Effects of leg pedaling on early latency cutaneous reflexes in upper 2 limb muscles

31 The functional coupling of neural circuits between the upper and lower 32 limbs involving rhythmic movements is of interest to both motor control 33 research and rehabilitation science. This coupling can be detected by 34 examining the effect of remote rhythmic limb movement on the modulation 35 of reflex amplitude in stationary limbs. The present study investigated the 36 extent to which rhythmic leg pedaling modulates the amplitude of an early 37 latency (peak 30–70 ms) cutaneous reflex (ELCR) in the upper limb muscles. 38 Thirteen neurologically intact volunteers performed leg pedaling (60 or 90 39 rpm) while simultaneously contracting their arm muscles isometrically. 40 Control experiments included isolated isometric contractions and discrete 41 movements of the leg. ELCRs were evoked by stimulation of the superficial 42 radial nerve with a train of rectangular pulses (3 pulses at 333 Hz, intensity 43 2–2.5× perceptual threshold). Reflex amplitudes were significantly increased 44 in the flexor carpi radialis (FCR) and posterior deltoid (PD), and significantly 45 decreased in the biceps brachii (BB) muscles during leg pedaling compared to 46 during stationary isometric contraction of the lower leg muscles. This effect 47 was also sensitive to cadence. No significant modulation was seen during the 48 isometric contractions or discrete movements of the leg. Additionally, there 49 was no phase-dependent modulation of the ELCR. These findings suggest 50