Effect of Rhythmic Arm Movement on Reflexes in the Legs: Modulation of Soleus H-Reflexes and Somatosensory Conditioning

Abstract

During locomotor tasks such as walking, running, and swimming, the arms move rhythmically with the legs. It has been suggested that connections between the cervical and lumbosacral spinal cord may mediate some of this interlimb coordination. However, it is unclear how these interlimb pathways modulate reflex excitability during movement. We hypothesized that rhythmic arm movement would alter the gain of reflex pathways in the stationary leg. Soleus H-reflexes recorded during arm cycling were compared with those recorded at similar positions with the arms stationary. Nerve stimulation was delivered with the right arm at approximately 70 degrees shoulder flexion or 10 degrees shoulder extension. H-reflexes were evoked alone (unconditioned) or with sural or common peroneal nerve (CP) conditioning to decrease or increase soleus IA presynaptic inhibition, respectively. Both conditioning stimuli were also delivered with no H-reflex stimulation. H-reflex amplitudes were compared at similar M-wave amplitudes and activation levels of the soleus. Arm cycling significantly reduced (P < 0.05) unconditioned soleus H-reflexes at shoulder flexion by 21.7% and at shoulder extension by 8.8% compared with static controls. The results demonstrate a task-dependent modulation of soleus H-reflexes between arm cycling and stationary trials. Sural nerve stimulation facilitated H-reflexes at shoulder extension but not at shoulder flexion during static and cycling trials. CP nerve stimulation significantly reduced H-reflex amplitude in all conditions. Reflexes in soleus when sural and CP nerve stimulation were delivered alone, were not different between cycling and static trials; thus the task-dependent change in H reflex amplitude was not due to changes in motoneuron excitability. Therefore modulation occurred at a pre-motoneuronal level, probably by presynaptic inhibition of the IA afferent volley. Results indicate that neural networks coupling the cervical and lumbosacral spinal cord in humans are activated during rhythmic arm movement. It is proposed that activation of these networks may assist in reflex linkages between the arms and legs during locomotor tasks.

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

“…Our finding that passive stepping suppressed the magnitude of the forearm H-reflex is well in line with previous reports (Frigon et al 2004;Loadman and Zehr 2007;Zehr et al 2007) of conditioning by remote rhythmic movement. However, one possible discrepancy between our study and previous ones is the possible substantial contribution of the voluntary drive to maintain rhythmic leg movements.…”

“…3 and 4). Indeed, the specific source of the modulation is not certain, although these findings may indicate that the phasic afferent inputs arising from passive leg movements are conveyed to the ascending, long propriospinal neurons responsible for the inhibition of the monosynaptic reflex arc in the other segments of the spinal cord (Alstermark et al 1987;Cheng et al 1998;Dietz 2002;Frigon et al 2004;Loadman and Zehr 2007;Misiaszek et al 1998;Zehr and Duysens 2004). More recently, de Ruiter et al (2010) reported that suppression of the Sol H-reflex amplitude Fig.…”

“…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. In addition, further investigation is needed to elucidate the functional implication of walking-related afferent signals on remote Hreflex suppression during walking.…”

“…DURING RHYTHMIC ARM CYCLING, Hoffmann (H)-reflex amplitude in the soleus muscle (Sol) is strongly suppressed in humans (Frigon et al 2004;Hundza and Zehr 2009;Loadman and Zehr 2007). Interestingly, leg cycling also leads to suppression of the H-reflex amplitude in the forearm muscles .…”

Reflex modulation during rhythmic limb movements in humans

“…One of the underlying mechanisms for these reflex modulations may be regulation at the premotoneuronal level. Frigon et al 70) demonstrated that sural nerve stimulation facilitated H-reflexes in the soleus (Sol) at shoulder extension, but not at shoulder flexion during static and arm cycling, and that common peroneal nerve (CP) stimulation significantly reduced Sol H-reflex amplitude during static and cycling tasks (see Fig. 3).…”