Effects of Leg Pedaling on Early Latency Cutaneous Reflexes in Upper Limb Muscles

Abstract

The functional coupling of neural circuits between the upper and lower limbs involving rhythmic movements is of interest to both motor control research and rehabilitation science. This coupling can be detected by examining the effect of remote rhythmic limb movement on the modulation of reflex amplitude in stationary limbs. The present study investigated the extent to which rhythmic leg pedaling modulates the amplitude of an early latency (peak 30-70 ms) cutaneous reflex (ELCR) in the upper limb muscles. Thirteen neurologically intact volunteers performed leg pedaling (60 or 90 rpm) while simultaneously contracting their arm muscles isometrically. Control experiments included isolated isometric contractions and discrete movements of the leg. ELCRs were evoked by stimulation of the superficial radial nerve with a train of rectangular pulses (three pulses at 333 Hz, intensity 2.0- to 2.5-fold perceptual threshold). Reflex amplitudes were significantly increased in the flexor carpi radialis and posterior deltoid and significantly decreased in the biceps brachii muscles during leg pedaling compared with that during stationary isometric contraction of the lower leg muscles. This effect was also sensitive to cadence. No significant modulation was seen during the isometric contractions or discrete movements of the leg. Additionally, there was no phase-dependent modulation of the ELCR. These findings suggest that activation of the rhythm generating system of the legs affects the excitability of the early latency cutaneous reflex pathways in the upper limbs.

Robotic-assisted stepping modulates monosynaptic reflexes in forearm muscles in the human

“…Probably descending commands accompanying active arm cycling generate phasic modulation of the H-reflex during remote rhythmic movement. Based on these and our findings, it is likely that afferent information for stepping plays an important role in generating tonic suppression of the H-reflex amplitude in remote muscles Sasada et al 2010). These features of the general suppression of forelimb reflex excitability during passive leg stepping can be explained by the afferent-induced presynaptic inhibition on the Ia terminals of the FCR H-reflex circuitry during locomotor activity Frigon et al 2004;Misiaszek et al 1998;Sasada et al 2010;Zehr and Duysens 2004).…”

“…Based on these and our findings, it is likely that afferent information for stepping plays an important role in generating tonic suppression of the H-reflex amplitude in remote muscles Sasada et al 2010). These features of the general suppression of forelimb reflex excitability during passive leg stepping can be explained by the afferent-induced presynaptic inhibition on the Ia terminals of the FCR H-reflex circuitry during locomotor activity Frigon et al 2004;Misiaszek et al 1998;Sasada et al 2010;Zehr and Duysens 2004). This discussion is based on indirect evidence in humans (Frigon et al 2004;Zehr et al 2007), and further study is needed to determine the possible contribution of presynaptic inhibition on suppression of the H-reflex pathway during passive movement of the remote limb.…”

Reflex modulation during rhythmic limb movements in humans

“…If possible, changes in load using counter weights, water immersion, and changes in axial resistance load can be used to investigate the nature of the CPG system in humans 6,7,61,63) .…”

“…Thus, during rhythmic arm and leg movement, significant changes in the reflex effect in given limb muscles can be easily masked by phase modulation coming from the intralimb effect. Recently, we examined to what extent the excitability of the early latency cutaneous reflexes (ELCR, peak latency ~30-70 ms) in the stationary arm muscles are modulated during different types of rhythmic leg cycling 63) . The subjects performed leg pedaling (60 or 90 rpm) while simultaneously contracting their arm muscles isometrically.…”

“…In addition, these findings further support the contribution of an interlimb interaction between the presumed lower limb neural system and the neural circuit of the cutaneous reflex in the upper limbs 6,8,21,94) . This would result in an increase of the excitability of the circuitry for the cutaneous reflex (offset regulation) 63) . .…”