Altered neuromuscular strategies are suggested to contribute to age-related decreases in postural stability. Current approaches tend to overlook global (whole body) neuromuscular postural control strategies, potentially due to methodological constraints or residual influence from a longstanding, but outdated, biomechanical view in which postural sway is represented by a single-jointed inverted pendulum. In this study, we investigate age-related differences in postural strategies during upright static balance maintenance by assessing global neuromuscular control. We collected simultaneous posturography and electromyography (EMG) data from young (18–35 years, n = 32) and older (65–85 years, n = 33) participants while they stood upright on a force plate or on foam pads thereon, with eyes open or closed. Postural instability was assessed by the standard deviation and velocity of the center of pressure. EMG sensors recorded the activity of thirty muscles (15 on each hemibody). Co-contraction across all muscle pairs was measured with Falconer’s co-contraction index (CCI), and muscle synergy with non-negative matrix factorization. The older group possessed increased global co-contraction intensity, marked by more frequent use of a knee extensor synergy, and was more unstable than the younger group. Notably, advancing age modulated the variability of co-contraction intensity, where the oldest individuals consistently adopted a pure co-contraction strategy marked by the highest CCI values and lowest variability. Age-corrected correlations revealed that knee extensor CCI values were significantly related to postural instability. Taken together, global co-contraction appears to be a signature of elderly postural strategy and age-related instability may be directly related to the extent of knee extensor co-contraction. These results stress the importance of zooming out from classical agonist–antagonist muscle pair investigations in the endeavor to understand elderly postural control strategy.

As humans, we seamlessly hold objects in our hands, and may even lose consciousness of these objects. This phenomenon raises the unsettled question of the involvement of the cerebral cortex, the core area for voluntary motor control, in dynamically maintaining steady muscle force. To address this issue, we measured magnetoencephalographic brain activity from healthy adults who maintained a steady pinch grip. Using a novel analysis approach, we uncovered fine-grained temporal modulations in the beta sensorimotor brain rhythm and its coupling with muscle activity, with respect to several aspects of muscle force (rate of increase/decrease or plateauing high/low). These modulations preceded changes in force features by ∼40 ms and possessed behavioral relevance, as less salient or absent modulation predicted a more stable force output. These findings have consequences for the existing theories regarding the functional role of cortico-muscular coupling, and suggest that steady muscle contractions are characterized by a stable rather than fluttering involvement of the sensorimotor cortex.

Voluntary motor control is thought to be predicated on the ability to efficiently integrate and process somatosensory afferent information. However, current approaches in the field of motor control have not factored in objective markers of how the brain tracks incoming somatosensory information. Here, we asked whether motor performance relates to such markers obtained with an analysis of the coupling between peripheral kinematics and cortical oscillations during continuous movements, best known as corticokinematic coherence (CKC). Motor performance was evaluated by measuring both gross and fine motor skills using the Box and Blocks Test (BBT) and the Purdue Pegboard Test (PPT), respectively, and with a biomechanics measure of coordination. A total of 61 participants completed the BBT, while equipped with electroencephalography and electromyography, and the PPT. We evaluated CKC, from the signals collected during the BBT, as the coherence between movement rhythmicity and brain activity, and coordination as the cross-correlation between muscle activity. CKC at movements’ first harmonic was positively associated with BBT scores (r = 0.41,p = 0.001), and alone showed no relationship with PPT scores (r = 0.07,p = 0.60), but in synergy with BBT scores, participants with lower PPT scores had higher CKC than expected based on their BBT score. Coordination was not associated with motor performance or CKC (p > 0.05). These findings demonstrate that cortical somatosensory processing in the form of strengthened brain–peripheral coupling is specifically associated with better gross motor skills and thus may be considered as a valuable addition to classical tests of proprioception acuity.

While the simultaneous degradation of muscle composition and postural stability in aging are independently highly investigated due to their association with fall risk, the interplay between the two has received little attention. Thus, the purpose of this study is to explore how age-related changes in muscle composition relate to postural stability. To that aim, we collected posturography measures and ultrasound images of the dominant Vastus Lateralis and Biceps Brachii from 32 young (18–35 year old) and 34 older (65–85 year old) participants. Muscle properties were quantified with echo-intensity and texture-based metrics derived from gray-level co-occurrence matrix analysis, and postural stability with the variability of the center of pressure during bipedal stance tasks. Ultrasound parameters revealed that young muscle possessed lower echo-intensity and higher homogeneity compared to the elderly. Echo-intensity and muscle thickness, and several texture-based parameters possessed outstanding young versus older classification performance. A canonical correlation analysis demonstrated a significant relationship between ultrasound and postural measures only within the young group (r = 0.53, p < 0.002), where those with ‘better’ muscle composition displayed larger postural sways. Our results indicate that, in older individuals, postural stability and muscle composition, two common fall risk factors, are unrelated. In view of this decoupling, both may contribute independently to fall risk. Furthermore, our data support the view that texture-based parameters provide a robust alternative to echo-intensity in providing markers of muscle composition.

Maintaining balance requires a complex interplay between sensory and motor processes, and this ability deteriorates with age, impairing daily life activities and contributes to increased fall risks. Importantly, while cognitive-motor interference paradigms suggest an aging-related increase in the cortical involvement in balance regulation, direct evidence remains lacking. To clarify this issue, we assessed the effect of aging on sway-based corticokinematic coherence (CKC), which is a measure of the coupling between cortical electrophysiological signals and postural sway. To that end, we recorded the center-of-pressure fluctuations and electroencephalographic cortical activity of 64 young and 67 older healthy participants performing balance tasks during which sensory information was either removed or altered. We found that older adults showed increased cortical activity that appears to relate to different aspects of closed loop postural control during challenging balance conditions, and correlates with upright stance stability. They also showed increased delays between cortical activity and postural sway, indicative of slower central processing speed. Finally, despite the older cohort displaying significantly altered vestibulo-ocular reflexes, no relationship was found with CKC strength. Overall, our results provide direct evidence that cortical involvement in balance regulation increases with aging. They suggest the feasibility of assessing afferent and efferent processing during balance maintenance, paving the way for studies identifying neurophysiological determinants of fall risks.

Voluntary motor control is thought to be predicated on the ability to efficiently integrate and process somatosensory afferent information. However, current approaches in the field of motor control have not factored in objective markers of how the brain actually tracks incoming somatosensory information. Here, we asked whether motor performance relates with such markers obtained with an analysis of the coupling between peripheral kinematics and cortical oscillations during continuous movements, best known as corticokinematic coherence (CKC). Motor performance was evaluated by measuring both gross and fine motor skills using the Box and Blocks Test (BBT) and the Purdue Pegboard Test (PPT), respectively, and with a biomechanics measure of coordination. Sixty-one participants completed the BBT, while equipped with electroencephalography and electromyography, and the PPT. We evaluated CKC, from the signals collected during the BBT, as the coherence between movement rhythmicity and brain activity, and coordination as the cross-correlation between muscle activity. CKC at movements’ first harmonic was positively associated with BBT scores, and showed a relationship with PPT scores, but only in synergy with BBT scores, where participants with lower PPT score had higher CKC than expected based on their BBT score. Coordination was not associated with motor performance and at most, weakly related to CKC. These findings demonstrate that cortical somatosensory processing in the form of strengthened brain-peripheral coupling is specifically associated with better gross motor skills. CKC might be considered as a valuable addition to classical tests of proprioceptive acuity, with important perspectives for future clinical studies and practice. Significance Statement Whether standing upright, jogging, or in Olympic competition, our nervous system not only sends out motor commands prompting muscles to contract, but also receives incoming information to fine-tune motor actions. Though the machinery involved in sensing mechanical changes is well-described, the neural processing of this information is not, making its relevance to motor function unresolved. We found that the coupling strength between peripheral kinematics and cortical activity was related to motor function and at most, only weakly related to conventional muscle-only assessments. We present novel behavioral relevance of this coupling and its specific relationship to gross motor skill. Our study paves the way for including novel brain-centered approaches to complement classical assessment sensorimotor functions in health and disease.