Evaluation of central and peripheral myoelectric manifestations of fatigue using fractal dimension and conduction velocity: a feasibility study

Beretta Piccoli, Matteo and D'Antona, Giuseppe and Clijsen, Ron and Cescon, Corrado and Barbero, Marco (2014) Evaluation of central and peripheral myoelectric manifestations of fatigue using fractal dimension and conduction velocity: a feasibility study. In: Swiss Congress for Health Professions, March 11th-12th, 2014, Bern.

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Hintergrund/Einleitung Over the past decade several new sEMG descriptors for central fatigue have been developed and tested in simulation studies or in healthy subjects. Mesin and colleagues (2009) proposed a novel vector composed of two indexes, (1) estimated CV (conduction velocity) as indicator of peripheral fatigue and (2) FD (fractal dimension) as indicator of central fatigue. FD is a promising index, least affected by muscle fiber CV changes and mostly related to motor unit synchronization, although FD was never tested during a fatiguing task in healthy subjects, nor in patients. Ziel, Fragestellung To assess if the fatigue vector (CV, FD) is able to highlight different strategies of adaptation to central and peripheral fatigue in power and endurance athletes. Methode, Ergebnisse Two healthy female athletes participated in the study after providing informed consent: a power athlete, whose specialty was javelin throw and 100 and 200 meters run and an endurance athlete, whose specialty was marathon and triathlon. Myoelectric signals were detected fromthe muscles vastus lateralis and vastus medialis in single differential configuration using bi-dimensional arrays. FD and CV were measured by surface electromyography (sEMG) during a low level isometric contraction (20% MVC) for one minute, in order to allow an evaluation of peripheral fatigue of type I muscle fibers, followed by an endurance isometric contraction (60% MVC) until exhaustion, in order to evaluate peripheral fatigue of type II muscle fibers. The slope of CV during the 60% MVC is much more negative in the endurance athelete both in the VL and VM muscles, whereas the slope of FD during the same exercise is much more negative in the power athelete. Schlußfolgerungen, Diskussion The behavior of CV and FD of the two elite athletes reflects the differences in the adaptation of the central nervous system to fatigue. The 20% MVC contraction was not fatiguing for either the two athletes, while the 60% MVC contraction was fatiguing but in different ways. The endurance athlete showed more peripheral fatigue while the power athlete had almost no change of CV during the 60% contractions while the FD was decreasing for the power athlete, which indicates an increase of motor unit synchronization, thus suggesting central fatigue. This study demonstrated that the bi-dimensional index (CV, FD) is an effective indicator of central and peripheral muscle fatigue, that could be used to evaluate neuromuscular adaptations to fatigue in sport sciences.

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