Elsevier

Journal of Biomechanics

Volume 75, 25 June 2018, Pages 1-12
Journal of Biomechanics

Review
Ankle and foot power in gait analysis: Implications for science, technology and clinical assessment

https://doi.org/10.1016/j.jbiomech.2018.04.017Get rights and content

Abstract

In human gait analysis studies, the entire foot is typically modeled as a single rigid-body segment; however, this neglects power generated/absorbed within the foot. Here we show how treating the entire foot as a rigid body can lead to misunderstandings related to (biological and prosthetic) foot function, and distort our understanding of ankle and muscle-tendon dynamics. We overview various (unconventional) inverse dynamics methods for estimating foot power, partitioning ankle vs. foot contributions, and computing combined anklefoot power. We present two case study examples. The first exemplifies how modeling the foot as a single rigid-body segment causes us to overestimate (and overvalue) muscle-tendon power generated about the biological ankle (in this study by up to 77%), and to misestimate (and misinform on) foot contributions; corroborating findings from previous multi-segment foot modeling studies. The second case study involved an individual with transtibial amputation walking on 8 different prosthetic feet. The results exemplify how assuming a rigid foot can skew comparisons between biological and prosthetic limbs, and lead to incorrect conclusions when comparing different prostheses/interventions. Based on analytical derivations, empirical findings and prior literature we recommend against computing conventional ankle power (between shank-foot). Instead, we recommend using an alternative estimate of power generated about the ankle joint complex (between shank-calcaneus) in conjunction with an estimate of foot power (between calcaneus-ground); or using a combined anklefoot power calculation. We conclude that treating the entire foot as a rigid-body segment is often inappropriate and ill-advised. Including foot power in biomechanical gait analysis is necessary to enhance scientific conclusions, clinical evaluations and technology development.

Introduction

Muscles and tendons about the ankle, knee and hip are typically considered the main mechanical power producers during human gait. Using inverse dynamics to estimate net power generated about these joints has become ubiquitous in human gait analysis studies (Robertson et al., 2013, Winter, 2009, Winter, 1991). Substantial effort has gone into characterizing how ankle, knee and hip kinetics are adapted during different locomotor tasks and varying task intensities (e.g., Farris and Sawicki, 2012a, Winter, 1984, Winter, 1983, Zelik and Kuo, 2010), and understanding how power about each of these three joints contributes functionally to movement biomechanics (e.g., Mann and Hagy, 1980, Inman et al., 1981, Perry, 1992, Levine et al., 2012, Zelik and Adamczyk, 2016). However, in gait analysis studies, far less attention has been given to power contributions from the foot.

Foot power, the rate of mechanical work performed collectively by active and passive structures of the foot (sometimes including the shoe), is not typically estimated in gait analysis studies (Zelik et al., 2015). The standard convention in the gait analysis field is to model the entire foot as a single rigid-body segment, which neither absorbs nor generates mechanical power. This convention is found throughout biomechanics textbooks (Baker, 2013, Inman et al., 1981, Rancho Los Amigos National Rehabilitation Center, 2001, Robertson et al., 2013, Whittle, 2014, Winter, 2009), and is reflected in commonly-used motion capture marker sets. However, there is compelling evidence that foot power contributes meaningfully to walking (Bruening et al., 2012a, MacWilliams et al., 2003, Siegel et al., 1996, Takahashi et al., 2012, Takahashi and Stanhope, 2013, Zelik et al., 2015) and running (Kelly et al., 2015, McDonald et al., 2016, Riddick and Kuo, 2016, Stearne et al., 2016, Stefanyshyn and Nigg, 1997), due to a complex biomechanical interplay between muscles and passive structures (Kelly et al., 2014, Ker et al., 1987, Venkadesan et al., 2017, Zelik et al., 2014).

Currently there remains a lack of clarity in the scientific literature regarding if, when and how foot power should be calculated in the study of gait biomechanics. A critical question looms: is modeling the entire foot as one rigid-body segment, which neither absorbs nor generates mechanical power, adequate for addressing the types of the scientific questions that are commonly investigated in gait analysis studies, or adequate for obtaining biomechanical estimates that properly inform the design, prescription and evaluation of clinical interventions (e.g., foot prostheses)? Here we present experimental evidence and analytical arguments suggesting that, in many cases, neglecting foot power is inadequate for scientific studies and may be inappropriate (misleading) for clinical gait analysis or informing technology development.

The purpose of this article is two-fold: (i) to use case study examples in conjunction with analytical arguments and prior literature to highlight why foot power should be estimated within the context of whole-body or lower-limb gait analysis studies, and then (ii) to discuss how to experimentally estimate (and interpret) foot and ankle power. This article is principally intended for individuals who employ conventional gait analysis methods (e.g., 3 degree-of-freedom (3DOF) rigid-body inverse dynamics) to understand bio- or neuro-mechanical aspects of human locomotion, to inform device design, or to evaluate clinical interventions. Some of the observations contained within this article may be banal or obvious to foot experts and enthusiasts. But if so, this is all the more reason to resolve the discontinuity between scientists, engineers and clinicians focused specifically on the foot, and those who use gait analysis methods such as inverse dynamics to more broadly investigate how constituents of the body (e.g., individual joints, segments, muscles or tendons) contribute to whole-body movement.

Section snippets

Methods

We performed two gait analysis case studies that exemplify how and why to compute foot power, and implications on ankle power. The first case study was on a healthy individual during treadmill walking at fixed speed. We used an extended marker set to compute and contrast various estimates of ankle power, foot power, and combined ankle plus foot (termed anklefoot) power. The second case study involved a person with unilateral transtibial amputation walking sequentially on eight different

Case study 1

Ankle power estimates were similar with both 3DOF and 6DOF methods in terms of peak power and positive work (Fig. 3). These findings are consistent with prior studies, each on 10 subjects (Buczek et al., 1994, Zelik et al., 2015). Anklefoot power estimates were also similar to each other (Fig. 3). This result is consistent with Takahashi et al. (2012), who previously demonstrated strong similarity between Distal Shank power and Ankle+Distal Foot power. However, Ankle power and positive work

Discussion

These case studies exemplify problems that can arise when the entire foot is treated as a single rigid-body segment. Below we discuss scientific, clinical and technological implications, which highlight why it is important to include foot power in gait analysis studies; either explicitly by computing it, or implicitly by taking the (non-rigid) anatomy of the foot into account when estimating power about the ankle. Based on these empirical examples, analytical arguments and corroborating

Conclusion

Treating the entire foot as a single rigid-body segment can result in obscuring (or even completely missing) important dynamics, re-affirming conclusions from prior multi-segment foot modeling studies. Here we overview why this is important to the gait analysis community, and how to better estimate anklefoot dynamics experimentally. Specifically, we highlight how neglecting foot power can hinder our scientific understanding of movement, confound our ability to make robust clinical comparisons

Conflict of interest

The authors have no conflict of interest to declare.

Acknowledgements

This work was supported by funding from the National Institutes of Health (K12HD073945) and from the National Science Foundation (CBET – 1605200). We gratefully acknowledge New Balance for donating footwear. We would like to thank Erik Lamers for his help with data collection and processing. And we would like to thank a host of colleagues – notably, Matthew Yandell, Kota Takahashi, Luke Kelly, Thomas Kepple, Maura Eveld and Harrison Bartlett – for their thought-provoking discussions and helpful

References (72)

  • M.D. Geil et al.

    Comparison of methods for the calculation of energy storage and return in a dynamic elastic response prosthesis

    J. Biomech.

    (2000)
  • A. Leardini et al.

    Rear-foot, mid-foot and fore-foot motion during the stance phase of gait

    Gait Posture

    (2007)
  • B.A. MacWilliams et al.

    Foot kinematics and kinetics during adolescent gait

    Gait Posture

    (2003)
  • D.C. Morgenroth et al.

    The effect of prosthetic foot push-off on mechanical loading associated with knee osteoarthritis in lower extremity amputees

    Gait Posture

    (2011)
  • R.R. Neptune et al.

    Contributions of the individual ankle plantar flexors to support, forward progression and swing initiation during walking

    J. Biomech.

    (2001)
  • C. Nester et al.

    Foot kinematics during walking measured using bone and surface mounted markers

    J. Biomech.

    (2007)
  • C. Reinschmidt et al.

    Tibiofemoral and tibiocalcaneal motion during walking: external vs. skeletal markers

    Gait Posture

    (1997)
  • R.C. Riddick et al.

    Soft tissues store and return mechanical energy in human running

    J. Biomech.

    (2016)
  • A. Sawers et al.

    Trajectory of the center of rotation in non-articulated energy storage and return prosthetic feet

    J. Biomech.

    (2011)
  • S.H. Scott et al.

    Biomechanical model of the human foot: Kinematics and kinetics during the stance phase of walking

    J. Biomech.

    (1993)
  • K.L. Siegel et al.

    Improved agreement of foot segmental power and rate of energy change during gait: Inclusion of distal power terms and use of three-dimensional models

    J. Biomech.

    (1996)
  • J. Stebbins et al.

    Repeatability of a model for measuring multi-segment foot kinematics in children

    Gait Posture

    (2006)
  • D.J. Stefanyshyn et al.

    Mechanical energy contribution of the metatarsophalangeal joint to running and sprinting

    J. Biomech.

    (1997)
  • K.Z. Takahashi et al.

    A unified deformable (UD) segment model for quantifying total power of anatomical and prosthetic below-knee structures during stance in gait

    J. Biomech.

    (2012)
  • J.C. Wager et al.

    Elastic energy within the human plantar aponeurosis contributes to arch shortening during the push-off phase of running

    J. Biomech.

    (2016)
  • D.A. Winter

    Kinematic and kinetic patterns in human gait: Variability and compensating effects

    Hum. Mov. Sci.

    (1984)
  • G. Wu et al.

    ISB recommendation on definitions of joint coordinate system of various joints for the reporting of human joint motion—part I: ankle, hip, and spine

    J. Biomech.

    (2002)
  • E.S. Arch et al.

    Combined Ankle-Foot Energetics are Conserved When Distal Foot Energy Absorption is Minimized

    J. Appl. Biomech.

    (2016)
  • R.W. Baker

    Measuring Walking: A Handbook of Clinical Gait Analysis

    (2013)
  • R.A. Bogey et al.

    An EMG-to-force processing approach for determining ankle muscle forces during normal human gait

    IEEE Trans. Neural Syst. Rehabil. Eng.

    (2005)
  • S.H. Collins et al.

    Recycling energy to restore impaired ankle function during human walking

    PLoS One

    (2010)
  • A. Crimin et al.

    The effect that energy storage and return feet have on the propulsion of the body: A pilot study

    Proc. Inst. Mech. Eng.

    (2014)
  • A.R. De Asha et al.

    Walking speed related joint kinetic alterations in trans-tibial amputees: impact of hydraulic 'ankle’ damping

    J. NeuroEng. Rehabil.

    (2013)
  • D.J. Farris et al.

    The mechanics and energetics of human walking and running: a joint level perspective

    J. R. Soc. Interface

    (2012)
  • D.J. Farris et al.

    Human medial gastrocnemius force–velocity behavior shifts with locomotion speed and gait

    Proc. Natl. Acad. Sci.

    (2012)
  • A.L. Hof et al.

    Calf muscle work and segment energy changes in human treadmill walking

    J. Electromyogr. Kinesiol.

    (1993)
  • Cited by (117)

    • Unveiling Patterns and Abnormalities of Human Gait: A Comprehensive Study

      2024, Indian Journal of Information Sources and Services
    View all citing articles on Scopus
    View full text