(17) RELATIONSHIP BETWEEN BALANCE SWAY VELOCITY AND MODIFIED REACTIVE STRENGTH INDEX IN A COLLEGIATE WOMEN’S BASKETBALL TEAM

Background: Increased postural sway during quiet standing tasks may serve as a useful indicator for neuromuscular fatigue, reflecting its impact on balance ability. Modified reactive strength index (RSI_mod) quantifies an athlete’s ability to dynamically change direction post-jump, while adjusting for body mass, making it a key metric for plyometric performance and recovery monitoring. However, there is limited research examining the relationship between neuromuscular fatigue, as represented by balance sway velocity (B_sv), and RSI_mod.

Purpose: To examine the extent to which RSI_mod can be predicted by mean B_sv, and to compare RSI_mod and B_sv metrics between high- and low-minute players across a women’s collegiate basketball season.

Methods: National Collegiate Athletic Association Division I women’s basketball athletes (n=14) participated. Athletes underwent weekly unilateral B_sv and bilateral RSI_modassessments on force plates from August to February (n=25). B_sv was calculated as the average of two 5-second trials per leg, resulting in a single value for each athlete observation. High-minute players were classified as those who played ≥15 minutes per game (n=8); others were classified as low-minute players (n=6). A linear regression model was used to assess the predictive relationship between B_sv and RSI_mod. R² effect sizes were determined and classified as: r²=0.01, small effect; r²=0.09, medium effect; and r²=0.25, large effect. Multivariate analysis of variance (MANOVA) assessed differences in B_sv and RSI_mod between high- and low-minute players (p< 0.05). η² effect sizes were determined and classified as: η²=0.01, small effect; η²=0.06, medium effect; and η²=0.14, large effect.

Results: Figure 1 shows a scatterplot of the regression analysis, along with the distribution of observations for high- and low-minute players. Regression analysis indicated that B_sv is significant in predicting RSI_mod (r= –0.407, R²=0.166, F(1.142, 0.004) = 319.47, p< 0.001. Additionally, MANOVA analysis showed that RSI_mod was significantly greater for high-minute players (mean ± SD: 0.399 ± 0.06; 95% CI: 0.396–0.403) than low-minute players (0.359 ± 0.07; 95% CI: 0.354–0.364) (p< 0.001; η²=0.083). Similarly, B_sv was significantly greater for high-minute players (0.029 ± 0.008 m/s; 95% CI: 0.028–0.029) than low-minute players (0.027 ± 0.08 m/s; 95% CI: 0.027–0.028) (p< 0.001; η²=0.007).

Conclusions: Findings suggest that increases in fatigue-induced postural sway velocity result in an attenuated RSI_mod. Further, despite exhibiting higher B_sv, high-minute players demonstrate superior RSI_mod compared to low-minute players. PRACTICAL APPLICATIONS: Force plate balance assessments offer a non-orthopedically stressful method for evaluating neuromuscular recovery, and they hold potential for predicting how fatigue might impact more dynamic, sport-specific assessments like RSI_mod. Additionally, it is advised to prioritize recovery for high-minute players during the season.


Acknowledgements: None