Aging effects on the Achilles tendon moment arm during walking

Area of Science:

• Biomechanics
• Gerontology
• Musculoskeletal physiology

Background:

• The Achilles tendon (AT) moment arm is crucial for ankle propulsion during walking.
• This moment arm is dynamic, influenced by joint angle and muscle loading.
• Aging is associated with reduced ankle power during walking, but the underlying AT mechanics are unclear.

Purpose of the Study:

• To investigate how aging affects the Achilles tendon moment arm during walking.
• To determine the relationship between AT moment arm, muscle loading, and ankle moment generation in young and older adults.
• To explore age-related differences in the load-dependent modulation of the AT moment arm.

Main Methods:

• Utilized motion capture and ultrasound imaging to quantify AT moment arm variations.
• Compared young (23.9 ± 4.3 years) and older (69.9 ± 2.6 years) adults during walking.
• Assessed the dependence of the AT moment arm on triceps surae muscle loading and its correlation with ankle push-off moments.

Main Results:

• Older adults exhibited an 11% smaller AT moment arm and 11% smaller peak ankle moments during push-off compared to young adults.
• A significant positive correlation (r² = 0.38, p < 0.01) was found between AT moment arm size and peak ankle moments.
• Aging attenuated the increase in AT moment arm with muscle loading; only young adults showed a significant load-dependent increase.

Conclusions:

• Age-related reductions in AT moment arm compromise ankle propulsion during walking.
• Decreased triceps surae muscle volume or activation in older adults may reduce muscle bulging, diminishing the AT's mechanical advantage.
• Interventions to enhance locomotor function in aging populations should address these musculoskeletal changes affecting the AT moment arm.