Biceps brachii muscle fatigue during isometric contraction: is antagonist muscle fatigue a key factor?

Abstract: Purpose: Several studies analyzed muscle activity after pre-fatigue due to co-contraction, but the effects of antagonist contraction on agonist muscle performance are still incompletely known. The purpose is to determine if a previous workout of an antagonist muscle can affect muscular fatigue appearance during the subsequent agonist muscle performance. Methods: Surface EMG was used to estimate biceps brachii muscle fatigue during isometric contraction executed after previous contractions of the antagonist muscle. Eight expert male body-builders performed five series of isometric contractions (30 s) alternatively according to the agonist and antagonist protocols. Results: Within each repetition, for both biceps brachii muscles and experimental protocols, data showed a progressive fatigue, but no continuous quantitative decreasing trend of the median frequency of the spectrum along the five repetitions. Contraction time explained 1-91% (r2 values) of the reduction of mean activation frequency along the 30 s(agonistic protocol); 0.7-92% for antagonistic protocol. The decrement in median frequency was only partially time–related. A repeated measures Anova found significant differences between subjects (p<0.0001), protocols (antagonistic greater than agonistic, p=0.03), while between sides (p=0.93) and repetitions (p=0.50), and for all interactions no significant differences were found. Conclusion: The present results did not confirm that the antagonistic pre-fatiguing can delay the fatigue appearance during agonistic performance (isometric tasks). Accordingly, the antagonistic protocol does not seem to be functional in improving the upper arm performance from a fatigue point of view, at least in trained subjects.