Can you improve your reactive strength index?

For athletes, reactive strength index, or RSI, is a measure of how your body utilizes elastic energy built up in your tendons and muscles during the stretch-shortening cycle. When playing sports or pursuing forms of fitness that might include a quick change of direction or repeated jumps, such as soccer, basketball or football, improving your RSI can help you perform better in your sport.

Marion Kirkland, who works with Apex in Sports Performance, offered some information on how RSI is measured, what RSI tells you about athletic performance, and how to improve it.

How is reactive strength index measured?

“During our initial assessment and later reassessments, I prefer to use the Fusion Sport™ jump mat,” said Kirkland. “Assessing RSI in this manner gives our coaches insight into how rapidly our athletes absorb and redirect force during athletic movements”.

At the start of this RSI test, the athlete stands on the mat, waiting for a green light to appear on a hub connected to it. When the light appears, the individual being tested performs five consecutive pogo-style jumps, with the goal of jumping as high as they can while also spending as little time on the ground as possible between each jump.

Once five jumps are completed, the athlete receives their score, with a higher score representing a better reactive strength index.

This score is calculated by dividing flight time (the time spent in the air) by ground contact time (the time spent in contact with the ground). This means that someone who jumps very high but stays on the ground for an extended time between jumps would receive a low RSI score, just as would someone who gets off the ground quickly but doesn’t jump very high.

What does an RSI value tell you?

“When looking at RSI, what you’re really measuring is your tendon and muscle’s ability to absorb force, and quickly redirect it in a different direction. This is seen in sport when athletes quickly change direction, sprint or perform repeated jumps.”

When landing upon the ground, the tendons and ligaments around your hips, knees, and ankles are lengthened. This temporarily places a stretch on the connective tissue, causing a build-up of elastic energy that is then released in subsequent muscle action. Assessing RSI gives us a tangible number that we can use to determine how efficient an athlete is at using this elastic energy.  

How you improve your RSI?

“There are a lot of exercises you can use to improve your RSI.” said Kirkland. Exercises such as rebound jumps, bounds, power skips, sprints and pogo hops increase ankle and knee tendon stiffness, strength, and resilience, which ultimately can aid in improving reactive strength index.