Effects of the degree of freedom and assistance characteristics of powered ankle-foot orthoses on gait stability

Ho Seon Choi, Yoon Su Baek

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10 Citations (Scopus)


We studied the use of powered ankle-foot orthoses (PAFOs) and walking stability of the wearers, focusing on the ankle joint, which is known to play a critical role in gait stability. Recognizing that the subtalar joint is an important modulator of walking stability, we conducted the walking experiment on a treadmill by applying varying assistance techniques to the 2-degree-of-freedom (DOF) PAFO, which has the subtalar joint as the rotating axis, and the commonly used 1-DOF PAFO. The participants were 8 healthy men (mean±SD: height, 174.8±7.1 cm; weight, 69.8±6.5 kg; and age, 29.1±4.8 years) with no history of gait abnormality. Center of pressure (COP) was measured with an in-shoe pressure sensor, and stability was estimated on the basis of the angular acceleration measured with the inertial measurement unit attached to the trunk. The experimental results of the 2-DOF PAFO, with or without assistance, showed a significantly higher stability than those of the 1-DOF PAFO (up to 23.78%, p<0.0326). With the 1-DOF PAFO, the stability deteriorated with the increase in the degree of assistance provided. With the 2-DOF PAFO, this tendency was not observed. Thus, the importance of the subtalar joint was proven using PAFOs. The mean position analysis of the COP during the stance phase confirmed that the COP highly correlated with stability (Pearson correlation coefficient: −0.6607). Thus, we conclude that only the 2-DOF PAFO can maintain walking stability, regardless of the assistance characteristics, by preserving the COP in the medial position through eversion. Awareness regarding the role of the subtalar joint is necessary during the manufacture or use of PAFOs, as lack of awareness could lead to the degradation of the wearer’s gait stability, regardless of effective assistance, and deteriorate the fundamental functionality of PAFO.

Original languageEnglish
Article numbere0242000
JournalPloS one
Issue number11 November
Publication statusPublished - 2020 Nov

Bibliographical note

Publisher Copyright:
© 2020 Choi, Baek. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

All Science Journal Classification (ASJC) codes

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)
  • General


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