Doctoral Examination: Contribution of muscle-tendon mechanics to force control

Rowan Smart, supervised by Dr. Jennifer Jakobi, will defend their dissertation titled “Contribution of muscle-tendon mechanics to force control” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Kinesiology.

An abstract for Rowan’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

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ABSTRACT

The overall goal of this dissertation is to evaluate contributions of muscle and tendon behavior to isometric force control and balance tasks. This was undertaken in populations that have well-established differences in muscle-tendon mechanics, force steadiness (FS), and balance. The specific objectives of this dissertation were as follows: 1) Determine if using resting tendon cross-section area (CSA) underestimates tendon stress compared to using CSA measured during contraction in the calculation, 2) Assess the contribution of muscle-tendon mechanics to population-based differences in FS, and 3) Examine intermuscular coherence during standing balance in a population with reduced balance. Study #1 addressed objective 1 by demonstrating that tendon stress values of the distal biceps brachii (BB) tendon are significantly greater when using measures of CSA obtained during contraction compared to at rest, and that the differential increase between methods in calculated stress values is both sex- and age-dependent. Study #2 addressed objective 2 by examining contributions of distal BB tendon mechanics to isometric elbow flexion FS in young males and females, and showed that greater strength and tendon stress in males facilitates the production of steadier elbow flexion compared to females. Study #3 also addressed objective 2 and demonstrated that lower strength in older adults with Parkinson’s disease (PD) contributes to reduced plantarflexion FS compared to age- and sex-matched healthy older adults, and that reduced medial gastrocnemius fascicle shortening and Achilles tendon elongation in PD may also be a contributing factor. Study #4 addressed objective 3 by evaluating intermuscular coherence of the plantar flexors along with center of pressure (CoP) parameters during standing balance in older adults with PD and age- and sex-matched healthy older adults. Older adults with PD had marginal increases in CoP parameters, but intermuscular coherence did not differ between groups, suggesting that lower-leg intermuscular coherence is not a contributing factor to increased sway in high-functioning older adults with PD. This dissertation provides new insight as to the contribution of muscle-tendon mechanics and muscle coordination to functional force control through sex-, age- and disease-based population comparatives, and demonstrates the importance of tendon mechanics in producing steady contractions.