Electromechanical delay components during relaxation after voluntary contraction: reliability and effects of fatigue

Introduction Fatigue effects on total relaxation delay (R-DelayTOT) components and measurement reliability were investigated. Methods Electromyogram (EMG), force (F), and mechanomyogram (MMG) were recorded during maximum voluntary contraction from the biceps brachii muscle before and after fatigue. The delays between EMG cessation and onset of F decay (R-EMD), between F decay and onset of MMG largest displacement (MMG p-p) (R-Δt F-MMG), from the beginning to the end of MMG p-p (R-Δt MMGp-p), and from the end of MMG p-p to F cessation (R-Δt MMG-Fend) were calculated. Results R-DelayTOT lasted 366 ± 10 ms. R-EMD, R-Δt F-MMG, R-Δt MMGp-p, and R-Δt MMG-Fend accounted for 6%, 8%, 59%, and 27% of R-DelayTOT, respectively. After fatigue, R-DelayTOT, R-EMD, R-Δt F-MMG, and R-Δt MMGp-p increased by 38%, 22%, 40%, 40%, and 38%, respectively (P