Within- and between-session reliability of the isometric midthigh pull in young female athletes

To investigate the within- and between-session reliability of the isometric midthigh pull (IMTP) in pre- and post-peak height velocity (PHV) female athletes. Nineteen pre- and 19 post-PHV athletes performed bilateral IMTPs using a custom-designed isometric testing system. Participants attended 3 separate testing sessions and performed 3 trials within each session. Peak force, relative peak force, force at 30, 50, 90, 100, 150, 200, and 250 ms, rate of force development (RFD) within time-specific bands, time to peak force (TPF), and time to peak RFD were obtained for analysis. Within- and between-session reliability for each variable was calculated from repeated-measures analysis of variance, intraclass correlation coefficients (ICCs), and coefficients of variation (CV) with 95% confidence intervals. Within-and between-session measures of absolute and relative peak force were found to be reliable for both pre-PHV (CV ≤ 9.4%, ICC ≥ 0.87) and post-PHV (CV ≤ 7.3%, ICC $ 0.92), but systematic bias was evident between sessions in the pre-PHV group, from session 1 to 2. Analyses of force at the specific time points revealed CVs between 19-37% and 5-24% for pre-PHV and post-PHV athletes, respectively. Greater variability was evident in TPF, and all RFD-related variables for pre-PHV (CV ≥ 38%) and post-PHV (CV ≥ 27%) athletes, respectively. The IMTP appears a reliable and safe method for evaluating peak force in young female athletes. Overall, post-PHV athletes were more reliable than pre-PHV athletes, with pre-PHV athletes needing additional familiarization to minimize the influence of systematic bias.