# The Role of Muscle Dynamics in Governing Achilles Subtendon Behavior Across the Lifespan

> **NIH NIH F31** · UNIV OF NORTH CAROLINA CHAPEL HILL · 2020 · $21,632

## Abstract

Project Summary
In young adults, the positive mechanical power generated via triceps surae (i.e., gastrocnemius -GAS, soleus-
SOL) muscle-tendon interaction is responsible for a large majority of the total power needed to walk. Recent
evidence suggests that GAS and SOL transmit their forces through distinct, and perhaps mechanically
independent, subtendons that merge and twist to form the Achilles tendon (AT). Consistent with our preliminary
ultrasound imaging results in humans, animal models of the aging AT allude to adhesions between adjacent
subtendons. We propose that these adhesions unfavorably couple the GAS and SOL, thereby negatively affecting
fundamental mechanisms that influence muscle-subtendon interaction dynamics and triceps surae mechanical
output during walking. Using a novel dual-probe imaging technique, our preliminary data reveal that triceps
surae muscle dynamics may precipitate non-uniform displacement patterns in the architecturally complex AT of
young adults, thereby facilitating mechanical independence of GAS (responsible for forward propulsion) and
SOL (responsible for trunk support). Aim 1: Our proposal will leverage our novel dual-probe imaging technique
to determine the role of muscle contractile dynamics in governing localized AT tissue displacements in young
adults. Aim 2: We will then quantify the effects of aging on the role of muscle contractile dynamics in governing
Achilles subtendon displacement (and vice versa). Aim 3: Finally, we will integrate our measured muscle-
subtendon interaction dynamics into a computational model of the lower extremity to identify mechanistic causal
relations between relevant architectural and neuromuscular factors in precipitating age-related changes during
walking. The findings from this study will have immediate impact on our understanding of musculoskeletal
mechanisms underlying age-related mobility impairment toward improving the health and welfare of our aging
population. Moreover, our technological advancements in musculoskeletal imaging will revolutionize the use of
in vivo ultrasound during functional locomotor behavior, with broad implications in humans and other animals.
More broadly, the knowledge gained from this study could significantly accelerate the development of engineered
tissues, regenerative medicine approaches and therapies, and orthopaedic surgical intervention.

## Key facts

- **NIH application ID:** 9972735
- **Project number:** 5F31AG060675-02
- **Recipient organization:** UNIV OF NORTH CAROLINA CHAPEL HILL
- **Principal Investigator:** William H Clark
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $21,632
- **Award type:** 5
- **Project period:** 2019-07-01 → 2020-12-13

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9972735

## Citation

> US National Institutes of Health, RePORTER application 9972735, The Role of Muscle Dynamics in Governing Achilles Subtendon Behavior Across the Lifespan (5F31AG060675-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9972735. Licensed CC0.

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