Corticospinal excitability is higher during synchronous vs asynchronous arm cycling.

This is the first study to assess corticospinal excitability during synchronous and asynchronous arm cycling modes. Corticospinal excitability to the biceps and triceps brachii was assessed using transcranial magnetic stimulation (TMS) of the motor cortex. Motor evoked potentials (MEPs) were evoked during the mid-flexion position of arm cycling across two modes; (1) synchronous (Sync) and (2) asynchronous (Async) cycling at three different cadences; 30, 60 and 90rpm. The power output was kept constant at 30watts throughout the cycling trials. In the biceps brachii muscle, TMS-induced motor evoked potential (MEP) amplitudes were significantly higher during the synchronous mode compared to the asynchronous arm cycling mode (F(1,10) = 12.18, p < 0.05). However, MEP amplitudes were not significantly different between both modes in the triceps brachii muscle at the mid elbow flexion phase of arm cycling. There was also no significant difference in the corticospinal excitability to both muscles between the two modes as the cycling cadence increased from 30 to 90rpm (i.e. no interaction effect between mode and cadence). In line with our previous studies, we observed that MEP amplitudes increased as the cycling cadence increased from 30 to 90rpm in both the biceps brachii (F(2,20) = 12.92, p < 0.01) and triceps brachii (F(2,20) = 6.314, p < 0.05). We suggest that the observed higher corticospinal excitability observed during Sync mode in the biceps brachii might be due to increased interhemispheric facilitation (cortical spread) and/or reduced interhemispheric inhibition at the cortical level.