Running Head: Modulation of corticospinal excitability during arm cycling

44 45 Human studies have not assessed corticospinal excitability of an upper-limb prime mover 46 during arm cycling. The purpose of the present study was to determine whether supraspinal 47 and/or spinal motoneurone excitability of the biceps brachii was different between arm cycling 48 and an intensity-matched tonic contraction. We hypothesized that spinal motoneurone 49 excitability would be higher during arm cycling than an intensity-matched tonic contraction. 50 Supraspinal and spinal motoneurone excitability were assessed using transcranial magnetic 51 stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of the 52 corticospinal tract, respectively. TMS-induced motor evoked potentials (MEPs) and TMES53 induced cervicomedullary evoked potentials (CMEPs) were assessed at three separate positions 54 (3, 6 and 12 o’clock relative to a clock face) during arm cycling and an intensity-matched tonic 55 contraction. MEP amplitudes were 7.2 and 8.8% Mmax larger during arm cycling when compared 56 to a tonic contraction at the 3 (P < 0.001) and 6 o’clock (P < 0.001) positions, respectively. 57 There was no difference between tasks during elbow extension (12 o’clock). CMEP amplitudes 58 were 5.2% Mmax larger during arm cycling when compared to a tonic contraction at the 3 o’clock 59 position (P < 0.001) with no differences seen at mid-flexion (6 o’clock) or extension (12 60 o’clock). The data indicate an increase in the excitability of corticospinal neurones which 61 ultimately project to biceps brachii during the elbow flexion portion of arm cycling and increased 62 spinal motoneurone excitability at the onset of elbow flexion during arm cycling. We conclude 63 that supraspinal and spinal motoneurone excitability are phaseand task-dependent. 64