Drop Jump Test - DJ

Also called Reactive Strength Test: evaluates reactive force and Reactive Strength Index (RSI).

Drop Jump Test (DJ)

Test Objective

To evaluate reactive strength (Reactive Strength Index - RSI), which is the ability to produce an explosive force in a very short amount of time in response to a stimulus (the drop).

Required Equipment

  • Force platform or contact mat (e.g., Optojump, Chronojump, etc.).
  • A plyometric box or step (height ranging between 20 and 60 cm depending on the athlete's level).
  • A flat, stable, and safe surface.
  • Software or an assistant to analyze the data.

Test Protocol

  • The subject stands upright on a box of a predefined height (e.g., 30 cm).
  • They drop forward off the box (strictly without jumping upward), keeping their feet parallel.
  • Upon making contact with the ground, they must immediately execute a maximal vertical jump as quickly as possible (minimizing ground contact time with no pause).
  • Arm positioning can be:
    • Fixed on the hips (standardized version for strict lower-limb isolation).
    • Free swinging (a more functional, sport-specific version).
  • The measurement system records:
    • Ground contact time.
    • Jump height.

Evaluation

  • Calculation of the Reactive Strength Index (RSI):

    RSI = Jump height (cm) / Contact time (seconds)

  • A high RSI value indicates superior reactive capacity (a combination of strength and reaction speed).
  • The athlete performs 3 trials, and the best RSI score is recorded.

Interpretation of Results

RSI ValueInterpretation
< 1.5Poor reactive strength (indicates a need to work on fast plyometrics).
> 2.5Excellent reactivity (typical of explosive athletes, sprinters, and jumpers).

(Note: The DJ is highly sensitive to neuromuscular fatigue, making it a critical test for training load monitoring and recovery tracking).

Variations

  • Unilateral Drop Jump: Performed on a single leg.
  • Incremental Drop Jumps: Dropping from different heights (e.g., 20, 30, 40, and 50 cm) to construct a complete plyometric profile.
  • DJ with RSI targets: Using the RSI output as real-time biofeedback during training.

Recommendations

  • Ensure a thorough warm-up prior to the test (including light plyometrics and muscle activation).
  • Start with a lower box height (20–30 cm) to mitigate the risk of injury.
  • Always standardize the conditions: use the exact same box, equipment, and verbal instructions for every test.

 

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