Influences of sex and time interval on reliability of neuromuscular and motor performance measurements in isometric plantar flexor exercise

Purpose Reliable assessment of neuromuscular function is fundamental for interpreting physiological adaptations, yet sex-related influences in the reliability of these assessments remain poorly characterized across different temporal designs. We determined the within-session and between-days reliability of neuromuscular measurements in physically active men and women across multiple time intervals. Methods Thirty healthy participants (15♀ and 15 ♂) completed six sessions to assess the reliability of motor output such as maximal voluntary contraction and time-to-task failure during isometric plantar flexion, as well as electrically evoked responses such as H-reflex, M-wave and V-wave. Relative and absolute reliability were calculated in pooled and sex-separated data. Results Maximal voluntary contraction showed excellent within-session reliability in all groups. This outcome was consistently good in pooled data and in men for between-days sessions, yet only moderate in women. Although acceptable, within-session and between-days reliability of time-to-task failure were more variable in pooled and sex-separated data. Reliability of H-reflex, M-wave and V-wave ranged from good to excellent in within-session data for both sexes. However, between-days reliability was more variable, as men showed a higher reliability in H-reflex whereas women showed a higher reliability in M-wave and V-wave. Apparently, reliability of electrically evoked reflexes was influenced by the interval between measurements in women. Conclusion Maximal voluntary contraction is a reliable outcome to reflect adaptations in plantar flexion-derived motor output regardless of sex and temporal designs. Results suggested that sex-related influences affect the reliability of electrically evoked reflexes, challenging their ability to reflect biological adaptation of neuromuscular function.