This procedure describes the method used for measuring reactive leg strength using the Drop Jump, where the athlete jumps after a drop from a series of heights, starting from a 30cm box and working upwards to a 75cm box. There is also a drop jump test as part of the Bosco Ergo Jump System. See about other vertical jump tests.

How to Use This Calculator

Follow these steps to accurately measure your reactive strength index:

  1. Select the Drop Height - Choose the box height you're testing from (30cm, 45cm, 60cm, or 75cm). For comprehensive assessment, test all four heights.
  2. Perform the Drop Jump - Step off the box, land on the timing mat, and immediately jump vertically as high as possible.
  3. Record Your Data - Enter the flight time (time in air) and ground contact time displayed by your measurement device.
  4. Calculate Results - Click "Calculate RSI" to see your jump height and reactive strength index.
  5. Compare Heights - Click "Add to Comparison" after each height to build a complete profile and identify your optimal drop height.

Pro Tip: Your optimal drop height for training is the height at which you achieve your highest RSI score. This represents where you can most efficiently convert eccentric loading into explosive power.

Test Protocol and Equipment

Purpose: To measure the reactive strength index of the lower limbs across multiple drop heights, identifying the optimal height for plyometric training.

Equipment required: Vertical jump measurement mat (e.g., just jump mat, Myotest, infrared laser system), boxes or elevated platforms of different heights: 30 cm, 45 cm, 60 cm, 75 cm.

Pre-test preparation: Explain the test procedures to the subject. Perform screening of health risks and obtain informed consent. Prepare forms and record basic information such as age, height, body weight, gender, test conditions. Check and calibrate the timing mat measurement. Subject to perform an appropriate warm-up. See more details of pre-test procedures.

drop jump test

Procedure: A drop jump is performed from a range of box heights (30 cm, 45 cm, 60 cm, 75 cm), starting from the lowest height. The athlete stands on the box adjacent to the timing mat. Hands are placed on the hips, and stay there throughout the jump. The athlete steps down off the box onto the mat, bending the knees on landing, then immediately going into a maximal vertical jump. The athlete jumps vertically as high as possible, and lands back on the mat with both feet landing at the same time. The test is repeated for increasing box heights, for example using 30 cm, 45 cm, 60 cm, 75 cm boxes. Allow an adequate rest between trials.

Understanding Your Results

The RSI Formula

Reactive Strength Index is calculated using two measurements:

RSI = Jump Height (m) ÷ Ground Contact Time (s)

Jump height is derived from flight time:

Jump Height = 4.9 × (0.5 × Flight Time)²

Where 4.9 m/s² is half the acceleration due to gravity (9.8/2)

Scoring: Reactive strength index (RSI) can be calculated by dividing the jump height by the ground contact time. The jump height time is the time between the participant's feet leaving the timing mat or force platform and when they contacted it again. The vertical jump height in meters can be calculated from the time (in seconds) using this formula: jump height = 4.9 × (0.5 × Time)². Ground contact time is the time between the first foot contact with the force platform and when the participant's feet left the mat.

Results: If an athlete jumped 36cm with a contact time of 0.18 seconds then they would have an RSI of 2.0 (0.36 ÷ 0.18 = 2.0). The athlete can therefore improve their RSI by increasing the height of their jump, by decreasing their ground contact time, or both of these.

RSI Performance Standards

RSI values vary significantly based on sport, training background, and athletic level:

Elite Level (RSI > 3.0)

Olympic sprinters, elite jumpers, professional basketball players. Exceptional reactive strength capacity.

Advanced Level (RSI 2.0-3.0)

Collegiate athletes, competitive team sport players, trained plyometric athletes.

Intermediate Level (RSI 1.5-2.0)

Regular training athletes, recreational competitors, developing athletes.

Developing Level (RSI < 1.5)

Beginners, athletes returning from injury, those new to plyometric training.

Sport-Specific Applications

Different sports have varying requirements for reactive strength:

Track and Field Sprinters: Elite 100m sprinters typically demonstrate RSI values of 3.0-4.0. The ground contact time during sprinting is similar to that in drop jumps (0.08-0.12s), making this test highly relevant for sprint training prescription.

Basketball and Volleyball Players: Athletes in these sports benefit from optimal RSI at moderate drop heights (45-60cm), as they frequently perform rebounds and blocks requiring quick ground contact transitions.

Football and Rugby Players: Position-specific requirements vary, with backs typically showing higher RSI values (2.5-3.5) compared to linemen (1.8-2.5). Testing helps optimize position-specific plyometric programming.

Soccer Players: Midfielders and wingers often demonstrate RSI values of 2.0-2.8, reflecting the need for quick directional changes and explosive movements during match play.

Training Recommendations Based on Results

If Your RSI is Below 1.5: Focus on developing general strength through squats, deadlifts, and lunges before progressing to intensive plyometrics. Begin with low-intensity jumping drills such as line hops and ankle bounces.

If Your RSI is 1.5-2.0: Incorporate moderate-intensity plyometrics including box jumps, broad jumps, and depth jumps from your optimal height. Maintain strength training while gradually increasing plyometric volume.

If Your RSI is 2.0-3.0: Progress to high-intensity plyometrics and shock training methods. Use your optimal drop height identified through testing for depth jump training. Consider sport-specific reactive drills.

If Your RSI Exceeds 3.0: Maintain reactive strength through quality plyometric sessions. Focus on transferring reactive ability to sport-specific movements and consider weighted plyometrics for continued development.

Advantages and Limitations

Advantages: The incremental drop jump test provides objective measurement of reactive strength capacity across multiple loading conditions. Testing at various heights identifies the optimal training stimulus for each athlete, allowing personalized plyometric programming.

Disadvantages: Drop jumps require athletes to have a good degree of leg strength, as the forces through the body are much higher than for a standard vertical jump test. The standard size boxes are not readily available, and may even need to be custom made. Athletes with lower limb injuries or insufficient base strength should avoid this test.

Comments: Though this is the standard test of reactive strength, there are also other methods to assess an athlete's reactive strength ability. See more about the Reactive Strength Index.