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

IntroductionFatigue effects on total relaxation delay (R-Delay(TOT)) components and measurement reliability were investigated. MethodsElectromyogram (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-t F-MMG), from the beginning to the end of MMG p-p (R-t MMG(p-p)), and from the end of MMG p-p to F cessation (R-t MMG-F-end) were calculated. ResultsR-Delay(TOT) lasted 36610 ms. R-EMD, R-t F-MMG, R-t MMG(p-p), and R-t MMG-F-end accounted for 6%, 8%, 59%, and 27% of R-Delay(TOT), respectively. After fatigue, R-Delay(TOT), R-EMD, R-t F-MMG, and R-t MMG(p-p) increased by 38%, 22%, 40%, 40%, and 38%, respectively (P<0.05). Reliability was very high (0.853-0.960). ConclusionsR-t MMG(p-p) was the main contributor to R-Delay(TOT). Fatigue affected all R-Delay(TOT) contributors, with a smaller effect on R-EMD. Muscle Nerve51: 907-915, 2015