Reproducibility of peak force for isometric and isokinetic multi-joint leg extension exercise

BACKGROUND: Isokinetic dynamometry is a common tool for evaluating muscle function and is used across various disciplines. Technical advancements have shifted focus towards multi-joint exercises such as the leg press, offering insights into practical human movement dynamics. However, previous reproducibility studies have focused predominantly on single-joint exercises, warranting investigations into the reliability of multi-joint exercises. This study aimed to assess the reproducibility of peak force (PF) during multi-joint leg press exercises using the IsoMed 2000 dynamometer.

METHODS: Thirty physically active subjects (mean: stature 179.4 cm; body mass 76.0 kg; age 30.6 years) participated in three testing sessions. Each session consisted of isometric and isokinetic leg press exercises. Knee angles for isometric exercises included 100° and 140°; velocities for isokinetic exercise included 30 mm/s and 600 mm/s. The first session served as the familiarization session. Statistical analysis included paired sample t-tests, Cohen's d effect sizes, intraclass correlation coefficients (ICC), standard errors of measurement (SEM), and Bland-Altman calculations, including corresponding plots.

RESULTS: Descriptive data revealed consistent PF across sessions, with a significant between-sessions difference observed only for isometric (100°) leg extension in the right leg (p < 0.001; d = 0.13). ICC calculations showed high relative reproducibility (ICC > 0.911), with SEM ranging from 37.6 to 294.7 N (SEM% 2.3-6.3%, respectively). Bland-Altman plots depicted minimal intersession disparities (-141.8-68.3 N, respectively - 3.02-1.26%), supporting high reliability.

CONCLUSIONS: This study highlights the reliability of assessing peak force during isometric and isokinetic leg press exercises using the IsoMed 2000 after a single familiarization session. These findings support its utility in muscular performance evaluation, urging practitioners to incorporate familiarization trials for accurate assessments.