The Bosco Drop Jump test measures leg power and reactive strength using a standardized protocol developed by sports scientist Carmelo Bosco. The athlete drops from specific heights (20, 40, 60, 80, and 100 cm) and immediately performs a maximal vertical jump. This test is part of the Bosco Ergo Jump System and provides valuable data about an athlete's ability to utilize the stretch-shortening cycle under varying eccentric loads.

How to Use This Drop Jump Calculator

Follow these steps to analyze your drop jump performance and determine your optimal training height:

  1. Select Calculator Mode - Choose "Single Height" for individual jump analysis, or "Multi-Height Comparison" to test across all five Bosco protocol heights and find your optimal drop height.
  2. Enter Flight Time - Input the time in the air (from takeoff to landing) measured by your timing mat. Typical values range from 0.35-0.65 seconds for trained athletes.
  3. Enter Ground Contact Time - Input the time spent on the ground during the reactive jump. Fast SSC activity requires contact times below 0.250 seconds.
  4. Review Your Results - The calculator displays jump height, RSI, takeoff velocity, and performance interpretation with training recommendations.

Pro Tip: For accurate testing, perform 3-5 trials at each height and use the best result. Ensure adequate rest (2-3 minutes) between maximal efforts to prevent fatigue affecting results.

What is Reactive Strength Index (RSI)?

Reactive Strength Index (RSI) measures an athlete's ability to rapidly change from eccentric (lengthening) to concentric (shortening) muscle action during plyometric activities. Developed as part of the Strength Qualities Assessment Test (SQAT) at the Australian Institute of Sport, RSI has become the gold standard for assessing fast stretch-shortening cycle function.

RSI is calculated by dividing jump height by ground contact time:

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

A higher RSI indicates superior reactive strength—the athlete can absorb eccentric forces efficiently and redirect them into powerful concentric output. This quality is essential for sprinting, jumping, and rapid change of direction in virtually all sports.

Why RSI Matters for Athletes

  • Sprint Performance - Ground contact during sprinting ranges from 0.08-0.12 seconds at maximum velocity. High RSI indicates the ability to produce force within these brief contact periods.
  • Jump Performance - Athletes with higher RSI demonstrate better ability to utilize stored elastic energy, translating to more powerful jumps.
  • Change of Direction - Rapid deceleration and reacceleration require excellent reactive strength to minimize ground contact while maximizing force output.
  • Injury Prevention - Adequate reactive strength helps athletes absorb landing forces safely, reducing injury risk during high-impact activities.

The Bosco Drop Jump Formula

Jump height from flight time is calculated using the validated Bosco formula based on projectile motion physics:

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

Where:

  • Jump Height is in meters
  • Flight Time is in seconds
  • 4.9 represents half the acceleration due to gravity (g/2 = 9.81/2)

This formula derives from the kinematic equation for vertical displacement. During flight, the athlete's center of mass follows a parabolic trajectory, reaching zero velocity at the peak. Since time to peak equals half the total flight time, maximum height can be calculated from total flight duration.

Example Calculation

For an athlete with 0.500 second flight time and 0.170 second ground contact time:

  • Jump Height = 4.9 × (0.5 × 0.500)² = 4.9 × 0.0625 = 0.306 m (30.6 cm)
  • RSI = 0.306 ÷ 0.170 = 1.80

This RSI of 1.80 indicates good reactive strength, appropriate for moderate-intensity plyometric training.

RSI Normative Data and Performance Standards

Based on research by Flanagan and extensive testing across multiple sports populations, the following RSI thresholds provide guidance for interpreting drop jump performance:

RSI Score Rating Interpretation
< 1.0 Poor Focus on strength development and plyometric technique before intensive training
1.0 - 1.5 Fair Athlete unprepared for moderate intensity plyometrics; continue strength base
1.5 - 2.0 Good Prepared for moderate intensity plyometrics; can progress training
2.0 - 2.5 Very Good Prepared for intensive plyometrics; can handle high training loads
> 2.5 Excellent Elite reactive strength; may be approaching ceiling for RSI improvements

Sport-Specific RSI Standards

Different sports demonstrate varying RSI requirements based on their movement demands:

  • Track Sprinters: Elite sprinters typically achieve RSI values of 2.5-3.5, reflecting their need for maximal force in minimal ground contact time.
  • Basketball Players: Professional players average RSI of 1.8-2.5, balancing jump height with rapid recovery for rebounding.
  • Soccer Players: Midfielders and forwards typically show RSI of 1.5-2.2, supporting repeated sprint and jump requirements.
  • Volleyball Players: Attackers often demonstrate RSI of 2.0-2.8, maximizing jump height for spike effectiveness.
  • Rugby Players: Backs generally show higher RSI (1.8-2.5) than forwards (1.3-1.8), reflecting position-specific speed demands.

Finding Your Optimal Drop Height

The multi-height Bosco protocol identifies each athlete's optimal drop height for plyometric training. The optimal height produces the highest RSI while maintaining ground contact time below 250 milliseconds—the threshold for fast stretch-shortening cycle activity.

As drop height increases:

  • Eccentric loading forces increase significantly
  • Ground contact time typically increases as the body absorbs greater forces
  • Jump height may increase initially but plateaus or decreases at excessive heights
  • RSI peaks at the height where the athlete can optimally utilize the stretch-shortening cycle

Research by Byrne et al. suggests most athletes find their optimal RSI between 30-60 cm drop heights, though well-trained plyometric athletes may perform optimally at 60-80 cm.

When RSI Decreases

A decline in RSI at higher drop heights indicates the eccentric forces have exceeded the athlete's reactive capacity. At this point:

  • Contact times extend beyond the fast SSC threshold (>250ms)
  • The athlete shifts to slow SSC mechanics
  • Training at these heights becomes counterproductive for developing fast reactive strength

The height before RSI decline represents the training intensity ceiling for that athlete. Plyometric training should remain at or below this height for optimal development.

Test Procedure for the Bosco Drop Jump

Equipment Required:

Pre-Test Procedures:

  • Explain test procedures to the subject and obtain informed consent
  • Perform health screening for musculoskeletal contraindications
  • Record basic information: age, height, body weight, gender, test conditions
  • Calibrate timing mat measurement system
  • Complete thorough warm-up including progressive plyometric preparation

Test Protocol:

  1. Athlete stands on the box adjacent to the timing mat with hands placed on hips
  2. Athlete drops (does not jump) off the box onto the mat
  3. Upon landing, immediately performs a maximal vertical jump using Counter Movement Jump technique
  4. Hands remain on hips throughout the entire movement
  5. Land back on the mat with both feet at the same time
  6. Allow 2-3 minutes rest between trials and heights
  7. Record best of 3 trials at each height

Scoring: The timing mat measures flight time and ground contact time. Jump height is calculated using the Bosco formula: height = 4.9 × (0.5 × Time)². RSI is calculated by dividing jump height by ground contact time.

Training Recommendations Based on RSI

Your RSI results guide appropriate plyometric programming:

RSI Below 1.5 (Focus on Foundation)

  • Prioritize general strength development (squats, deadlifts, lunges)
  • Practice landing mechanics and plyometric technique
  • Use low-intensity plyometrics: skipping, bounding, box jumps with controlled landing
  • Train at 20-30 cm drop heights maximum
  • Volume: 60-80 ground contacts per session, 2x weekly

RSI 1.5-2.0 (Moderate Intensity Training)

  • Progress to moderate intensity drop jumps from 30-40 cm
  • Include depth jump variations with focus on minimal contact time
  • Combine with strength training maintaining 1.5-2x bodyweight squat
  • Volume: 80-100 ground contacts per session, 2-3x weekly

RSI 2.0-2.5 (High Intensity Training)

  • Train at optimal drop height identified through testing
  • Include intensive depth jumps from 40-60 cm
  • Emphasize minimal ground contact time cues
  • Volume: 100-120 ground contacts per session, 2-3x weekly

RSI Above 2.5 (Elite Programming)

  • Focus on maintaining reactive strength while developing other qualities
  • Consider whether further RSI improvement will enhance sport performance
  • May benefit from shock method training at higher drop heights
  • Volume: Variable based on training phase and sport demands

Frequently Asked Questions

How is reactive strength index calculated for drop jumps?

RSI is calculated by dividing jump height (in meters) by ground contact time (in seconds). For example, if you jump 0.35m with 0.18s contact time, your RSI is 0.35 ÷ 0.18 = 1.94. This ratio indicates how efficiently you can absorb landing forces and redirect them into explosive upward movement.

What is a good RSI score for athletes?

RSI varies by sport and training level. Generally, below 1.0 is poor, 1.0-1.5 is fair, 1.5-2.0 is good (appropriate for moderate plyometrics), 2.0-2.5 is very good (ready for intensive training), and above 2.5 is excellent (elite level). Sprinters and jumpers often exceed 2.5, while team sport athletes typically range 1.5-2.5.

How do you find optimal drop height for plyometric training?

Test across multiple heights (20, 40, 60, 80, 100 cm) and calculate RSI at each. Your optimal height is where RSI peaks while contact time remains below 250 milliseconds. When RSI begins to decrease, you've exceeded your reactive capacity. Train at or below this optimal height for best results.

Why does RSI decrease at higher drop heights?

Higher drops create greater eccentric forces that exceed the athlete's ability to rapidly absorb and redirect them. This extends ground contact time faster than jump height increases, causing RSI to decline. This identifies the point where fast stretch-shortening cycle function breaks down.

Can I use flight time instead of jump height to calculate RSI?

Yes, RSI can be calculated as flight time divided by contact time. Since jump height and flight time are mathematically related through the Bosco formula, both methods produce valid results. Flight time is often easier to measure directly from timing mats.

How often should I test drop jump RSI?

Test every 4-8 weeks during training blocks to monitor adaptation. More frequent testing may be appropriate during competition preparation or when monitoring fatigue. RSI is sensitive to neuromuscular fatigue, making it useful for daily readiness monitoring in high-performance settings.