The stability of variability - multiday reliability of sample entropy in submaximal hop and strength tasks in elite athletes

The purpose of this study was to determine the multiday reliability in submaximal continuous hops and submaximal isometric squats from the ground reaction force signals. Twelve elite team-sport athletes completed submaximal isometric squats at 40% and 60% of their maximal voluntary isometric contraction and submaximal continuous hopping at 2 Hz, 2.5 Hz, and a self-selected frequency for 30 s, respectively, over four sessions. Sample entropy was calculated from the force-time data. Good-to-excellent reliability (ICC_2,k > 0.75) was observed for submaximal hopping frequencies (Hop2.0, Hop2.5) following one session and for isometric squats at 60% MVIC from the initial session. These data suggest a stable force-time structure across testing days, indicating that sample entropy can detect meaningful changes for these tasks between testing days.