Intrasession and intersession reliability in maximal and explosive isometric torque production of the elbow flexors.

The purpose of this study was to assess intrasession and intersession reliability of maximal and explosive isometric torque production of the elbow flexors and its respective neuromuscular activation pattern. Subjects (13 men, age: 24.8 ± 3.1 years, height: 1.9 ± 0.1 m, body mass: 83.7 ± 12.7 kg; and 6 women, age: 26.5 ± 1.4 years, height: 1.7 ± 0.1 m, body mass: 62.7 ± 7.0 kg) were tested and retested 2-7 days later performing unilateral maximal isometric elbow flexions. Absolute (coefficient of variation [CV], test-retest variability [TRV], Bland-Altman plots with 95% limits of agreement) and relative reliability statistics (intraclass correlation coefficient) were calculated for various mechanical (i.e., maximal isometric torque, rate of torque development, impulse) and electromyographical measures (i.e., mean average voltage) at different time intervals relative to onset of torque (i.e., 30, 50, 100, 200, 300, 400, 100-200 ms). Intraclass correlation coefficient values were ≥ 0.61 for all mechanical and electromyographical measures and time intervals indicating good to excellent intrasession and intersession reliability. Bland-Altman plots confirmed these findings by showing that only 0-2 (≤ 13.3%) data points were beyond the limits of agreement. Regarding torque and electromyographic measures, CV (11.9-32.3%) and TRV (18.4-53.8%) values were high during the early intervals of torque development (≤ 100 ms) indicating high variability. During the later intervals (>100 ms), lower CV (i.e., 5.0-29.9%) and TRV values (i.e., 5.4-34.6%) were observed indicating lower variability. The present study revealed that neuromuscular performance during explosive torque production of the elbow flexors is reproducible in time intervals >100 ms after onset of isometric actions, whereas during earlier time intervals variability is high.