Muscle conduction velocity, surface electromyography variables, and echo intensity during concentric and eccentric fatigue

Abstract

The effects of the muscle damage produced by ECC exercise on the transmission of action potentials along muscle fibers (measured as the CV) may be comparable with the effects of hydrogen accumulation produced by CON exercise (related to greater lactate concentrations), which causes greater force loss and change in other sEMG variables during CON than during ECC actions.

Early resistance training-induced increases in muscle cross-sectional area are concomitant with edema-induced muscle swelling

“…The increase in CSA-US echo at T2 is somewhat expected, as strenuous exercises induce transient muscle edema during and following exercise (Fleckenstein et al 1988), especially in an early phase of the RT program when there is a greater probability of muscle damage (Chen et al 2009(Chen et al , 2013Nosaka and Sakamoto 2001). We report values around 61.5 AU (increase of ~17.2 %) at T2 (3 days after the last training bout) and previous work reported 62.7 AU for a typical participant and mean increases of ~15-20 % 2-3 days after a damaging bout of exercise (Chen and Nosaka 2006;Chen et al 2012Chen et al , 2013Gonzalez-Izal et al 2014). This evidence strengthens, we propose, the argument that some degree of muscle damage existed at T2.…”

“…This results in a histogram of grayscale shades (0: black, 256: white), where any abnormalities-such as edema-induced muscle swelling, probably due to muscle damage-result in higher US echo value (high echogenicity-increased white areas), while normal muscle mass has low echogenicity (less white areas). This method has been used extensively in the evaluation of exercise-induced changes in muscle quality and is indicative of edema and damage (Rosenberg et al 2014;Chen et al 2009Chen et al , 2012Chen et al , 2013Nosaka and Sakamoto 2001;Chen and Nosaka 2006;Gonzalez-Izal et al 2014). The same experienced investigator collected all images and conducted all analyses, which took place in a blinded manner.…”

“…For example, an increase in muscle US echo was found concomitantly with several markers of muscle damage such as decreased maximum voluntary isometric contraction torque (MVC) and range of motion, and increased muscle soreness and muscle protein leakage to blood stream (Nosaka and Sakamoto 2001;Chen et al 2012Chen et al , 2013Gonzalez-Izal et al 2014;Chen and Nosaka 2006). Moreover, an increase in muscle US echo concomitant with an increase in muscle size has been shown to be indicative of the presence of edemainduced muscle swelling (Nosaka and Sakamoto 2001;Chen et al 2012Chen et al , 2013Gonzalez-Izal et al 2014;Chen and Nosaka 2006). Therefore, an interesting approach to analyze if measurable increases in muscle CSA are mostly hypertrophy or are predominantly indicative of a swollen muscle is to normalize the magnitude of increase in muscle US echo by the increase in the respective muscle CSA during a period of RT.…”

Alterations in peak torque occur without hematological changes after muscle fatigue

“…Differences between muscle actions have already been investigated in the literature [16][17][18][19][20][21] demonstrating greater impairment in concentric muscle activation 3,19,20 , increased metabolic burden evaluated by lactate concentration 3 in concentric muscle actions and of elastic components specifically in the titin protein 16,21 have been recognized as indicators of this difference.…”

“…Studies 2 investigating muscle fatigue have been published that consider the multiple facets of the associated fatigue mechanisms, with a view to understanding the fatigue process. Some of the mechanisms involved in the fatigue process 2 , include changes in electromyography 3 , mechanical alterations 4 , changes in blood biochemistry 5 have received much attention. However, research related to hematological change is still inconclusive 6 .…”