Dynamic Strength Index in Basketball Players: Age and Position Differences, Seasonal Variation and Association with Sprinting and Change of Direction Performance

The aim of the study was to investigate the differences in bilateral and unilateral dynamic strength index (DSI) between age categories (seniors and juniors), player positions (guards and forwards), its variation during the basketball season, and its association with sprint and change of direction (CoD) performance. Highly trained basketball players (n = 32) performed bilateral and unilateral countermovement jumps (CMJ), bilateral and unilateral isometric squats, 10-m sprint, and 505 CoD test. DSI was calculated from CMJ and isometric peak force, while 10-m sprint and 505 test were used to calculate the CoD deficit. Two-way factorial analysis showed larger isometric peak force in seniors, and larger bilateral DSI in juniors, while guards had higher DSI values and larger peak force in both metrics compared to forwards. Two-way mixed model ANOVA showed a significant increase in unilateral isometric squat and CMJ peak force force (g =–0.08 to –0.64) and increase in bilateral DSI values. Post-hoc analysis showed that isometric squat force significantly increased only in seniors (g = 0.88), resulting in decreased bilateral DSI values (g = 0.52), with bilateral and unilateral DSI values increasing in juniors. Similar trends were observed in guards and forwards, with guards exhibiting a more pronounced increase in all variables compared to forwards. Furthermore, correlation analysis for in-season testing showed moderate associations between isometric squat peak force and CoD ability (r =–0.43 to –0.54; P < 0.001), and weak associations between DSI and CoD ability (r = 0.36 to 0.39; P < 0.05), while associations were not significant for sprint performance. The relationships were lower or absent during pre-season testing. Further interventional studies are needed to determine the usefulness of DSI to guide training related decision-making.