Intra- and Intermuscular Coherence and Body Acceleration Control in Older Adults during Bipedal Stance

Differences in corticospinal drive and co-activations of antagonist muscles during forward leaning and backward returning tasks between children and young adults

BACKGROUND

Postural control imposes higher demands on the central neural system (CNS), and age-related declines or incomplete CNS development often result in challenges performing tasks like forward postural leaning. Studies on older adults suggest increased variability in center of pressure (COP), greater muscle co-activations, and reduced corticospinal control during forward leaning tasks. However, the understanding of these features in children remains unclear. Specifically, it is uncertain whether forward leaning poses greater challenges for young children compared to adults, given the ongoing maturation of CNS during development. Understanding the distinct neuromuscular patterns observed during postural leaning could help optimize therapeutic strategies aimed at improving postural control in pediatric populations.

METHODS

12 typically developing children (5.91 ± 1.37 years) and 12 healthy young adults (23.16 ± 1.52 years) participated in a dynamic leaning forward task aimed at matching a COP target in the anterior-posterior direction as steadily as possible. Participants traced a triangular trajectory involving forward leaning (FW phase) to 60 % of their maximum lean distance and backward returning (BW phase) to the neutral standing position. Surface electromyography (sEMG) from muscles including gastrocnemius medialis (GM), soleus (SOL), and tibialis anterior (TA) were collected during both phases. COP variability was assessed using the standard deviation (SD) of COP displacements. Muscle co-activation indexes (CI) for ankle plantar and dorsal flexors (SOL/TA, GM/TA) were derived from sEMG activities. Intermuscular coherence in the beta band (15-30 Hz) was also analyzed to evaluate corticospinal drive.

RESULTS

Children exhibited a significantly greater SD of COP compared to young adults (p < 0.01) during the BW phase. They also demonstrated higher CI (p < 0.05) and reduced coherence of SOL/TA (p < 0.05) compared to young adults during this phase. No significant group differences were observed during the FW phase. Within the children's group, COP variability was significantly higher in the BW phase compared to the FW phase (p < 0.01). Moreover, children displayed greater CI (p < 0.01) and reduced coherence of SOL/TA (p < 0.01) during the BW phase compared to the FW phase. Conversely, no significant phase effects were observed in the adult group. Furthermore, sEMG measures were significantly correlated with COP variability (p < 0.05).

CONCLUSIONS

The findings of this small study suggest that age-related differences in CNS development influence the modulation of corticospinal drive to ankle muscles (e.g., SOL/TA) during childhood, particularly supporting the existence of a separate pathway underlying the control of forward lean and backward returning.

Intermuscular Coherence during Quiet Standing in Sub-Acute Patients after Stroke: An Exploratory Study

Asymmetrically impaired standing control is a prevalent disability among stroke patients; however, most of the neuromuscular characteristics are unclear. Therefore, the main purpose of this study was to investigate between-limb differences in intermuscular coherence during quiet standing. Consequently, 15 patients who had sub-acute stroke performed a quiet standing task without assistive devices, and electromyography was measured on the bilateral tibialis anterior (TA), soleus (SL), and medial gastrocnemius (MG). The intermuscular coherence of the unilateral synergistic (SL-MG) pair and unilateral antagonist (TA-SL and TA-MG) pairs in the delta (0-5 Hz) and beta (15-35 Hz) bands were calculated and compared between the paretic and non-paretic limbs. The unilateral synergistic SL-MG coherence in the beta band was significantly greater in the non-paretic limb than in the paretic limb (p = 0.017), while unilateral antagonist TA-MG coherence in the delta band was significantly greater in the paretic limb than in the non-paretic limb (p < 0.01). During quiet standing, stroke patients showed asymmetry in the cortical control of the plantar flexor muscles, and synchronous control between the antagonistic muscles was characteristic of the paretic limb. This study identified abnormal muscle activity patterns and asymmetrical cortical control underlying impaired standing balance in patients with sub-acute stroke using an intermuscular coherence analysis.

EMG-EMG coherence during voluntary control of human standing tasks: a systematic scoping review

Background

Intra- or inter-muscular (EMG-EMG) coherence is a simple and non-invasive method for estimating central nervous system control during human standing tasks. Although this research area has developed, no systematic literature review has been conducted.

Objectives

We aimed to map the current literature on EMG-EMG coherence during various standing tasks to identify the research gaps and summarize previous studies comparing EMG-EMG coherence between healthy young and elderly adults.

Methods

Electronic databases (PubMed, Cochrane Library, and CINAHL) were searched for articles published from inception to December 2021. We incorporated studies that analyzed EMG-EMG coherence of the postural muscles in various standing tasks.

Results

Finally, 25 articles fulfilled the inclusion criteria and involved 509 participants. Most participants were healthy young adults, while only one study included participants with medical conditions. There was some evidence that EMG-EMG coherence could identify differences in standing control between healthy young and elderly adults, although the methodology was highly heterogeneous.

Conclusion

The present review indicates that EMG-EMG coherence may help elucidate changes in standing control with age. In future studies, this method should be used in participants with central nervous system disorders to understand better the characteristics of standing balance disabilities.