Reactive strength index is a growing topic in sports science research, and has been shown to relate to various important aspects of sports performance. In this article we’re going to answer questions such as:
What is reactive strength index (RSI)?
The reactive strength index (RSI) is a test designed to measure an athlete’s reactive jump capacity, specifically how well an athlete is able to cope with stresses applied through landing in jumping and plyometric activities. It is a ratio of how high an athlete jumps after landing, versus how long they were in contact with the ground. It was first developed in 1995 by Young as part of the Strength Qualities Assessment Test (SQAT) in collaboration with the International Athletics Association.
So, if an athlete is able to jump really high after landing, then they will have a better RSI. Similarly, if an athlete is able to land and jump again very quickly, then they will have a better RSI.
Therefore a better RSI score suggests that an athlete is better able to absorb eccentric forces on landing, effectively utilise their stretch shorten cycle and then produce force concentrically.
Why is reactive strength index important for sport?
RSI in Action
Imagine an athlete with an incredibly poor RSI. Every time they land after a jump it looks awkward and takes them ages to regain their balance and continue with the game. Every time they have to rapidly accelerate and sprint they just look soft, like they’re losing power with every step.
Not only is this athlete going to play worse, but they’re exposing themselves to an increased injury risk every single time that they play.
Now imagine an athlete with an incredibly high RSI. They’re basically a spring in human form. As soon as they land after a jump they’re perfectly balanced and firing off into the next movement. They accelerate with lightning speed, change direction in a flash, and every stride of their sprint seems light and almost effortless.
That’s the importance of the reactive strength index in sport.
RSI in sport performance explained
If we want to be more scientific in our description, RSI is an indicator of an athlete’s ability to switch from an eccentric (muscle lengthening) to a concentric (muscle shortening) contraction, specifically in and around the calf-ankle complex. This means that reactive strength index gives us a good idea as to an athlete’s ability to utilise their stretch-shortening cycle for quick, dynamic and explosive movements such as…
- Change of direction
I.e. the skills essential to the overwhelming majority of team sports, as well as many individual sports too.
How to test reactive strength index?
Whilst there is currently no ‘gold standard’ test for RSI, there are various tests that have been shown to have good validity and reliability.
The most common test is the Incremental Drop Jump Reactive Strength Index test (DJ-RSI).
In which an athlete performs drop jumps from 30cm up to 75cm, or until their ground contact time exceeds the upper limit for fast stretch shortening cycles (0.25s). Typically three efforts would be taken at each box height, so that an average can be calculated.
Alternative reactive strength index tests include…
- Modified RSI test
- Single Vertical Rebound Jump test
- Vertical Rebound Jump for 5-repetitions
- 10/5 test
Pro-Tip: For strength and power athletes, I would recommend the DJ-RSI, whereas for runners or sprint athletes I would recommend the 10/5. Consider the structure of each test to make the best choices for your situation.
How to calculate reactive strength index?
RSI = Jump height / ground contact time. RSI is calculated by dividing the jump height (in meters) by the ground contact time (in seconds). For example, if an athlete jumps 0.389m after a ground contact time of 0.155s, then they have a reactive strength index of 2.51
Reactive strength index formula
Alternative RSI Formulas
RSI = Flight Time / Ground Contact Time
RSI = Jump Height / Time to Take Off
Practical Considerations for reactive strength index calculations
Ideally, jump height would be calculated based on ground reaction forces using a force plate. If this is not possible, alternative options include using a contact mat to find flight time, or using phone based jump tracking technology.
Reactive Strength Index charts
As a coach, I understand the desire to want normative data that I can compare my athletes against. I want to be able to say if they’re doing good, bad or great.
Unfortunately there really isn’t much normative data for reactive strength index tests, and I think that this is for 3 reasons.
- RSI scores vary based on which test is used
- RSI scores vary based on which calculation is used
- RSI scores vary by sport and by player
- RSI scores also vary by flooring and technical execution
So from a practical perspective, it may be FAR more useful to build up your own bank of data for your specific group of athletes.
Now, with all that said, Eamonn Flanagan, PhD, wrote a fantastic article on this topic, in which he used various collected bits of data and personal experience to create a reactive strength index chart.
Another useful set of RSI charts has been constructed by Dr’s Sole, Suchomel and Stone (2018). This data set is specifically for collegiate athletes, and relates specifically to the Modified RSI test. The first chart is for male athletes, the second chart for female athletes.
What is a good reactive strength index?
Well, it depends.
Based on Flanagan’s chart, you could argue that an RSI of 2 and above is a good benchmark for most athletes across a range of sports.
However, you also have to use some common sense and think about your specific sport and athlete. For example, if you’re coaching a sprinter who wishes to compete at world level, then a good score is suddenly much closer to 3 and above.
On the other hand, if you’re coaching a youth athlete in a sport with low RSI demands, then a ‘good’ RSI level might be 1.5
How to improve your RSI
There are three main ways to improve your reactive strength index…
- Jump training
One of the great things about the reactive strength index is that the testing and the training are very closely related. This means that you can use exercises such as drop jumps and vertical jumps to improve your RSI. The key is just to make sure that the jumps you are performing are comfortably within your ability level. So if you had to stop at 60cm drop jumps due to your ground contact times becoming too long, then keep all your drop jump training in the 20-40cm range.
Pro-Tip: With jumps, less is more. 3-5 sets of 3-5 reps a couple of times per week is a really good place to start.
- Strength Development of the calf, leg and hip musculature
The ability to absorb, produce and transmit force is strongly influenced by your muscular strength. Therefore a well-rounded programme of strength training for relevant muscle groups can improve RSI.
I recommend a combination of exercises such as squats, RDL’s, lunges and calf raises. Typically 3 sets of 4-8 reps per exercise once or twice per week is a good starting point for most athletes.
- Bodyweight and body Composition
Since force = mass x acceleration, the heavier you are, the more force your body has to absorb on jump landings. The quickest way to reduce this force and make landings easier is to reduce your bodyweight.
If you’ve been carrying around a few extra pounds or kilos of size that definitely isn’t muscle, then you might want to consider a diet phase to improve your athletic performance.
Validity & Reliability of RSI testing
Whilst there is currently no ‘gold standard’ test for RSI, each of the tests mentioned in this article has been shown to have good validity and reliability.
Issues with the reactive strength index
Technical execution Impacts Scores
For example, performing jumps with hands on hips gives lower scores than using arm swing. A simple solution is to standardise the technique.
Flooring type impacts scores
Softer flooring, e.g. rubber matting, produces lower scores than hard flooring, e.g. wood. A simple solution is to make sure that tests are always conducted on similar flooring. Similarly, it can be useful to ensure that athletes wear standardised shoes, as results may differ slightly in soft running shoes versus firm weightlifting shoes for instance.
Learning Effects impact scores
Athletes new to RSI testing may improve over the first few weeks simply due to learning how to perform the jumps correctly and improving technically – this is know as the learning effect. To avoid issues, a simple solution is to have athletes run a 2-3 week jumping familiarisation block before testing commences.
Reactive strength index is a measure of an athlete’s ability to cope with landing stresses, absorb force and react. It strongly correlates with sporting activities such as jumping, sprinting, accelerating, and changing direction, and RSI can be improved through a combination of jump training, strength training and body composition management.
- If you found this article useful, feel free to share.
- If you want more information on related topics, check out our articles on force-velocity curves and power development.
- Flannagan, E (2021) – The Reactive Strength Index Revisited
- Sole et al. (2018) – Preliminary Scale of Reference Values for Evaluating Reactive Strength Index-Modified in Male and Female NCAA Division I Athletes.
- Young, W. (1995) – Laboratory strength assessment of athletes.
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Alex is the Owner and Head Coach of Character Strength & Conditioning, and specialises in strength & power development for athletes.
He currently works as a Tutor & Educator for British Weightlifting, and has previously delivered S&C support to gymnastics and swimming talent pathways.