Between Session Reliability Of Traditional And Temporal Bilateral And Unilateral Dynamic Strength Index Calculations And Association With Sprint And Change Of Direction Performance

Tallis, J, Bolt, L, Morris, OR, Suchomel, TJ, and Eustace, SJ. Between session reliability of traditional and temporal bilateral and unilateral dynamic strength index calculations and association with sprint and change of direction performance. J Strength Cond Res XX(X): 000–000, 2025—The present study aimed to (a) evaluate the between session reliability of traditional and temporal based bilateral and unilateral dynamic strength index (DSI); (b) determine the association between DSI and sprint and change of direction performance in participants clustered by DSI root metrics. Thirty-eight recreationally active male participants (age: 23.4 ± 3.4 years) completed 20-m sprints, 5-0-5 change of direction test, bilateral and unilateral countermovement jumps (CMJ), and isometric midthigh pulls (IMTP) on 2 occasions. Vertical ground reaction force profiles were assessed to determine traditional DSI (DSIT), DSI based on mean force achieved after 100 milliseconds (DSI100), 150 milliseconds (DSI150), the entire CMJ propulsive phase (DSIP), and CMJ propulsive impulse (DSII). Bayesian interclass correlation coefficients and multiple linear regression after K-means clustering were used to analyze the data. Between session reliability of DSI was poor-moderate (interclass correlation coefficient [ICC] = 0.24–0.76) and highest for DSIT measures, albeit with some uncertainty (95% Higher Density Intervals [HDI]: 0.53–0.87). Bilateral temporal based DSI reliability was greater compared with unliteral equivalents, and temporal based DSI calculated for the nondominant limb, and those determined over a small-time epoch for the dominant limb were poor. There was limited association across DSI measures and straight-line 20-m sprint and 5-0-5 change of direction performance test. DSI100 for the dominant side had the strongest association with the performance outcomes (R2 = 0.33–0.36) and was improved in participants that expressed higher CMJ peak propulsive force. Dynamic strength index should be used with caution with respect to exercise prescription for the intention of improving tasks requiring rapid horizontal center of mass translation.