Muscle contraction type does not influence the etiology of the immediate crossover fatigue evidenced after submaximal unilateral exercises of knee flexor muscles

Motor performance fatigue can occur in a non-exercised muscle following a unilateral exercise performed with the contralateral homologous muscle. While many studies have investigated this crossover fatigue phenomenon, the influence of muscle contraction type is unsettled. This study examined the occurrence and etiology of crossover fatigue after submaximal isometric (ISO), concentric (CONC) or eccentric (ECC) contractions of the knee flexors (KF). In separate sessions, thirteen participants performed unilateral ISO, CONC or ECC KF exercises inducing a 20 % reduction in maximal voluntary isometric contraction (MVIC) of the exercised limb (EL). Motor performance fatigue (i.e., MVIC, voluntary activation [VA], electrically evoked muscle responses [Pt 100Hz and Pt 10Hz -to-Pt 100Hz ratio]) and perceived muscle soreness (PMS) of both EL and nonexercised limb (NEL) were assessed before (PRE), immediately (POST), and 24 h post-exercise (POST24). Global perceived motor fatigue (PMF) was also measured. At POST, significant reductions in MVIC were observed for both EL (-27.7 %; p < 0.001) and NEL (-8.5 %; p < 0.01) indicating the presence of crossover fatigue. At POST, Pt 100Hz (-7.5 %; p < 0.05) was impaired in both limbs whereas VA was altered in the EL only (-2.6 %; p < 0.001). PMF was increased at POST only (p < 0.001). Finally, PMS scores were greater at POST (p < 0.01) and POST24 (p < 0.001) than PRE values regardless of the limb considered. At POST24, MVIC, Pt 100Hz , VA and PMF had returned to PRE values. Muscle contraction type did not influence crossover fatigue of the KF nor its etiology.