The study of a physiological index
Localised myoelectric fatigue is caused by the accumulation of lactates in the muscle that is sustaining work over a period of time.
This is a parameter that can be assessed in athletes, for the study of muscle function in preventive terms or in competitive conditions.
Different fatigue levels for different types of fibres
We studied how localised myoelectric fatigue spreads in knee extensor muscles in an elite football player (from the Italian Serie A). Surface electrodes were placed on the medial and lateral vastus and on the rectus femoris; the professional athlete performed an initial assessment at baseline through an isometric contraction, and then performed a tiring workout and repeated the test under conditions of increased muscle fatigue.
It can be clearly observed that, following strenuous exercise, the fibres that work at higher frequencies, i.e. the anaerobic white fibres, gradually fail. In contrast, the red resistance fibres, which usually work at frequencies below 100 Hz, remain active and still work.
More specifically, it was possible to differentiate the three heads of the quadriceps, observing that the two vastii lose more and more high frequency activations as the seconds pass during maximal contraction, in contrast to the rectus femoris, which accumulates less localised myoelectric fatigue even after some time.
The study of muscle physiology by means of surface electromyography can be an important tool for professional sports teams to build a correct preventive athletic preparation, starting from the initial evaluation at the beginning of the agonistics season; on the other hand, it can be a useful instrument for the rehabilitation team, which must encourage a safe return to athletic activity after an injury, minimising the risk of relapse.