Mechanomyographic and electromyographic responses during submaximal cycle ergometry

Abstract

The purpose of this study was to examine the mechanomyographic (MMG) and electromyographic (EMG) responses during continuous, cycle ergometer workbouts performed at constant power outputs. Eight adults [mean (SD) age, 21.5 (1.6) years] volunteered to perform an incremental test to exhaustion for the determination of peak power (Wpeak) and four, 15-min (or to exhaustion) rides at constant power outputs of 50%, 65%, 80%, and 95% Wpeak. Piezoelectric crystal contact sensors were placed on the vastus lateralis (VL) and vastus medialis (VM) muscles to record the MMG signals. Bipolar surface electrode arrangements were placed on the VL and VM to record the EMG signals. Five-second samples of the MMG and EMG signals were recorded every 30 s at power outputs of 50%, 65%, and 80% Wpeak, and every 15 s at 95% Wpeak. The amplitudes of the selected portions of the signals were normalized to the first values recorded during the continuous rides, and regression analyses were used to determine whether the slope coefficients for the MMG and EMG versus time relationships were significantly (P < 0.05) different from zero. The results indicate that EMG amplitude increased (range of slope coefficients: 0.03-0.56) during the continuous rides for both muscles at all four power outputs (except the VM at 50% Wpeak), while MMG amplitude increased (slope coefficient at 95% Wpeak for VM = 0.19), decreased (range of slope coefficients for VL and VM at 50% and 65% Wpeak = -0.14 to -0.24), or remained unchanged (range of slope coefficients for VL and VM at 80% Wpeak and VL at 95% peak = -0.06 to 0.12) depending on the power output. The patterns of the MMG responses, however, were similar for the VL and VM muscles, except at 95% Wpeak. Fatigue-induced changes in motor-unit recruitment and discharge rates, or muscular compliance may explain the differences between power outputs in the patterns of the MMG amplitude responses.

Shear elastic modulus can be used to estimate an index of individual muscle force during a submaximal isometric fatiguing contraction

“…6), EMG-RMS and force (indirectly assessed by shear elastic modulus herein) changed in similar ways. In other words, an increase in EMG activity level during a submaximal constant-load fatiguing exercise cannot be interpreted only as a sign of neuromuscular fatigue (20,32), because it can also indicate an increase in muscle force to compensate for fatigue in other muscles, i.e., change in muscle coordination (22). Other studies are necessary to further understand the high interindividual variability reported for change in shear elastic modulus, i.e., variability in muscle coordination during fatigue.…”

Physiological Responses Underlying the Perception of Effort during Moderate and Heavy Intensity Cycle Ergometry

“…A number of studies have examined the physiological and perceptual responses during continuous, constant PO cycle ergometry [1,2,4,5] within both moderate and heavy exercise intensity domains. During fatiguing constant PO exercise there are predictable time-dependent patterns of responses for O2, HR, rating of perceived exertion (RPE), breathing frequency ( ), and minute ventilation ( ) that are, in part, dependent upon the exercise intensity associated with the task.…”

Avaliação do sinal eletromiográfico como parâmetro para determinação do limiar de fadiga muscular

“…(PRINGLE e JONES, 2002;HOUSH, et al 2000;PAVLAT et al, 1995, 1993. MORITANI et al, 1993 (EBERSOLE, et al, 2005(EBERSOLE, et al, , 1999KOMI e TESCH, 1979).…”

“…Tomando-se por base a análise conjunta, e preliminar, dos tempos de exaustão em cada teste de fadiga e de seus (WEIR et. al., 2006;DEDERING et al, 2002;BORG, 1990 HOUSH et al, 2000HOUSH et al, , 1995PAVLAT et al, 1995PAVLAT et al, , 1993MORITTANI et al, 1993;deVRIES et al, 1990). …”