Elsevier

Journal of Biomechanics

Volume 41, Issue 14, 20 October 2008, Pages 3101-3105
Journal of Biomechanics

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Quantifying rearfoot–forefoot coordination in human walking

https://doi.org/10.1016/j.jbiomech.2008.07.024Get rights and content

Abstract

A method is proposed to facilitate the quantification and interpretation of inter-joint/-segment coordination. This technique is illustrated using rearfoot–forefoot kinematic data. We expand existing vector coding techniques and introduce a set of operational terms through which the coordinative patterns between the rearfoot segment and the forefoot segment are summarized: in-phase, anti-phase, rearfoot phase and forefoot phase. The literature on foot mechanics has characterized the stable foot at pushoff by a decreasing medial longitudinal arch angle in the sagittal plane, which is accompanied by forefoot pronation and concurrent rearfoot supination—in other words, anti-phase motion. Nine skin markers were placed on the rearfoot and forefoot segments according to a multi-segment foot model. Three healthy subjects performed standing calibration and walking trials (1.35 m s−1), while a three-dimensional motion capture system acquired their kinematics. Rearfoot–forefoot joint angles were derived and the arch angle was inferred from the sagittal plane. Coupling angles of rearfoot and forefoot segments were derived and categorized into one of the four coordination patterns. Arch kinematics were consistent with the literature; in stance, the arch angle reached peak dorsiflexion, and then decreased rapidly. However, anti-phase coordination was not the predominant pattern during mid- or late stance. These preliminary data suggest that the coordinative interactions between the rearfoot and the forefoot are more complicated than previously described. The technique offers a new perspective on coordination and may provide insight into deformations of underlying tissues, such as the plantar fascia.

Introduction

The goal of this paper is to facilitate the quantification and interpretation of inter-segment/-joint coordination. Coordinative patterns are usually inferred from angle–time plots. However, when kinematics of a segment or joint couple need to be considered simultaneously, side-by-side angle–time plots fail to quantify inter-segment/-joint coordinative relationships. Therefore, we expand existing vector coding techniques of angle–angle diagrams (Sparrow et al., 1987) to quantify inter-segment/-joint coordination. In doing so, coordination patterns may be presented in time series, so that readers can easily visualize their evolution. Furthermore, we introduce a relatively simple set of operational terms through which coordination patterns are summarized: in-phase, anti-phase, proximal phase and distal phase.

We will illustrate this new method using rearfoot–forefoot kinematic data. A body of literature on rearfoot–forefoot coordination consists mainly of cadaver models and results from clinical experience. Quantification of rearfoot–forefoot coordination enables hypotheses from the literature to be examined in greater detail. For example, the notion of the stable/unstable (or high-/low-gear) pushoff can be more thoroughly examined. At pushoff, a stable foot is characterized by a decreasing medial longitudinal arch angle in the sagittal plane, and coordinated forefoot pronation and rearfoot supination (Elftman, 1960; Bojsen-Moller, 1979)—in other words, anti-phase motion.

Section snippets

Methods

Three healthy subjects gave written consent to participate: two males, one female (mean±SD: age: 27.7±1.2, BMI: 23.0±2.5; arch index (Williams and McClay, 2000): 0.320±0.018). The subjects had no history of foot/leg problems.

Nine retro-reflective markers (diameter 8.0 mm) were placed on the skin of the right rearfoot and forefoot according to a multi-segment foot model (Leardini et al., 2007). Kinematic and kinetic data were collected synchronously for standing calibration and straight-line

Results

Typical rearfoot–forefoot joint angle–time series indicated a peak in forefoot dorsiflexion with respect to the rearfoot at 73% stance, followed by rapid plantar flexion (Fig. 2a). The frontal and transverse joint angle–time series exhibited a trough and valley shape starting with forefoot eversion and abduction (Fig. 2b and c). Stance finished with forefoot inversion and adduction.

Segmental angle–angle and coupling angle–time graphs provide more detail on inter-segmental coordination (Fig. 3).

Discussion

In an effort to quantify inter-segment/-joint coordination, we expanded a vector coding method. Qualitative assessments of rearfoot–forefoot segmental coordination have been the mainstay of foot mechanics literature. Intrinsic foot kinematics were acquired and these agreed with previous reports (Pohl and Buckley, 2008; Leardini et al., 2007; Rao et al., 2007). Segment angles were vector coded, averaged with circular statistics, and coordination was reported according to defined patterns.

Conflict of interest

None.

Acknowledgments

RC acknowledges the International Society of Biomechanics Dissertation Grant. We thank Ross H. Miller for editorial contribution.

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