Evaluation of performance fatigability through surface EMG in health and muscle disease: state of the art

Abstract

In literature, it is commonly reported that the progress of performance fatigability may be indirectly assessed through the changes in the features of the surface electromyogram (sEMG) signal. In particular, during isometric constant force contractions, changes in the sEMG signal are caused by several physiological factors, such as a decay in muscle fibers conduction velocity (CV), an increase of the degree of synchronization between the firing times of simultaneously active motor units (MUs), by the central nervous system, and a reduction of the recruitment threshold and a modulation of MUs firing rate. Amplitude and spectral parameters may be used to characterize the global contributions to performance fatigability, such as MU control properties and fiber membrane properties, or central and peripheral factors, respectively. In addition, being CV a physiological parameter, its estimation is of marked interest to the study of fatigue both in physiological and in presence of neuromuscular diseases.

Effects of a Single Dose of a Creatine-Based Multi-Ingredient Pre-workout Supplement Compared to Creatine Alone on Performance Fatigability After Resistance Exercise: A Double-Blind Crossover Design Study

“…FD is the slope of the interpolation line (as determined by the least mean squared method). Performance fatigability was indirectly calculated as the slopes (% of rate of change) of the considered sEMG variables (CV and FD) ( 14 ).…”

“…According to Enoka and Duchateau (13), performance fatigability is typically quantified as the decline in an objective measure of performance over a discrete period, while perceived fatigability refers to changes in the sensations that regulate the integrity of the performer. Many factors interact and contribute to performance fatigability (14)(15)(16). These factors may be classified as central or peripheral.…”

“…In particular, during isometric tasks, fatigue-related changes in the sEMG signal are linked to several physiological factors, such as a decay in muscle fiber conduction velocity (CV) of motor unit action potentials (MUAPs), an increase in the degree of synchronization between the firing times of simultaneous MUs (by the central nervous system), and a reduction of the recruitment threshold of MUs firing rate (21). Therefore, to assess peripheral and central components of performance fatigability, rates of change (i.e., slope) of CV (21)(22)(23), and fractal dimension (FD) of the sEMG signal, which is highly reliable on MUs synchronization (14,24,25), might be measured during isometric muscle tasks, respectively.…”

“…In contrast, peripheral factors, which impair the execution of the descending central commands ( 17 ), include local changes at the skeletal muscle level that occur during prolonged activity, such as glycogen depletion, impaired regulation of calcium ions (Ca 2+ ) flux in the cell matrix ( 18 ), reduction of intramuscular adenosine triphosphate (ATP) and creatine level ( 19 ), elevated concentrations of inorganic phosphate (P i ), and excess of hydrogen ions (H + ) ( 20 ). Even though no gold standard to assess performance fatigability is currently recognized, changes in the myoelectric activity of a selected muscle by surface electromyography (sEMG) may be used to indirectly assess performance fatigability ( 14 ). In particular, during isometric tasks, fatigue-related changes in the sEMG signal are linked to several physiological factors, such as a decay in muscle fiber conduction velocity (CV) of motor unit action potentials (MUAPs), an increase in the degree of synchronization between the firing times of simultaneous MUs (by the central nervous system), and a reduction of the recruitment threshold of MUs firing rate ( 21 ).…”