Surface Electromyography Amplitude During Sustained Isometric Contractions
Connor Howe
31451131
HMKN 310
UBC Okanagan
Greg duManoir
October 18, 2015
Introduction
Muscle fatigue is the result of a series of structural, metabolic and energetic changes in muscle fibers caused by changes in nervous system efficiency as well as decreased oxygen and nutrient supply (Cifrek, Medved, Tonković, & Ostojić, 2009). A major driving force behind muscle fatigue is lactate buildup. As lactate builds up there is a shift in intracellular pH levels which causes a change in the waveform shape of the motor unit action potential. This causes a decrease in the conduction velocity of the muscle fiber. (Cifrek et al., 2009).
Methods in measuring muscle fatigue vary and include surface electromyography (sEMG), measuring blood lactate, and by observing the point of force decrease when performing a maximum isometric contraction (Cifrek et al., 2009). In this lab sEMG is chosen for measurement of fatigue as it is non-invasive and can provide continuous monitoring during contraction compared to lactate monitoring which requires the subject to be stationary and does not allow continuous …show more content…
The 100% sustained maximal contraction was the only trial where S-EMG amplitude was lower in the final 5 second time interval compared to the first time interval (figure 5). During the submaximal isometric handgrip contraction where subjects performed 25% and 50% of their maximum voluntary contraction the sEMG amplitude increased by 10.5% (figure 2) and by 52.6% (Figure 3) while the increase during the 75% contraction only increased by 4.2% (figure 4). The large increase in amplitude during the 50% MVC is due to a combination of increased motor unit firing frequency and increase number of motor units firing to offset the effects of fatigue (Moritani, Muro, & Nagata,
Connor Howe
31451131
HMKN 310
UBC Okanagan
Greg duManoir
October 18, 2015
Introduction
Muscle fatigue is the result of a series of structural, metabolic and energetic changes in muscle fibers caused by changes in nervous system efficiency as well as decreased oxygen and nutrient supply (Cifrek, Medved, Tonković, & Ostojić, 2009). A major driving force behind muscle fatigue is lactate buildup. As lactate builds up there is a shift in intracellular pH levels which causes a change in the waveform shape of the motor unit action potential. This causes a decrease in the conduction velocity of the muscle fiber. (Cifrek et al., 2009).
Methods in measuring muscle fatigue vary and include surface electromyography (sEMG), measuring blood lactate, and by observing the point of force decrease when performing a maximum isometric contraction (Cifrek et al., 2009). In this lab sEMG is chosen for measurement of fatigue as it is non-invasive and can provide continuous monitoring during contraction compared to lactate monitoring which requires the subject to be stationary and does not allow continuous …show more content…
The 100% sustained maximal contraction was the only trial where S-EMG amplitude was lower in the final 5 second time interval compared to the first time interval (figure 5). During the submaximal isometric handgrip contraction where subjects performed 25% and 50% of their maximum voluntary contraction the sEMG amplitude increased by 10.5% (figure 2) and by 52.6% (Figure 3) while the increase during the 75% contraction only increased by 4.2% (figure 4). The large increase in amplitude during the 50% MVC is due to a combination of increased motor unit firing frequency and increase number of motor units firing to offset the effects of fatigue (Moritani, Muro, & Nagata,