Abstract
BackgroundHuman bipedal gait benefits from arm swing, as it drives and shapes lower limb muscle activity in healthy participants as well as patients suffering from neurological impairment. Also during gait initiation, arm swing instructions were found to facilitate leg muscle recruitment. Research questionThe aim of the present study is to exploit the directional decomposition of coherence to examine to what extent forward and backward arm swing contribute to leg muscle recruitment during gait initiation. MethodsAmbulant electromyography (EMG) from shoulder muscles (deltoideus anterior and posterior) and upper leg muscles (biceps femoris and rectus femoris) was analysed during gait initiation in nineteen healthy participants (median age of 67 ± 12 (IQR) years). To assess to what extent either deltoideus anterior or posterior muscles were able to drive upper leg muscle activity during distinct stages of the gait initiation process, time dependent intermuscular coherence was decomposed into directional components based on their time lag (i.e. forward, reverse and zero-lag). ResultsCoherence from the forward directed components, representing shoulder muscle signals leading leg muscle signals, revealed that deltoideus anterior (i.e. forward arm swing) and deltoideus posterior (i.e. backward arm swing) equally drive upper leg muscle activity during the gait initiation process. SignificanceThe presently demonstrated time dependent directional intermuscular coherence analysis could be of use for future studies examining directional coupling between muscles or brain areas relative to certain gait (or other time) events. In the present study, this analysis provided neural underpinning that both forward and backward arm swing can provide neuronal support for leg muscle recruitment during gait initiation and can therefore both serve as an effective gait rehabilitation method in patients with gait initiation difficulties.
Highlights
Human bipedal gait exhibits a four-limb pattern that is comparable to that of quadrupeds, with arms swinging in anti-phase with the ipsilateral leg as if they are a remnant of neural connections used in quadrupedal gait
As in a previous study we found that neural coupling was most pronounced between shoulder muscles and upper leg muscles in healthy participants [4], we focused on analysing bilateral deltoideus muscles and the rectus femoris and biceps femoris muscles
We found that the deltoideus anterior and posterior exhibit equal forward directed coherence with upper leg muscles during gait initiation
Summary
Human bipedal gait exhibits a four-limb pattern that is comparable to that of quadrupeds, with arms swinging in anti-phase with the ipsilateral leg as if they are a remnant of neural connections used in quadrupedal gait. Besides its role in steady state gait, enhanced arm swing was found to facilitate impaired gait initiation in Parkinson patients on a behavioural and cortico-muscular level [5] All these studies were primarily based on the instruction of producing or enhancing forward arm swing (i.e. anteflexion of the shoulder), whereas the deltoideus posterior, which is responsible for retroflexion of the shoulder (i.e. backward arm swing), exhibits active muscle activity during gait [6,7] and gait initiation [5]. This analysis provided neural underpinning that both forward and backward arm swing can provide neuronal support for leg muscle recruitment during gait initiation and can both serve as an effective gait rehabilitation method in patients with gait initiation difficulties
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