Adaptation of a Dynamic Muscle Mechanics Model to Simulate Movement in Young and Old Adults

Abstract

The project I participated in involved the development of a direct-dynamics model to realistically simulate human movement. The model consisted of a multi-segmented representation of the body with Hill-type musculo-tendon actuators across the joints to accurately reproduce muscle power and torque. My exclusive role was to help validate/improve the model by generating simulations and comparing them with experimental data obtained from human subjects during strength exercises. Through my adjustments to muscle characteristics of the model, I was able to closely reproduce the joint torque vs. joint angle curves created across the hip joint during specific movements. The model parameters of the Hill-type musculo-tendon model were then adjusted to reflect changes in muscle mechanics that occur with aging. Adapting the muscle model for older adults (-70 years old) involved: 1) Decreasing muscle cross-sectional areas, maximum stress capability of the muscle, and maximum contraction velocity; 2) Slowing muscular deactivation; 3) Increasing the relative force capacity during lengthening contractions. The resulting model predicted diminished hip strength, power development, and slowed torque development that were in agreement with experimental observations of healthy older adults. This musculo-tendon model can then be used in direct-dynamics simulations to predict how age-related changes in muscle may impact the abilities of old adults to perform tasks requiring rapid movements and/or substantial strength.