A Non-Invasive Approach for Studying Muscle-Tendon In-vivo

University Of California-Davis, Davis CA

Investigators

Abstract

0201829 Hawkins Muscle-tendon units are complex biological actuators able to impart considerable force to bones to stabilize and/or move segments of the body and to absorb energy imparted to the body. Due to the integral role muscle-tendon (MT) units play in human function and quality of life, considerable interest exists in understanding 1) the basic structural properties of MT units, 2) how MT properties change throughout life and in response to altered environmental stimuli (e.g. disuse, exercise), 3) risk factors associated with MT injury, 4) how best to maintain or restore normal MT function throughout life, and 5) how to compensate for a loss in MT function. Difficulty in quantifying the structural properties of muscle-tendon units in-vivo has limited understanding of the normal and adaptive behavior of these units. The two objectives of this study are: 1) to develop a methodology to non-invasively quantify muscle and tendon force-deformation properties in-vivo, and 2) to demonstrate the utility of this approach by using it to investigate two specific questions (a) are there age-related differences in the strain induced in a tendon during a maximum isometric muscle contraction performed by people of similar physical activity level, and (b) are there age-related differences in the rate of structural property adaptation of a tendon relative to the rate of muscle strength adaptation in people of similar initial physical activity level? A methodology that combines ultrasonography, a force transducer, and an ankle-testing fixture is being developed to study the Gastrocnemius-Soleus-Achilles Tendon Complex, which provide the primary forces to plantar flex the ankle. The ultrasound images will be used to quantify the length and cross-sectional area of the Achilles Tendon, muscle fascicle orientation, and movement of anatomical landmarks during muscle contractions or joint movements. The ankle-testing device will be used to quantify ankle position and torque for a given muscle effort. Anthropometric data will be used to relate joint torque to Achilles Tendon force. Force-deformation and stress-strain behaviors of the tendon are quantified. The validity of these methods will be tested using instrumented cadaver specimens. Tissue force and/or deformation will be controlled within the cadaver leg and compared to similar quantities determined from the non-invasive ultrasound and joint testing procedures. The utility of the non-invasive technique for studying basic muscle-tendon performance and adaptation will be investigated by studying the affects that aging and exercise have on MT behavior and joint mechanics. Twenty-five subjects within three age groups will participate in a 16-week strength-training program and an 8-week detraining program. Every two weeks the subjects will perform gradually increasing isometric plantar flexion efforts while Achilles tendon force and deformation are recorded. These data will be used to construct force-deformation curves for the tendon and to quantify tendon stiffness, maximum isometric muscle strength, and tendon strain during maximum isometric muscle force. Additionally, electromyography from the soleus and gastrocnemius muscles will be recorded to quantify muscle recruitment strategies during these muscular efforts. Data will be compared between subjects, test sessions, and age groups.