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

Abstract

To investigate the within- and between-session reliability of the isometric mid-thigh pull (IMTP) in pre- and post-peak height velocity (PHV) female athletes. Nineteen pre- and nineteen post-PHV athletes performed bilateral IMTPs using a custom-designed isometric testing system. Participants attended three separate testing-sessions, and performed three trials within each session. Peak force, relative peak force, force at 30, 50, 90, 100, 150, 200, and 250 milliseconds, rate of force development (RFD) within time-specific bands, time to peak force (TPF), and time to peak rate of force development (TPRFD) were obtained for analysis. Within- and between-session reliability for each variable were calculated from repeated-measures analysis of variance, intraclass correlation coefficients (ICC), 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.