Association and Agreement between Reactive Strength Index and Reactive Strength Index-Modified Scores

Abstract

Since the reactive strength index (RSI) and reactive strength index-modified (RSI-mod) share similar nomenclature, they are commonly referred as interchangeable measures of agility in the sports research literature. The RSI and RSI-mod are most commonly derived from the performance of depth jumping (DJ) and countermovement jumping (CMJ), respectively. Given that DJ and CMJ are plyometric movements that differ materially from biomechanical and neuromotor perspectives, it is likely that the RSI and RSI-mod measure distinct aspects of neuromuscular function. The purpose of this investigation was to evaluate the association and agreement between RSI and RSI-mod scores. A mixed-sex sample of NCAA division I basketball athletes (n = 21) and active young adults (n = 26) performed three trials of DJ from drop heights of 0.51, 0.66, and 0.81 m and three trials of countermovement jumping. Using 2-dimensional videography and force platform dynamometry, RSI and RSI-mod scores were estimated from DJ and CMJ trials, respectively. Linear regression revealed moderate associations between RSI and RSI-mod scores (F = 11.0–38.1; R2 = 0.20–0.47; p < 0.001–0.001). Bland–Altman plots revealed significant measurement bias (0.50–0.57) between RSI and RSI-mod scores. Bland–Altman limit of agreement intervals (1.27–1.51) were greater than the mean values for RSI (0.97–1.05) and RSI-mod (0.42) scores, suggesting poor agreement. Moreover, there were significant performance-dependent effects on measurement bias, wherein the difference between and the mean of RSI and RSI-mod scores were positively associated (F = 77.2–108.4; R2 = 0.63–0.71; p < 0.001). The results are evidence that the RSI and RSI-mod cannot be regarded as interchangeable measures of reactive strength.

Association of Body Composition With Leg Strength, Balance Capacity and Drop Jump Ability in Capoeira Athletes: A Pilot Study

“…We also reported that RSI was associated with LM and there was a significant negative correlation between drop jump and FM, indicating excess FM is a significant factor affecting jumping ability in capoeira athletes. It is well documented that RSI is an important indicator of the stretch-shortening cycle (SSC) efficiency, defined as muscle action when active muscle lengthening is immediately followed by active muscle shortening (Louder, Thompson, & Bressel, 2021;Seiberl, Hahn, Power, Fletcher, & Siebert, 2021). For example, Flynn (Flynn, 2016) reported that RSI was negatively associated with percent FM and body weight, which is in line with the findings of the current study, indicating the role of excess body weight in jumping ability.…”

Kinetics of Depth Jumps Performed by Female and Male National Collegiate Athletics Association Basketball Athletes and Young Adults

“…All three trials were performed at a given height before proceeding to the next condition. The selection of drop heights was informed by a meta-analysis [ 52 ] that reported that plyometric training interventions may include DJs performed from drop heights ranging between 0.12 and 1.10 m. Additionally, in our recent work [ 53 ], we observed that GCTs were not significantly impacted when DJs were performed from the range of drop heights included in the current investigation.…”

Comparing autoregulatory progressive resistance exercise and velocity-based resistance training on jump performance in college badminton athletes

“…Young (1995) proposed the RSI as a measure of the ability to quickly transition from eccentric to concentric muscle contractions during jumping. The RSI is calculated as the jump height during a DJ divided by the contact time ( Louder, Thompson & Bressel, 2021 ). Improvement of the RSI can be achieved by increasing jump height and decreasing contact time.…”