Understanding corticospinal excitability to the biceps brachii during maximal repeated arm-cycling sprints

Abstract

Studies investigating neuromuscular fatigue (NMF) induced by repeated sprint exercise primarily use a tonic contraction to assess corticospinal excitability (CSE). There is a lack of information about how CSE transiently changes with rapidly changing fatigue levels. Previous research has shown that CSE is dependent on a variety of factors, such as the targeted muscle, mode of exercise, hand position, cadence, cycling direction, and level of fatigue. No study has assessed CSE during repeated maximal arm-cycling sprints. The current study circumvents the limitations of a tonic contraction to assess CSE. We performed maximal repeated arm-cycling sprints using a custom-built cycle ergometer. Transcranial magnetic stimulation (TMS), transmastoid electrical stimulation (TMES), and brachial plexus stimulation (Erb’s point) were given during each sprint to determine how CSE to the biceps brachii was modulated during 5, approximately 20 second repeated sprints. The sprint protocol induced NMF as evidenced by mean power (p < 0.0001) and total work (p < 0.0001) dropping by 36.8% from sprint one to five respectively. There was a 4.57% decrease in TMES intensity required for the active motor threshold (AMT) from pre- (134.00 ± 31.52 mA) to post sprinting (124.17 ± 30.08 mA), t (12) = 3.445, p = 0.0055. Our findings suggest that our protocol increased spinal and peripheral excitability from pre to post sprinting, but not cortical because of the absence in change in MEP amplitudes from pre to post sprinting Changes at the spinal motoneuron and post-activation potentiation are likely mechanisms associated with the modulations.