RESUMEN
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⯱â¯1.37â¯years) and 12 healthy young adults (23.16⯱â¯1.52â¯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 60â¯% 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 (15-30â¯Hz) was also analyzed to evaluate corticospinal drive. RESULTS: Children exhibited a significantly greater SD of COP compared to young adults (pâ¯<â¯0.01) during the BW phase. They also demonstrated higher CI (pâ¯<â¯0.05) and reduced coherence of SOL/TA (pâ¯<â¯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 (pâ¯<â¯0.01). Moreover, children displayed greater CI (pâ¯<â¯0.01) and reduced coherence of SOL/TA (pâ¯<â¯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 (pâ¯<â¯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.
RESUMEN
Aging can impair an ability to lean the body forward to the edge of the base of support. Here, we investigated, using a coherence analysis, common inputs to bilateral and unilateral plantar flexor muscles to test a hypothesis that the age-related impairment would be related to strong synchronous bilateral activation and reduced cortical control of these muscles. Healthy young (n = 14) and elderly adults (n = 19), who were all right-foot dominant, performed quiet standing task and tasks that required the subjects to lean their body forward to 35 and 75% of the maximum lean distance. The electromyogram was recorded from the bilateral medial gastrocnemius (MG) and soleus (SL) muscles. We analyzed delta-band coherence, that reflects comodulation of muscle activity, between the bilateral homologous muscles (MG-MG and SL-SL pairs). The origin of this bilateral comodulation is suggested to be the subcortical system. Also, we examined beta-band coherence, that is related to the corticospinal drive, between the unilateral muscles (MG-SL pair) in the right leg. Results indicated that the bilateral delta-band coherence for the MG-MG pair was significantly smaller in the 75% forward lean than quiet standing and 35% forward lean tasks for the young adults (quiet: p = 0.036; 35%: p = 0.0011). The bilateral delta-band coherence for the SL-SL pair was significantly smaller in the 75% forward lean than 35% forward lean task for the young adults (p = 0.027). Furthermore, the unilateral beta-band coherence was larger in the forward lean than quiet standing task for the young adults (35%: p < 0.001; 75%: p = 0.029). Contrarily, the elderly adults did not demonstrate such changes. These findings suggest the importance of decreasing the synchronous bilateral activation and increasing the unilateral cortical control of the plantar flexor muscles for the successful forward postural lean performance, and that aging impairs this modulatory ability.