Dynamic Strength Index and Countermovement Jump Performance in Female and Male Collegiate Basketball Athletes Across a Competitive Season

Abstract

Background: Basketball demands high levels of strength and power for actions such as jumping, sprinting, and changing direction. Monitoring these physical attributes across a competitive season can help inform training strategies. The countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) are widely used to assess power and strength. The Dynamic Strength Index (DSI), calculated as the ratio of CMJ peak force to IMTP peak force, offers insight into the strength–power profile of athletes and may inform individualized training approaches. However, limited research exists on seasonal changes in DSI, CMJ metrics, and joint kinematics in basketball athletes, particularly across time and between sexes. Purpose: This study aimed to compare DSI, CMJ outputs (jump height (JH), reactive strength index modified (mRSI), countermovement depth (CMD), and relative propulsive net impulse (RPNI)), and lower extremity kinematics (hip, knee, ankle) across four timepoints in a competitive basketball season among female and male collegiate athletes. Methods: Twelve female and six male varsity basketball athletes completed CMJ and IMTP assessments at pre-season, early-season, late-season, and off-season timepoints. CMJ outputs were recorded using bilateral force plates (1000Hz, Hawkin Dynamics, ME, USA). Three-dimensional kinematic data were captured through OpenCap (Stanford University, CAL, USA) using two iPads (120Hz; Apple Inc., 7th generation). Mean peak force from CMJ and IMTP trials were used to compute DSI. Mean and standard deviation for DSI, CMJ JH, and bilateral delta ankle dorsiflexion, knee flexion, and hip flexion angles during the eccentric phase of CMJ were calculated. Repeated-measures ANOVA were used to identify significant differences in DSI, CMJ JH, mRSI, CMD, RPNI, and ankle dorsiflexion, knee flexion, and hip flexion angles between sex and across timepoints; pairwise comparisons were used for post hoc testing (p<.05, IBM SPSS, v.29). Results: A significant interaction between time and sex was found for DSI (p = .011), with females showing the highest DSI in the pre-season and males peaking in the early-season. Males consistently produced higher CMJ JH, mRSI, and IMTP peak forces than females (p < .001), but females demonstrated significantly higher overall DSI scores (p = .003). JH and mRSI significantly increased over time (p < .05), while CMD increased in females but decreased in males (p = .006). A significant time by sex interaction was also observed for delta hip flexion, with females exhibiting greater increases in flexion across the season. Conclusion: DSI and CMJ outputs evolve differently between sexes across a basketball season. Female athletes adopted a jump strategy with increased hip flexion and CMD, potentially as an adaptation to cumulative fatigue or load. These findings highlight the importance of sex-specific monitoring and suggest that incorporating DSI and kinematic analysis can guide training prescriptions for female and male basketball athletes to optimize performance.