Changes in Reciprocal Inhibition Across the Ankle Joint With Changes in External Load and Pedaling Rate During Bicycling

Richards

et al. 2016

Front. Hum. Neurosci.

The purpose of this study was to examine the influence of neutral and pronated handgrip positions on corticospinal excitability to the biceps brachii during arm cycling. Corticospinal and spinal excitability were assessed using motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation (TMS) and cervicomedullary-evoked potentials (CMEPs) elicited via transmastoid electrical stimulation (TMES), respectively. Participants were seated upright in front on arm cycle ergometer. Responses were recorded from the biceps brachii at two different crank positions (6 and 12 o’clock positions relative to a clock face) while arm cycling with neutral and pronated handgrip positions. Responses were also elicited during tonic elbow flexion to compare/contrast the results to a non-rhythmic motor output. MEP and CMEP amplitudes were significantly larger at the 6 o’clock position while arm cycling with a neutral handgrip position compared to pronated (45.6 and 29.9%, respectively). There were no differences in MEP and CMEP amplitudes at the 12 o’clock position for either handgrip position. For the tonic contractions, MEPs were significantly larger with a neutral vs. pronated handgrip position (32.6% greater) while there were no difference in CMEPs. Corticospinal excitability was higher with a neutral handgrip position for both arm cycling and tonic elbow flexion. While spinal excitability was also higher with a neutral handgrip position during arm cycling, no difference was observed during tonic elbow flexion. These findings suggest that not only is corticospinal excitability to the biceps brachii modulated at both the supraspinal and spinal level, but that it is influenced differently between rhythmic arm cycling and tonic elbow flexion.

Section: Introductionmentioning

confidence: 99%

Changes in Corticospinal and Spinal Excitability to the Biceps Brachii with a Neutral vs. Pronated Handgrip Position Differ between Arm Cycling and Tonic Elbow Flexion

Richards

et al. 2016

Front. Hum. Neurosci.

The Journal of Physiology

“…In the cat, Ia inhibitory interneurones projecting to extensor motoneurones are active when their target motoneurones are inactive and stimulation of the Ia inhibitory pathway evokes the largest IPSPs in the target motoneurones in their hyperpolarized phase during locomotion (Pratt & Jordan, 1987). Similarly, in human subjects disynaptic Ia inhibition from ankle dorsiflexors to ankle plantar flexors is largest in the swing phase of gait (Petersen et al 1999), in the upstroke phase during bicycling (Pyndt et al 2003) and during a voluntary ankle dorsiflexion in sitting subjects (Crone & Nielsen, 1989). At least partly as a consequence of this inhibition of soleus motoneurones, the soleus H-reflex is reduced at a similar time during these movements (Crone & Nielsen, 1989).…”

Section: Introductionmentioning

confidence: 99%

Voluntary activation of ankle muscles is accompanied by subcortical facilitation of their antagonists

Geertsen

Zuur

Nielsen

2010

Flexion and extension movements are organized reciprocally, so that extensor motoneurones in the spinal cord are inhibited when flexor muscles are active and vice versa. During and just prior to dorsiflexion of the ankle, soleus motoneurones are thus inhibited as evidenced by a depression of the soleus H-reflex. It is therefore surprising that soleus motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) have been found not to be reduced and even facilitated during a voluntary dorsiflexion. The objective of this study was to investigate if MEPs, evoked by TMS, show a similar facilitation prior to and at the onset of contraction of muscles that are antagonists to the muscle in which the MEP is evoked and if so, examine the origin of such a facilitatory motor programme. Eleven seated subjects reacted to an auditory cue by contracting either the tibialis anterior (TA) or soleus muscle of the left ankle. TMS was applied to the hotspot of TA and soleus muscles on separate days. Stimuli were delivered prior to and at the beginning of contraction. Soleus MEPs were significantly facilitated when TMS was applied 50 ms prior to onset of plantar flexion. Surprisingly, soleus MEPs were also facilitated (although to a lesser extent) at a similar time in relation to the onset of dorsiflexion. TA MEPs were facilitated 50 ms prior to onset of dorsiflexion and neither depressed nor facilitated prior to plantar flexion. No difference was found between the facilitation of the soleus MEP and motor evoked responses to cervicomedullary stimulation prior to dorsiflexion, suggesting that the increased soleus MEPs were not caused by changes at a cortical level. This was confirmed by the observation that short-latency facilitation of the soleus H-reflex by subthreshold TMS was increased prior to plantar flexion, but not prior to dorsiflexion. These findings suggest that voluntary contraction at the ankle is accompanied by preceding facilitation of antagonists by a subcortical motor programme. This may help to ensure that the direction of movement may be changed quickly and efficiently during functional motor tasks.

Journal of Neurophysiology

“…In humans, the gain of spinal reflex pathways and ascending sensory pathways has been shown to be differentially modulated by changes in locomotor intensity (Hundza et al 2012;Hundza and Zehr 2009;Larsen et al 2006;Pyndt et al 2003;Sakamoto et al 2004). Most of these studies report velocity-or cadencedependent modulation, although load-dependent modulation in supraspinal and spinal reflex excitability has also been reported.…”

Section: Introductionmentioning

confidence: 99%

Intensity matters: effects of cadence and power output on corticospinal excitability during arm cycling are phase and muscle dependent

Lockyer

Benson

Hynes

et al. 2018

Lockyer EJ, Benson RJ, Hynes AP, Alcock LR, Spence AJ, Button DC, Power KE. Intensity matters: effects of cadence and power output on corticospinal excitability during arm cycling are phase and muscle dependent. The present study investigated the effects of cadence and power output on corticospinal excitability to the biceps (BB) and triceps brachii (TB) during arm cycling. Supraspinal and spinal excitability were assessed using transcranial magnetic stimulation (TMS) of the motor cortex and transmastoid electrical stimulation (TMES) of the corticospinal tract, respectively. Motor-evoked potentials (MEPs) elicited by TMS and cervicomedullary motor-evoked potentials (CMEPs) elicited by TMES were recorded at two positions during arm cycling corresponding to mid-elbow flexion and mid-elbow extension (i.e., 6 and 12 o'clock made relative to a clock face, respectively). Arm cycling was performed at combinations of two cadences (60 and 90 rpm) at three relative power outputs (20, 40, and 60% peak power output). At the 6 o'clock position, BB MEPs increased~11.5% as cadence increased and up to~57.2% as power output increased (P Ͻ 0.05). In the TB, MEPs increased~15.2% with cadence (P ϭ 0.013) but were not affected by power output, while CMEPs increased with cadence (~16.3%) and power output (up to~19.1%, P Ͻ 0.05). At the 12 o'clock position, BB MEPs increased~26.8% as cadence increased and up to~96.1% as power output increased (P Ͻ 0.05), while CMEPs decreased~29.7% with cadence (P ϭ 0.013) and did not change with power output (P ϭ 0.851). In contrast, TB MEPs were not different with cadence or power output, while CMEPs increased 12.8% with cadence and up to~23.1% with power output (P Ͻ 0.05). These data suggest that the "type" of intensity differentially modulates supraspinal and spinal excitability in a manner that is phase-and muscle dependent. NEW & NOTEWORTHYThere is currently little information available on how changes in locomotor intensity influence excitability within the corticospinal pathway. This study investigated the effects of arm cycling intensity (i.e., alterations in cadence and power output) on corticospinal excitability projecting to the biceps and triceps brachii during arm cycling. We demonstrate that corticospinal excitability is modulated differentially by cadence and power output and that these modulations are dependent on the phase and the muscle examined.