Age, Cognitive Task, and Arm Position Differently Affect Muscle Synergy Recruitment but have Similar Effects on Walking Balance

Effects of arm movement on emotional state and walking outcomes during height-induced postural threat in healthy young adults

BACKGROUND

There is evidence that height-induced postural threat leads to detrimental effects on walking performance. However, little is known about how the additional restriction of stabilizing arm movements affects gait and emotional state outcomes.

OBJECTIVE

The purpose was to investigate how the restriction of arm movement affects subjective and objective balance-related measures during walking at or above ground-level.

METHODS

Twenty-two healthy young adults (11 males, 11 females; mean ± SD age; 24.4 ± 4.9 years) walked five meters at self-selected speed on ground-level (no threat) and 80 cm above ground-level (threat) with free and restricted arm movement. Emotional state outcomes were quantified by assessing self-reported balance confidence, fear of falling, perceived instability, and conscious balance processing. Walking outcomes (i.e., gait velocity, cadence, step time, normal impulse) were calculated using pressure-detecting insoles.

RESULTS

Irrespective of arm movement condition, height-induced postural threat evoked a decrease in balance confidence and increases in fear of falling, perceived instability, and conscious balance processing as well as deteriorations in walking outcomes (i.e., decrease in gait speed and cadence; increase in step time and normal impulse). For balance confidence and step time, the threat-induced impairments were further amplified when arm movements were restricted.

CONCLUSIONS

The strengthening of the height-induced deteriorations in emotional state (balance confidence) and walking (step time) outcomes due to the restriction of the arm movements emphasizes the importance of stabilizing, free arm movements ('upper body strategy') for dynamic postural control.

Help! - you need your hands: Contribution of arm movements on balance performance in healthy individuals: A systematic review with meta-analysis

BACKGROUND

Emerging evidence highlights that arm movements exert a substantial and functionally relevant contribution on postural control in healthy individuals. However, performance differences between free versus restricted arm movement for different balance categories with varying levels of task difficulty have not been systematically investigated yet.

OBJECTIVE

The objective of this systematic review and meta-analysis was to characterise, aggregate, and quantify performance discrepancies between free and restricted arm movement conditions for diverging balance categories with varying levels of task difficulty in healthy individuals.

METHODS

A systematic search of the literature according to the PRISMA guidelines was performed on the electronic databases PubMed, Web of Science, and SPORTDiscus from their inception date till 1st September 2024. To be applicable for analysis, studies had to report at least one measure of balance performance in healthy individuals. The included studies were coded according to the following criteria: age, sex, status, arm movement conditions, balance test, and test modality. Methodological study quality was assessed using the Appraisal tool for Cross-Sectional Studies. Weighted standardized mean differences (SMD) were calculated and classified according to their magnitude.

RESULTS

The literature search identified a total of N = 941 records, 25 of which met the inclusion criteria and were analysed in this review. A total of 725 participants (n = 331 females) participated in the studies. The free use of arm movement resulted in moderate (static: SMD = 0.51, dynamic: SMD = 0.66, proactive: SMD = 0.52, reactive: SMD = 0.50) improvements of balance performance. In addition, the performance enhancements were more pronounced for balance tasks with a high (static: SMD = 0.89, dynamic: SMD = 1.04) compared to a low (static: SMD = 0.20, dynamic: SMD = 0.76) difficulty level. Due to a lack of studies, no analysis for measures of proactive and reactive balance was performed.

CONCLUSIONS

The findings revealed that the free use of arm movement positively affects several measures of balance performance, and this is effect is more pronounced for balance tasks with a high difficulty level.

The Effect of Cognitive and Motor Dual Tasks on the Synergy of Lower Limb Muscles During Walking

OBJECTIVE

Walking is one of the most complex human movements that can be affected by various sources of attention. Dual tasks reduce attention, increase information processing, and may alter control mechanisms such as synergy. However, the effect of dual tasks on muscle synergy remains unknown. Therefore, this study aimed to investigate the effect of cognitive and motor dual tasks on the synergy of lower limb muscles during walking.

METHODS

Twenty-four participants were selected voluntarily. The activity of the eight lower limb muscles was recorded under three different conditions: normal walking without a dual task, walking with a cognitive dual task, and walking with a motor dual task. A nonnegative matrix factorization algorithm and the variance accounted for were used to extract muscle synergy. The repeated-measures analysis of variance test and Pearson's correlation coefficient were performed to analyze the data.

RESULTS

In this study, five muscle synergies were extracted from electromyography data using the variance accounted for method under three different conditions. The pattern of muscle synergies showed moderate to strong correlations. Peaks of synergies changed, and a time shift in synergy peaks during walking was observed. However, the number of extracted synergies did not change.

CONCLUSION

The number of recruited muscle synergies remained consistent across different conditions. Dual tasks affect the higher levels of the motor control system, causing interference in information processing that leads to a shift in the tendency of synergy and weight coefficients of the muscles, ultimately resulting in a change in walking mechanics.

Age-related changes in muscle coordination patterns of stepping responses to recover from loss of balance

INTRODUCTION

Reactive stepping capacity to recover from a loss of balance declines with aging, which increases the risk of falling. To gain insight into the underlying mechanisms, we investigated whether muscle coordination patterns of reactive stepping differed between healthy young and older individuals.

METHODS

We performed a cross-sectional study between 15 healthy young and 14 healthy older adults. They recovered from 200 multidirectional platform translations that evoked reactive stepping responses. We determined spatiotemporal step variables and used muscle synergy analysis to characterize stance- and swing-leg muscle coordination patterns from the start of perturbation until foot landing.

RESULTS

We observed delayed step onsets in older individuals, without further spatiotemporal differences. Muscle synergy structure was not different between young and older individuals, but age-related differences were observed in the time-varying synergy activation patterns. In anterior-posterior directions, the older individuals demonstrated significantly enhanced early swing-leg synergy activation consistent with non-stepping behavior. In addition, around step onset they demonstrated increased levels of synergy coactivation (mainly around the ankle) in lateral and anterior directions, which did not appear to hamper foot clearance.

CONCLUSION

Although synergy structure was not affected by age, the delayed step onsets and the enhanced early synergy recruitment point at a relative bias towards non-stepping behavior in older adults. They may need more time for accumulating information on the direction of perturbation and making the corresponding sensorimotor transformations before initiating the step. Future work may investigate whether perturbation-based training improves these age-related deficits.

Rectified Latent Variable Model-Based EMG Factorization of Inhibitory Muscle Synergy Components Related to Aging, Expertise and Force-Tempo Variations

Muscle synergy has been widely acknowledged as a possible strategy of neuromotor control, but current research has ignored the potential inhibitory components in muscle synergies. Our study aims to identify and characterize the inhibitory components within motor modules derived from electromyography (EMG), investigate the impact of aging and motor expertise on these components, and better understand the nervous system's adaptions to varying task demands. We utilized a rectified latent variable model (RLVM) to factorize motor modules with inhibitory components from EMG signals recorded from ten expert pianists when they played scales and pieces at different tempo-force combinations. We found that older participants showed a higher proportion of inhibitory components compared with the younger group. Senior experts had a higher proportion of inhibitory components on the left hand, and most inhibitory components became less negative with increased tempo or decreased force. Our results demonstrated that the inhibitory components in muscle synergies could be shaped by aging and expertise, and also took part in motor control for adapting to different conditions in complex tasks.

Muscle Recruitment Strategies in a Redundant Task: Age Differences Through Network Analyses

There are numerous studies comparing young and old adults in terms of muscle coordination in standard tasks (e.g., walking, reaching) and small variations of them. These tasks might hide differences: individuals would converge to similar behavior as they practice these throughout life. Also, we are unaware of studies that considered the muscle recruitment nested dynamics. For this reason, our study evaluated how young and old women coordinate and control the movement system while performing an unusual redundant motor control task through the network physiology approach. We acquired electromyographic signals from nine leg muscles of the dominant and non-dominant limbs during maximum voluntary isometric contractions (knee extension and flexion) and co-contraction bouts. Our results showed that young participants presented higher peak torque output, with similar EMG variability, compared to older participants. Considering firing rate frequencies, old and young women demonstrated different traits for network clustering and efficiency for the task. Age seems to affect muscle coordination at higher frequencies, even with a similar number of muscle synergies, indicating that younger women might have more integrated synergies than older women. The findings also point to differential muscle coordination adaptability.