Biomechanics, Muscle Activity, and Gait Complexity During Walking With Fatigue-Induced Knee Extensor Impairment

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URL: https://hdl.handle.net/20.500.14394/56315

Abstract

Declines in knee extensor (KE) strength are associated with mobility impairment, risk of knee osteoarthritis (OA), and risk of falls with advancing age. Prior work has attempted to use KE muscle fatigue to study the impact on gait mechanics, however these studies mostly focus on the knee joint and surrounding musculature and often focus only on the sagittal plane or involved only unilateral fatigue. Purpose: The overall aim of this dissertation is to quantify the causal impact of KE muscle strength on age-related alterations in movement patterns using bilateral KE fatigue. We had 3 primary hypotheses: 1) that KE fatigue would shift biomechanics and muscle coordination towards that of aging gait associated with mobility impairment, 2) that KE fatigue will alter 3D knee biomechanics and muscle activity that is consistent with theoretical risk of knee osteoarthritis, and 3) that KE fatigue will change complexity, variability structure, of CoM acceleration during walking consistent with increased risk of falls or pathological gait. Methods: 29 young healthy adults (18F/11M) ages 18-35yrs (23±4.6yrs) performed 2 bilateral KE fatigue protocols where fatigue was quantified as change in maximum isometric torque (MVIC). We compared biomechanics and muscle activity at baseline and after each of the two fatigue protocols where individuals experienced an average decline in MVIC of ~10% and ~20% after each protocol respectively. Results: We found no changes in ankle biomechanics post-fatigue for either protocol. After the second fatigue protocol we found reduced hip and knee range of motion along with reduced propulsion and braking forces, and increased stride frequency all suggesting shorter step lengths. With regard to muscle activity patterns we observed a shift towards more proximal muscle activity paired with a shift towards earlier plantar flexor muscle activity with decreased activity before push off. With the exception of no changes in ankle mechanics these findings are as would be expected with aging gait. With regard to risk of knee OA we found that after the longer fatigue protocol there were changes in femoral translation and rotation relative to the tibia along with more co-activity of the KE and hamstrings through the stance phase of gait. Lastly, we found a decrease in CoM acceleration fractal dimension suggesting reduced complexity and adaptability of gait after the longer KE fatigue protocol. Conclusions: This study was the first of its kind to quantify biomechanics, muscle coordination, co-activation, and activity patterns using two bilateral KE fatigue protocols. We determined that magnitude of fatigue induced when quantified as MVIC is important for whether or not we can detect changes in mechanics. While we did not elicit changes in ankle mechanics we did see changes in muscle activity that may proceed changes in mechanics. We also saw other features of aging gait related to mobility impairment, knee OA, and fall risk suggesting the KE muscles play an important role in declines gait function with age.

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