Aging effect on muscle synergies in stepping forth during a forward perturbation

Area of Science:

• Neuroscience
• Biomechanics
• Gerontology

Background:

• Healthy aging involves changes in neural control strategies for postural preparation.
• Understanding muscle interactions during aging provides insights into these neural strategies.
• Postural preparation is crucial for maintaining stability during voluntary actions and in response to external perturbations.

Purpose of the Study:

• To investigate age-related changes in multi-muscle synergies during postural preparation.
• To quantify the strength of muscle synergies that stabilize center of pressure (COP) displacement.
• To examine these synergies during preparation for a step in response to support surface translations.

Main Methods:

• Young and elderly participants performed stepping responses to support surface perturbations.
• Surface electromyography of 11 leg and trunk muscles was recorded to identify muscle modes (M-modes).
• Uncontrolled manifold analysis was used to quantify M-mode synergy indices stabilizing COP displacement.

Main Results:

• Elderly subjects showed weaker muscle synergies for stabilizing COP displacement compared to young subjects.
• Synergy indices were significantly lower in older adults prior to step initiation.
• Younger subjects exhibited earlier timing for early postural adjustment (EPA) and anticipatory postural adjustment (APA) than older subjects.

Conclusions:

• Reduced muscle synergy indices with age may challenge postural preparation and stability in older adults.
• This decline could lead to increased muscle co-contraction and reduced COP displacement stability.
• Findings have clinical relevance for identifying fall risk in the elderly, as stepping is linked to falls.