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The ability to quickly and efficiently transfer force, known as Reactive Strength, is a vital aspect of athletic performance. It is important for many athletic tasks such as acceleration, sprinting, change of direction, hopping, and jumping. The Reactive Strength Index measures an athlete’s reactive strength. It encompasses the entire Stretch-Shortening Cycle, assessing the athlete’s ability to absorb, amortize (stabilize or control), and produce force.

Reactive Strength Index can be used at various stages of an athletic development program to help coaches assess their athletes and tailor their program to their needs. In this blog, we’ll discuss how you can use the reactive strength index to maximize the development of your athletes and reduce their risk of injury.

Reactive Strength Index and Performance Measures

Reactive strength is a key performance indicator for athletic ability. When compared with other strength and power assessments, it is unique as it involves multiple movements that make up the Stretch-Shortening Cycle (SSC) – an eccentric contraction to absorb and stabilize force, followed immediately by a concentric contraction to produce force. Movements like these are classified as plyometrics.

Movements like these occur frequently and are extremely important in many sports, from side-stepping in rugby, to accelerating in soccer, to slam dunking in basketball, to taking off in the high jump. Therefore, an athlete’s ability to effectively utilize their SSC can be an indicator of athletic and performance capacity.

Studies have shown a moderate correlation between reactive strength index and strength, speed, edurance, and performance, and a large correlation with change of direction and acceleration (Jarvis et al, 2022). More recent studies in Australian Rules Football have also shown a strong correlation between athletes’ reactive strength and offensive and defensive agility (Young et al, 2015).

How can Reactive Strength Index be used?

The reactive strength index can be used at various stages of an athletic development program to assess your athletes and individualize their training to maximize their development and reduce their risk of injury.

Talent Identification

As reactive strength index has been shown to be positively correlated with the performance of a number of movements that are very important in many sports, it can also be used to help with talent identification, especially in sports where these explosive movements are primary attributes. Testing for reactive strength in the talent identification process can identify athletes who may have a predisposition for explosive movements.

Program Individualization

An athlete’s reactive strength index can be used to individualize their athletic development program to maximise their development. Developing an athlete’s reactive strength can improve their performance of specific movements and make them more effective at their sport. Athletes with a low reactive strength index can benefit from plyometric training and other reactive strength training, while athletes with a higher reactive strength index may be better served by fine-tuning their technique in sprint starts and change of direction depending on the sport. The image below presents guidelines on how to individualize an athlete’s program based on their reactive strength index. Click here for more on how to develop your athlete’s reactive strength.

Assessing Readiness, Identifying Overtraining, and Managing Injury Risk

Drop-offs in reactive strength index can be an indicator of muscular fatigue and reduced readiness to train/compete. Testing reactive strength index weekly can highlight drop-offs in performance which alongside internal and external training load measures can identify overtraining and increased injury risk. As highlighted by Matt Jordan in his blog on using reactive strength index data, the most important thing is that we’re “bringing about peak performance when it matters most”, and using reactive strength index as a monitoring tool can enable us to do that by making interventions to manage training load where necessary.

Verifying Overall Program Effectiveness

If you have designed your program to increase your athlete’s reactive strength index, testing for it is essential to confirm that the program has had the desired outcome. It’s important to note that if you’re testing weekly, you may see an initial drop-off in reactive strength index if training loads are high but you should see an increase in reactive strength index when tested at the end of the training cycle. If not, you will need to determine what elements of the program led to its ineffectiveness and redesign for the upcoming training cycle based on your findings.

Providing Athlete Feedback

If you have identified reactive strength index as a key performance indicator for your sport then you should be setting goals with your athletes and tracking their progress over time. Closing the loop here and providing the athletes with individualized feedback is so important to provide them with feedback on what’s working and what they need to give more focus to. Seeing their progress can be a great motivator, as can having open conversations about where they need to improve and how you can help them get there if they’re not achieving their goals.

Rehab and Return-to-Play

Reactive strength can also have a role to play when rehabbing certain injuries and going through return-to-play protocols. Asymmetries in reactive strength are among the most persistent functional deficits after ACL reconstruction even after symmetry is achieved in strength tests (Kotsifaki et al., 2022). This highlights the need for the testing of reactive strength index and the prescription of plyometric exercises to improve reactive strength index during the rehab and return-to-play process to ensure the athlete is ready to train/compete.

Summary

Reactive strength is a vital aspect of athletic performance and its measure, Reactive Strength Index, is strongly correlated with many movements which are central to sports performance like acceleration, sprinting, change of direction, hopping, and jumping. It can be trained and monitored in order to improve sports performance but its value doesn’t end there. It can also be used at various stages throughout the athletic development process such as talent identification, program individualization, assessing readiness, identifying overtraining, managing injury risk, verifying program effectiveness, providing athlete feedback, and during rehab and return-to-play. Make sure you utilize it to maximize your athletes’ development and reduce their risk of injury.

References

• Jarvis, Paul, Turner, Anthony, Read, Paul J ORCID: 0000-00021508-8602 and Bishop, Chris (2022) Reactive Strength Index and its Associations with Measures of Physical and Sports Performance: A Systematic Review with Meta-Analysis. Sports Medicine, 52 (2). pp. 301-330.
• Kotsifaki A, Van Rossom S, Whiteley R, et al. Single leg vertical jump performance identifies knee function deficits at return to sport after ACL reconstruction in male athletes. Br J Sports Med. May 2022;56(9):490-498.
• Young, W.B., Miller, I.R. and Talpey, S.W., 2015. “Physical Qualities Predict Change-of-Direction Speed but Not Defensive Agility in Australian Rules Football.” The Journal of Strength & Conditioning Research, 29(1), pp.206-212.

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