Reliability and Sensitivity of Using Isometric Strength and Sprint Speed Measures in Adolescent Female Athletes

Salter, J, Forsdyke, D, Dawson, Z, Rymer, J, Walsh, L, and Mundy, P. Reliability and sensitivity of using isometric strength and sprint speed measures in adolescent female athletes. J Strength Cond Res XX(X): 000-000, 2024-The aim of this study was to establish the reliability and sensitivity of isometric mid-thigh pull (IMTP) and sprint speed (5 m, 40 m, and maximal sprint speed) in adolescent women, before exploring the stability of this across maturation to provide maturity-specific benchmarks. A total of 147 female athletes (age: 13.8 ± 2.8 years; stature: 157.1 ± 13.1 cm; body mass: 51.2 ± 15.3 kg; percentage of predicated adult height: 94.3 ± 6.6) performed IMTP and sprint trials on 2 occasions, separated by 7-days. Within- and between-session reliability was determined using intraclass correlation coefficient (ICC), coefficient of variation, and Bland-Altman limits of agreement, with sensitivity detected by signal-to-noise ratios for small (SWC0.2) and moderate (SWC0.5) worthwhile change. A between-group analysis of variance and Cohen's d-effect sizes determined differences between biological maturity groups (pre-, mid-, and post-peak height velocity [PHV]). All isometric strength and sprint performance markers demonstrated either "moderate" or "acceptable" within-session reliability, except for time to peak force (PF) and 40 m sprint. Despite metrics all having "high" or above ICC (0.55-0.98), only PF offered a "good" sensitivity when using SWC0.2, with most offering better sensitivity with SWC0.5. Noise was higher between sessions, resulting in "poor" signal-noise ratios, likely associated with the bias favoring retest trials. Reliability and sensitivity findings were consistent across maturational stages, demonstrating either "moderate" or "acceptable" reliability. There were clear differences between maturity groups for all measures, particularly between mid-PHV and post-PHV. Practitioners can be assured that IMTP and sprint performance measures are reliable within this population but require thorough familiarization processes before confidence in interpreting meaningful changes.