practical difference is there between using RSI and DRI

Let’s imagine two athletes doing a drop jump from 40 cm:

• Athlete A: contact time 0.16 s, jump height 18 cm.
• Athlete B: contact time 0.22 s, jump height 32 cm.

With the RSI, athlete A obtains a higher value (0.18/0.16 = 1.13 vs. 0.32/0.22 = 1.45 — in this case B wins, but if A had 0.12 s of contact with only 15 cm of height, his RSI would be 1.25, surpassing B). With the DRI, athlete B is always better valued because he generates more total displacement in relation to the contact time squared, considering the demand of the fall.

From the mechanics of the movement, Athlete B is absorbing more energy from the fall and converting it into jump height more efficiently. The DRI consistently recognizes this; the RSI may not depending on contact times.

This difference has direct implications in practice:

• Classification and selection of athletes: The ranking may change depending on the index you use. An athlete who appears reactive with RSI may be less efficient with DRI if his or her reactive ability is based on stiffness rather than effective displacement production.
• Load progression in plyometrics: If you use RSI to decide when to increase drop height, you may be relying on a parameter that does not accurately reflect the athlete’s actual ability to handle that additional eccentric demand.
• Fatigue monitoring: The DRI may be more sensitive to actual changes in neuromuscular function because it is not distorted by small variations in contact time.

When to use RSI and when to use DRI?

Situation	RSI	DRI
CMJ or jumps without prior landing	Valid	Equivalent (h_fall = 0)
Drop jumps with variable drop height	Limited — ignores drop	Recommended
Compare athletes with very different contact times	Risk of bias	More reliable
Fast session-by-session monitoring	Valid for simplicity	Valid with more context
Advanced Plyometrics Assessment	Insufficient	Recommended

For jumps without drop (CMJ, SJ), the DRI and RSI converge because h_drop is zero. The real difference appears in the drop jumps, which are precisely where the SSC is evaluated most specifically.

How to calculate DRI with ADR Jumping data

The DRI needs three variables: jump height, contact time and drop height. The first two are measured by ADR Jumping automatically with each jump and are registered in the app ADR System. The third — the drop height — is defined by you when configuring the protocol.

With those three pieces of information, the formula in a spreadsheet is:

DRI = (h_jump + h_fall) / (9.81 × t_contact²)

A concrete example: drop jump from 40 cm (0.40 m), jump height 0.30 m, contact time 0.22 s:

DRI = (0.30 + 0.40) / (9.81 × 0.22²)
DRI = 0.70 / (9.81 × 0.0484)
DRI = 0.70 / 0.4748
DRI ≈ 1.47

Brooks further notes that DRI can be calculated in three different ways — from contact time and jump height, from flight time, or from force platform data — making it compatible with different types of instrumentation without needing to change the protocol.

Conclusion

The RSI was for years the best option available to quantify reactive capacity in jumping. It is still useful, especially for jumps without a fall and for quick monitoring where simplicity is a priority. But the study by Brooks (2026) rigorously demonstrates that, in the context of plyometric training with drop jumps, the RSI presents structural limitations that can lead to incorrect interpretations: it rewards short contacts without effective production of mechanical work and completely ignores the eccentric demand of the fall.

The DRI solves these problems without adding complexity to the measurement — same variables, different formula — and offers a representation that respects the physical laws of vertical movement. It’s not about adding another metric, but rather making sure that the number you use to make training decisions reflects what you think it is reflecting.

Literature

Los siguientes estudios respaldan los datos y conclusiones de este artículo sobre el DRI y la evaluación del ciclo de estiramiento-acortamiento:

1. Brooks, L.C. (2026). A Unified Mechanical Framework for Evaluating Stretch–Shortening Cycle Function. European Journal of Sport Sciences, 5(1), 1–10. See study →
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 and Conditioning Journal, 30(5), 32–38. See study →
3. Healy, R., Kenny, I.C. & Harrison, A.J. (2018). Reactive strength index: A poor indicator of reactive strength? International Journal of Sports Physiology and Performance, 13(6), 802–809. See study →