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 MMGp-p ) were calculated. Results: R-DelayTOT lasted 366±10 ms. R-EMD, R-Δt F-MMG, R-Δt MMGp-p , and R-Δt MMGp-p -F 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<0.05). Reliability was very high (0.853-0.960). Discussion: R-Δt MMGp-p was the main contributor to R-DelayTOT . Fatigue affected all R-DelayTOT contributors, with a smaller effect on R-EMD.