top of page

Reactive Strength Index, Modified - Fatigue and Performance

GPS DataViz

In 2008 and 2010, Ebben and Petushek introduced the concept of the Modified Reactive Strength Index (RSImod) as a refined measure of explosive power in plyometric exercises, particularly focusing on the countermovement jump (CMJ). Their work aimed to enhance the understanding of how reactive strength could be quantitatively assessed, thereby providing a more nuanced tool for evaluating athletic performance (Ebben & Petushek, 2010). RSImod is calculated by dividing jump height by time to take off (during the CMJ on dual force plates), which allows for a better assessment of an athlete's ability to generate force rapidly during the stretch-shortening cycle (Ebben & Petushek, 2010)


Ebben and Petushek's study emphasized the importance of this index in evaluating various plyometric exercises, asserting that it could serve as a reliable indicator of explosive power across different populations, including both male and female athletes (Ebben & Petushek, 2010). They conducted tests involving a variety of plyometric movements, which demonstrated that RSImod could effectively differentiate performance levels among athletes, thus offering coaches and trainers a valuable metric for monitoring fatigue levels and performance (Ebben & Petushek, 2010; Suchomel et al., 2015).


Furthermore, the authors highlighted the RSImod's potential to assess differences in explosive strength, suggesting that it could be a useful tool for tailoring training programs to meet the specific needs of different athletes (Ebben & Petushek, 2010). This aspect of their research aligns with subsequent studies that have validated the RSImod as a reliable measure of explosiveness in various sports contexts, reinforcing its applicability in strength and conditioning practices (Suchomel et al., 2015; Kipp et al., 2016).


Ebben and Petushek's work in 2008 and 2010 laid the groundwork for the Modified Reactive Strength Index (RSImod) as a critical tool in sports science and strength and conditioning, enabling a more detailed analysis of explosive performance and providing insights into the effects of training and fatigue on athletic capabilities.


Fatigue:


“Even though jump height may remain constant, the contraction time (time to take off) may vary, it is this relationship that can be used to evaluate levels of fatigue or readiness” Sasha Birge via VALD Performance


Research indicates that RSImod is sensitive to changes in an athlete's performance due to fatigue. Fatigue, a critical factor in athletic performance, can significantly impact RSImod values. As athletes fatigue, their ability to generate force and power diminishes, which can lead to a decrease in jump height and an increase in time to take off (McMahon et al., 2018; Nishiumi et al., 2023).  This relationship underscores the importance of monitoring RSIMod as a means to assess not only explosive strength but also the effects of fatigue on performance.


Studies have shown that as fatigue accumulates, there are observable declines in RSImod scores, which correlate with decreased explosive performance (Philipp, 2024; , Guthrie et al., 2022). This relationship is crucial for sport coaches and strength and conditioning coaches, as it allows them to identify when an athlete may be overreached or at a potential risk of injury due to fatigue. 


The ability to monitor fatigue through RSImod can be enhanced by integrating it with other performance metrics. For example, combining RSImod with flight time to contraction time ratios can provide a more comprehensive view of an athlete's neuromuscular status (Heishman et al., 2019). Additionally, breaking down time to take off into three categories - unweighting time, eccentric/braking time and concentric/propulsive time will allow the practitioner more insight into which phase of the jump may be impacted by fatigue and in-turn provide a training intervention.


Employing RSImod alongside subjective measures of fatigue and recovery, such as the Rating of Perceived Exertion (RPE), can further refine the assessment of an athlete's readiness to perform (Knowles et al., 2022; , Oliver et al., 2015). This multifaceted approach to monitoring fatigue is particularly beneficial in athletics, where external and internal  training loads can vary significantly and athletes are often balancing academic and athletic commitments.


“The human body is tremendously resourceful when it comes to accomplishing a physical task, however, the strategy for achieving that task, can look a whole lot different when we are fatigued” Sasha Birge via VALD Performance


RSI-Mod Made Simple - VALD Performance
RSI-Mod Made Simple - VALD Performance

Performance:


The Modified Reactive Strength Index (RSImod) has emerged as a significant metric in sports science for assessing and enhancing athletic performance, particularly in explosive movements such as jumping


Research has demonstrated that improvements in RSImod are closely associated with enhanced performance in various sports. For instance, Kipp et al. validated RSImod as a reliable measure of explosiveness in collegiate female volleyball players, highlighting its effectiveness in differentiating performance across various plyometric exercises, including the countermovement jump (CMJ) and squat jump (Kipp et al., 2016). This validation underscores the index's utility in monitoring training adaptations and performance gains, as athletes with higher RSImod scores typically exhibit superior jumping abilities and overall athletic performance (Kipp et al., 2016; Kozinc et al., 2022).


Moreover, studies have indicated that specific training regimens targeting reactive strength can lead to significant increases in RSImod. For example, Bouguezzi et al. found that prepubertal male soccer players demonstrated substantial gains in RSImod after engaging in training that emphasized SSC actions, suggesting that such training effectively enhances the ability to produce maximal strength in minimal time (Bouguezzi et al., 2019). This aligns with the findings of Ramírez-Campillo et al., who noted that plyometric training significantly improved RSImod and related performance metrics in young soccer players (Ramírez‐Campillo et al., 2018).


The relationship between RSImod and performance extends beyond jumping ability; it also correlates with other athletic capabilities such as sprinting. Sarvestan et al. posited that RSImod serves as a reliable parameter for monitoring jump performance, which can indirectly influence other athletic skills, including volleyball spike jump height (Sarvestan et al., 2020). This suggests that improvements in RSImod can have a cascading effect on overall athletic performance, making it a valuable focus for training programs.


In conclusion, RSImod is a valuable metric for evaluating athletic performance, particularly in explosive movements. Its ability to reflect both the force and time characteristics of jumps makes it a comprehensive tool for assessing an athlete's reactive strength and potential injury risk. As such, it is increasingly utilized in sports science for monitoring training adaptations and guiding rehabilitation protocols.


RSI Mod - Performance norms


Sole, Suchomel, & Stone (2018)
Sole, Suchomel, & Stone (2018)
Sole, Suchomel, & Stone (2018)
Sole, Suchomel, & Stone (2018)

Conclusion

RSImod (Reactive Strength Index Modified) is a valuable metric for assessing athletic performance and fatigue levels. It provides insights into an athlete's explosive strength and neuromuscular status by measuring the relationship between jump height and time to take off. As fatigue accumulates, RSImod scores typically decline, indicating decreased explosive performance and potential increased injury risk


By utilizing RSImod as part of a multifaceted approach to performance monitoring, coaches can effectively assess training adaptations, guide rehabilitation protocols, and optimize athletic performance while minimizing the risk of overreaching or injury due to fatigue.


References:


Petridis, L., Tróznai, Z., Pálinkás, G., Kalabiska, I., & Szabó, T. (2017). Modified reactive strength index in adolescent athletes competing in different sports and its relationship with force production. American Journal of Sports Science and Medicine, 5(2), 21-26. 


Heishman, A., Brown, B., Daub, B., Miller, R., Freitas, E., & Bemben, M. (2019). The influence of countermovement jump protocol on reactive strength index modified and flight time: contraction time in collegiate basketball players. Sports, 7(2), 37. 


Ebben, W. P. and Petushek, E. J. (2010). Using the reactive strength index modified to evaluate plyometric performance. Journal of Strength and Conditioning Research, 24(8), 1983-1987. 


Philipp, N. M., Nijem, R. M., Cabarkapa, D., Hollwedel, C. M., & Fry, A. C. (2024). Investigating the stretch-shortening cycle fatigue response to a high-intensity stressful phase of training in collegiate men's basketball. Frontiers in Sports and Active Living, 6.


Guthrie, B. M., Jagim, A. R., & Jones, M. (2022). Ready or not, here i come: a scoping review of methods used to assess player readiness via indicators of neuromuscular function in football code athletes. Strength &Amp; Conditioning Journal, 45(1), 93-110. 


Kipp, K., Kiely, M. T., & Geiser, C. (2016). Reactive strength index modified is a valid measure of explosiveness in collegiate female volleyball players. Journal of Strength and Conditioning Research, 30(5), 1341-1347. 


Suchomel, T., Bailey, C., Sole, C., Grazer, J., & Beckham, G. (2015). Using reactive strength index-modified as an explosive performance measurement tool in division i athletes. The Journal of Strength and Conditioning Research, 29(4), 899-904. 


Sole, C. J., Suchomel, T. J., & Stone, M. H. (2018). Preliminary Scale of Reference Values for Evaluating Reactive Strength Index-Modified in Male and Female NCAA Division I Athletes. Sports, 6(4), 133


Knowles, O., Drinkwater, E., Roberts, S., Alexander, S., Abbott, G., Garnham, A., … & Aisbett, B. (2022). Sustained sleep restriction reduces resistance exercise quality and quantity in females. Medicine & Science in Sports & Exercise, 54(12), 2167-2177.


Sarvestan, J., Svoboda, Z., & Claudino, J. (2020). Force-time curve variables of countermovement jump as predictors of volleyball spike jump height. German Journal of Exercise and Sport Research, 50(4), 470-476.


McMahon, J., Lake, J., Dos’Santos, T., Jones, P., & Comfort, P. (2020). Countermovement jump standards in rugby league: what is a “good” performance?. The Journal of Strength and Conditioning Research, 36(6), 1691-1698.


Maestroni, L., Turner, A., Papadopoulos, K., Cohen, D., Sideris, V., Graham-Smith, P., … & Read, P. (2023). Comparison of strength and power characteristics before acl rupture and at the end of rehabilitation before return to sport in professional soccer players. Sports Health a Multidisciplinary Approach, 15(6), 814-823.


Krzyszkowski, J., Chowning, L., & Harry, J. (2020). Phase-specific predictors of countermovement jump performance that distinguish good from poor jumpers. The Journal of Strength and Conditioning Research, 36(5), 1257-1263.


Jordan, M., Morris, N., Nimphius, S., & Aagaard, P. (2022). Attenuated lower limb stretch-shorten-cycle capacity in acl injured vs. non-injured female alpine ski racers: not just a matter of between-limb asymmetry. Frontiers in Sports and Active Living, 4.


Hughes, W. (2024). The strength characteristics of elite and subelite female gaelic football players. The Journal of Strength and Conditioning Research, 38(6), 1072-1081.

191 views0 comments

Comments


Discover all that GPS DataViz can offer your program

bottom of page