Task difficulty and limb dominance modulate the effects of ageing on neuromuscular function.

Area of Science:

• Neurology
• Gerontology
• Motor Control

Background:

• Neuromuscular function is vital for maintaining independence in aging adults.
• Limb asymmetries in neuromuscular function can arise from central or peripheral factors, but are not well understood.
• Age-related changes in motor unit (MU) behavior and force control are critical for mobility.

Purpose of the Study:

• To investigate age- and limb-related differences in neuromuscular function.
• To analyze motor unit firing behavior in the vastus lateralis muscle during tasks of varying difficulty.
• To understand how task difficulty influences limb asymmetries in neuromuscular control during aging.

Main Methods:

• Recruited young and older adults for unilateral isometric knee extension tasks (constant and variable force).
• Utilized high-density surface electromyography to decompose signals into MU spike trains.
• Applied multilevel mixed-effects regression models to analyze force control and MU firing properties.

Main Results:

• Older adults exhibited reduced maximal muscle strength and increased force tracking error compared to younger adults.
• No significant limb-specific differences in muscle strength or force control were observed within age groups.
• Motor unit firing rate (MUFR) was lower in older adults, and MUFR variability showed a significant interaction with leg dominance and age group.
• Older adults displayed greater MUFR variability in non-dominant legs, while younger adults showed the opposite, particularly under variable force conditions.

Conclusions:

• Neuromuscular aging is characterized by asymmetric adaptations rather than a uniform decline.
• Limb dominance effects on neuromuscular control become more pronounced with increased task difficulty, especially during variable force modulation.
• Future age-related motor assessments should consider limb-specific neural control mechanisms to accurately evaluate functional capacity.