The Effect of Carbon and Plastic Ankle-Foot Orthoses (AFOS) on Knee Muscle Activity During Varied Walking Conditions

Date of Award

2022

Degree Name

M.S. in Mechanical and Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Kimberly Bigelow

Abstract

Background: Ankle-foot orthoses (AFOs) are external devices that are prescribed for people who were diagnosed with muscle weakness in the lower extremities. These devices are typically prescribed to accommodate the patients for their weak limb(s) by reducing toe-drag and improving ankle dorsiflexion. Previous work has looked at the effects of an AFO on ankle muscle activity during gait. However, there is a lack of information on how AFOs might influence knee muscle activity during gait under different walking conditions. This study examined the effects of a common posterior leaf spring plastic AFO (PAFO) and anterior shell carbon fiber AFO (CAFO) on knee muscle activity in a healthy population during three different treadmill conditions. It was hypothesized that the design of the CAFO, would create less demand on the knee extensors than either the PAFO or no AFO for all walking conditions. Methods: 15 healthy young adults were recruited for this repeated measures study. Noraxon EMG sensors were used to measure the muscle activity of the rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), and semitendinosus (ST) while walking on a treadmill at a comfortable pace. Individuals walked with no AFO, a PAFO and a CAFO during three treadmill conditions (flat, incline, decline). Then, all EMG data were exported to and analyzed using MATLAB, where they were filtered, demeaned, rectified, normalized, and then averaged. Results: Separate one-way ANOVAs were used to identify significant (p<0.05) differences in muscle activity between the AFO conditions during the flat, incline and decline treadmill walking conditions. During flat walking RF, VM and VL muscle activity was significantly lower when using the CAFO compared to both the PAFO and no AFO conditions. During incline walking RF and VM muscle activity was significantly lower when using the CAFO compared to the PAFO and VM and VL muscle activity was significantly lower when using a CAFO compared to no AFO, while BF and ST activity was significantly greater when using a CAFO compared to no AFO. During decline walking, VL muscle activity was significantly greater when using the CAFO compared to no AFO. Conclusions: Muscle activity of the knee extensors (RF, VM and VL) was generally lower when using a CAFO compared to the PAFO or no AFO during both the flat and incline treadmill conditions. These results support our hypothesis that an anterior shell CAFO may be less demanding on knee extensor muscles than a PAFO or no AFO. Conversely, muscle activity of the knee flexors (BF and ST) was higher when using a CAFO compared to no AFO during incline walking but similar to a PAFO. There were no differences in muscle activity between the CAFO and PAFO during the decline treadmill condition. Clinical Relevance: These findings may assist healthcare professionals in proper AFO prescription and rehabilitation, especially for individuals who also display significant knee muscle weakness.

Keywords

Biomechanics, Mechanical Engineering, Physical Education, Philosophy, Physical Therapy, AFO, Ankle foot orthosis, EMG, Electromyography, Knee, Muscles, biomechanics, carbon fiber AFO, Plastic AFO, treadmill, Rectus Femoris, vastus medialis, vastus lateralis, biceps femoris, semitendinosus, physical therapy

Rights Statement

Copyright © 2022, author.

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