Abstract
Mechanical muscle-tendon vibration affects musculature and the nervous system. As the vibrations used in previous studies were varied, consistently determining the effect of mechanical vibration was challenging. Additionally, only a few studies have applied vibrations to dynamic motion. This study investigated whether the vibration based on the sensorimotor response could affect the stability and function of stair climbing. Electroencephalogram (EEG) signals were recorded from the sensorimotor area, and mu rhythms, dependent on the vibration frequencies, were analyzed. Based on the analysis, the vibratory stimulus conditions were set and applied to the Achilles tendon of the lower limb during stair climbing. Simultaneously, electromyogram (EMG) signals from the gastrocnemius lateralis (GL), gastrocnemius medialis (GM), soleus (SOL), and tibialis anterior (TA) were recorded. Activations and co-activations of the shank muscles were analyzed according to the phases of stair climbing. When vibration was applied, the TA activation decreased in the pull-up (PU) phase, and calf muscle activations increased during the forward continuous (FCN) phase. These changes and their degrees differ significantly between stimulus conditions (p < 0.05). Co-activation changes, which differed significantly with conditions (p < 0.05), appeared mostly in the PU. These results imply that the vibration affects stability and function of stair climbing, suggesting that the vibration characteristics should be considered when they are applied to dynamic movement.
Highlights
Stair climbing is a motion that combines a forward movement and an ascent performed simultaneously; it requires a stable body support and joint stiffness
All vibratory conditions were applied with threshold intensity (Th-) and the sub-threshold intensity (Sub-)
This study investigated changes in the mu rhythm with vibration frequency, and changes in the EMG and co-activation caused by the local vibratory characteristics based on the mu rhythm and the perception thresholds during stair climbing
Summary
Stair climbing is a motion that combines a forward movement and an ascent performed simultaneously; it requires a stable body support and joint stiffness. Co-activation describes the simultaneous activation or co-contraction in the agonist and antagonist muscles around the joint [1,2,3]. The role of muscle co-activation is known to be that of increasing joint stiffness of the upper or lower limbs, thereby increasing joint stability [3,4]. Tadayoshi Asaka et al [5] have confirmed that muscle co-activation increases when standing on an unstable board. Have reported that subjects use co-contraction control to offset unstable forces in a static state [6]. Solomonow et al [7] have found that increased co-activation during strong contractions can protect joints and maintain stability.
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