Effector-dependent decline in strength and subcortical motor excitability with aging

Area of Science:

• Neuroscience
• Gerontology
• Human Physiology

Background:

• Upper limb strength commonly declines with aging.
• The relationship between age-related strength loss and descending motor pathway excitability remains unclear.
• The reticulospinal tract is crucial for gross motor control and its excitability can be modulated by training.

Purpose of the Study:

• To investigate age-related changes in upper limb strength.
• To assess age-related alterations in reticulospinal tract excitability.
• To determine if reduced reticulospinal excitability contributes to age-related strength decline in upper limb flexors and extensors.

Main Methods:

• Quantified upper limb strength using dynamometry in younger and older adults.
• Assessed reticulospinal tract excitability via transcranial magnetic stimulation to elicit ipsilateral motor evoked potentials.
• Compared strength and motor pathway excitability between age groups.

Main Results:

• Older adults exhibited reduced flexion strength compared to younger adults, but extension strength was not significantly different.
• A decrease in the presence of ipsilateral motor evoked potentials was observed in older adults, specifically for flexor muscles.
• The observed decline in flexion strength correlated with reduced reticulospinal tract excitability in older individuals.

Conclusions:

• Reduced excitability of the reticulospinal tract may be a significant factor in the age-related decline of upper limb strength, particularly in flexor muscles.
• The reticulospinal tract, with its prominent innervation of flexor muscles, appears to be differentially affected by aging.
• These findings provide insights into the neural mechanisms underlying age-associated motor impairments in the upper limbs.