Impact of ankle foot orthosis stiffness on Achilles tendon and gastrocnemius function during unimpaired gait

Hwan Choi; Keshia M Peters; Michael B MacConnell; Katie K Ly; Eric S Eckert; Katherine M Steele

doi:10.1016/j.jbiomech.2017.09.015

Impact of ankle foot orthosis stiffness on Achilles tendon and gastrocnemius function during unimpaired gait

J Biomech. 2017 Nov 7:64:145-152. doi: 10.1016/j.jbiomech.2017.09.015. Epub 2017 Sep 23.

Authors

Hwan Choi¹, Keshia M Peters², Michael B MacConnell³, Katie K Ly⁴, Eric S Eckert⁵, Katherine M Steele⁶

Affiliations

¹ Mechanical Engineering, University of Washington, 3900E Stevens Way NE, Box 352600, Seattle, WA 98195, USA. Electronic address: hwanc@uw.edu.
² Mechanical Engineering, University of Washington, 3900E Stevens Way NE, Box 352600, Seattle, WA 98195, USA. Electronic address: rumbek@uw.edu.
³ Mechanical Engineering, University of Washington, 3900E Stevens Way NE, Box 352600, Seattle, WA 98195, USA. Electronic address: mbm87@uw.edu.
⁴ Department of Physics, University of Washington, 3910 15th Ave NE, Box 351560, Seattle, WA 98195, USA. Electronic address: lykatie@uw.edu.
⁵ Human Centered Design & Engineering, University of Washington, 3900E Stevens Way NE, Box 352315, Seattle, WA 98195, USA. Electronic address: eric95@uw.edu.
⁶ Mechanical Engineering, University of Washington, 3900E Stevens Way NE, Box 352600, Seattle, WA 98195, USA. Electronic address: kmsteele@uw.edu.

PMID: 29037441
DOI: 10.1016/j.jbiomech.2017.09.015

Abstract

Ankle foot orthoses (AFOs) are designed to improve gait for individuals with neuromuscular conditions and have also been used to reduce energy costs of walking for unimpaired individuals. AFOs influence joint motion and metabolic cost, but how they impact muscle function remains unclear. This study investigated the impact of different stiffness AFOs on medial gastrocnemius muscle (MG) and Achilles tendon (AT) function during two walking speeds. We performed gait analyses for eight unimpaired individuals. Each individual walked at slow and very slow speeds with a 3D printed AFO with no resistance (free hinge condition) and four levels of ankle dorsiflexion stiffness: 0.25Nm/°, 1Nm/°, 2Nm/°, and 3.7Nm/°. Motion capture, ultrasound, and musculoskeletal modeling were used to quantify MG and AT lengths with each AFO condition. Increasing AFO stiffness increased peak AFO dorsiflexion moment with decreased peak knee extension and peak ankle dorsiflexion angles. Overall musculotendon length and peak AT length decreased, while peak MG length increased with increasing AFO stiffness. Peak MG activity, length, and velocity significantly decreased with slower walking speed. This study provides experimental evidence of the impact of AFO stiffness and walking speed on joint kinematics and musculotendon function. These methods can provide insight to improve AFO designs and optimize musculotendon function for rehabilitation, performance, or other goals.

Keywords: Achilles tendon; Ankle foot orthoses; Gait; Gastrocnemius; Musculoskeletal modeling; Stiffness; Ultrasound.

MeSH terms

Achilles Tendon / physiology*
Adult
Ankle*
Biomechanical Phenomena
Female
Foot Orthoses*
Gait / physiology*
Humans
Male
Muscle, Skeletal / physiology*
Range of Motion, Articular / physiology