Stand Up to Excite the Spine: Neuromuscular, Autonomic, and Cardiometabolic Responses During Motor Imagery in Standing vs. Sitting Posture.

Sidney Grosprêtre,Laurie Isacco,Gael Ennequin,Laurent Mourot,Uros Marusic,Philippe Gimenez

doi:10.3389/fphys.2021.762452

Abstract

Motor imagery (MI) for health and performance strategies has gained interest in recent decades. Nevertheless, there are still no studies that have comprehensively investigated the physiological responses during MI, and no one questions the influence of low-level contraction on these responses. Thus, the aim of the present study was to investigate the neuromuscular, autonomic nervous system (ANS), and cardiometabolic changes associated with an acute bout of MI practice in sitting and standing condition. Twelve young healthy males (26.3 ± 4.4 years) participated in two experimental sessions (control vs. MI) consisting of two postural conditions (sitting vs. standing). ANS, hemodynamic and respiratory parameters, body sway parameters, and electromyography activity were continuously recorded, while neuromuscular parameters were recorded on the right triceps surae muscles before and after performing the postural conditions. While MI showed no effect on ANS, the standing posture increased the indices of sympathetic system activity and decreased those of the parasympathetic system (p < 0.05). Moreover, MI during standing induced greater spinal excitability compared to sitting posture (p < 0.05), which was accompanied with greater oxygen consumption, energy expenditure, ventilation, and lower cardiac output (p < 0.05). Asking individuals to perform MI of an isometric contraction while standing allows them to mentally focus on the motor command, not challenge balance, and produce specific cardiometabolic responses. Therefore, these results provide further evidence of posture and MI-related modulation of spinal excitability with additional autonomic and cardiometabolic responses in healthy young men.

Highlights

Motor function in sport performance or rehabilitation could be improved by mental training
The data of the present study can be divided into four main domains between which the effects of motor imagery (MI) and posture were compared, namely, cardiometabolic (V O2, EE, Respiratory quotient (RQ), cardiac output (CO), etc.), autonomous nervous system (HRV, baroreflex etc.), central nervous system (EMG activities, H-reflexes, V-waves, etc.), and posture (CoP length, area, etc.) data
As there was no duration effect during CTRL sessions and no sequence effect during MI training sessions, the mean value during each posture for each condition is considered for the following analyses

Summary

Introduction

Motor function in sport performance or rehabilitation could be improved by mental training. Numerous previous studies have shown that motor brain areas are activated during MI, such as the parietal, premotor, and primary motor cortices (Decety et al, 1994; Lotze et al, 1999; Grèzes and Decety, 2001; Ehrsson et al, 2003; Guillot et al, 2009; Munzert et al, 2009; Kilintari et al, 2016). Some recent evidence highlighted that this minor activation of motor regions possibly generates a sub-threshold brain output, which could reach spinal levels. It has been suggested that such subthreshold cortical output was susceptible to partially reach the spinal networks by affecting the most sensitive structures, i.e., the spinal interneurons (Grosprêtre et al, 2014). It was shown that repetition of this minor stimulus, such as after an acute bout of mental practice, may increase the sensitivity of all spinal structures (Grosprêtre et al, 2019)

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