Changes in corticospinal excitability and motoneurones responsiveness during and within a time-course after submaximal fatiguing contractions

The objective of the present study was to investigate the changes in corticospinal excitability and motoneurones responsiveness of Biceps Brachii muscle during and within a time-course after submaximal fatiguing contractions. Eight active male (Age 29.6 ± 1.92 yrs., Height 181 ± 3.46 cm, Weight 78.3 ± 4.74) volunteered to take part in this study and reported to the laboratory on three different occasions. After measuring 1RM and familiarization with the experimental procedure in the session one, in the second and third visits, motor evoked potential (MEP) and cervicomedullary motor evoked potential (CMEP) were assessed immediately after each bout and 5-minute and 10-minute after the termination of the task by the use of magnetic stimulation over the motor cortex and spinal routes respectively. Three bouts of 3-minute (T1,T2,T3) elbow flexion and extension at 25% of 1RM separated by a 1-minute rest were used as the fatiguing task. Our results by the use of one-way repeated measures ANOVA showed a significant decrease in MEP after T2 (P₌0.006), T3 (P₌0.006), and after 5-minute (P₌0.000), during the recovery time. The results also indicated CMEP to significantly decline after T1 (P₌0.014), T2 (P₌0.008), and T3 (P₌0.010). It seems that both spinal and supraspinal mechanisms contribute to performance reduction in the submaximal fatigue. Moreover, it takes the CNS a longer time to recover from fatigue induced by submaximal contractions.