The Reactive Strength Index (RSI), is a high-quality representation of the overall performance in standardized jump tests of neuromuscular status. There are two methods that coaches use to quantify RSI depending on the test that you use. The first ratio is Jump Height divided by Contact Time in the Drop Jump. You could also use the ratio between Jump Height and Contraction Time in the Countermovement Jump. RSI value is sensitive to meaningful changes in status relating to either of the two variables.
When RSI is below the desired standard, first screen for context:
-Is the score low compared to the athlete’s normal numbers or low compared to teammates?
-Is the low score a one-off or a trend?
-Were any dynamics of the testing procedure outside of standard practice? Examples include an insufficient warmup, reduced number of trials or a stressful prior meeting.
If there is a contextually relevant downward trend, coaches can take several steps to further evaluate and address the issue. The first step is a simple discussion to understand or rule-out obvious factors such as poor sleep, high stress, or soreness. I would only recommend this if the athlete-practitioner relationship is excellent. The athlete also needs to be compliant with the program that you’ve assigned. If the athlete isn’t affected by any of the aforementioned issues, take a look at the underlying data. Consider which is below desired standards: Jump Height, or Contraction Time?
If the athlete is not jumping high enough, overall athleticism or training status might be an issue. Contraction time deficits bring more specific physical qualities into focus. Eccentric force production is frequently the most trainable quality effecting overall neuromuscular and specific jump performance. Training and monitoring for eccentric deceleration rate of force development can reduce contraction time without compromising jump height. This can significantly enhance RSI and reduce eccentric duration. Eccentric duration is an obvious first variable to examine upon observing low RSI.
Some exercises to enhance the eccentric deceleration rate of force development, effecting RSI:
-Stiff-leg depth landings
-Repeated hops/”Pogo” jumps
-Drop-catch squats & lunges
-Olympic-style weightlifting derivatives
Note that RSI may be more sensitive during higher load training periods or phases including a significant elastic focus (1). Monitoring RSI responsibly is no different from other factors: identify meaningful magnitudes of change, flag potentially confounding factors, and set desired crucial benchmarks.