Short communicationQuantifying rearfoot–forefoot coordination in human walking
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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