The nature of functional variability in plantar pressure during a range of controlled walking speeds

Abstract

During walking, variability in step parameters allows the body to adapt to changes in substrate or unexpected perturbations that may occur as the feet interface with the environment. Despite a rich literature describing biomechanical variability in step parameters, there are as yet no studies that consider variability at the body–environment interface. Here, we used pedobarographic statistical parametric mapping (pSPM) and two standard measures of variability, mean square error (m.s.e.) and the coefficient of variation (CV), to assess the magnitude and spatial variability in plantar pressure across a range of controlled walking speeds. Results by reduced major axis, and pSPM regression, revealed no consistent linear relationship between m.s.e. and speed or m.s.e. and Froude number. A positive linear relationship, however, was found between CV and walking speed and CV and Froude number. The spatial distribution of variability was highly disparate when assessed by m.s.e. and CV: relatively high variability was consistently confined to the medial and lateral forefoot when measured by m.s.e., while the forefoot and heel show high variability when measured by CV. In absolute terms, variability by CV was universally low (less than 2.5%). From these results, we determined that variability as assessed by m.s.e. is independent of speed, but dependent on speed when assessed by CV.

Intra-subject sample size effects in plantar pressure analyses

“…They provide key insights into the modulation of foot function (e.g., Simpson et al, 1993;Maluf & Mueller, 2003;Stepháne 2008;Caravaggi, Leardini & Giacomozzi, 2016;Taş & Çetin, 2019), in addition to delivering fundamental insights into the evolution of hominid foot morphology and function (e.g., Vereecke et al, 2003;Crompton et al, 2012;Bates et al, 2013a;Bates et al, 2013b;DeSilva & Gill, 2013;McClymont & Crompton, 2021). Recent work using large intra-subject human datasets (>500 steps per subject) identified high levels of both inter-(i.e., between individuals) and intra-subject (i.e., within subjects step-to-step) variance in peak plantar pressure in the midfoot (Bates et al, 2013a), and across the whole plantar surface in healthy adults (McClymont et al, 2016). This is qualitatively consistent with earlier work measuring variability in loading patterns of neuropathic patients from sample sizes of >50 pressure records (Cavanagh et al, 1998).…”

Repetition Without Repetition: A Comparison of the Laetoli G1, Ileret, Namibian Holocene and Modern Human Footprints Using Pedobarographic Statistical Parametric Mapping

“…Wolf et al 2008), both natural and essential components to be considered in analyses of fossil footprint trails and explaining the difference between prints and between populations via high variability. Figure 3.2 represents all prints in the Laetoli G1 sample used in this analysis alongside 11 consecutive p-images collected during treadmill walking from a healthy human at 1.1 m/s (McClymont et al 2016). This figure is not a statistical comparison of relative depths (Laetoli) and plantar pressures (modern human) as the two samples were collected under completely different conditions.…”

“…Sample sizes of as little as 10, and at most 50, are commonly used to assess gait parameters including pressure and kinematics in clinical practice. The higher value of 50 slightly mitigates the effect of step-to-step variability that would otherwise perhaps lead to false interpretations, due to the high variability step-to-step (McClymont et al 2016). Owings and Grabiner (2003) however have demonstrated that sample sizes of over 100 steps are needed to reliably characterize an individual's kinematics, to within 95% confidence.…”

Combining F-Scan and GAITRite® for use in Clinical Gait Analysis: A Validation Study.

“…Kong & De Heer [25] suggest that such ranges of differences are small, taking into consideration the natural variability of gait and the varied repeatability of plantar pressure. Research analysing the variability of plantar pressure at controlled speeds suggests that this variability can be a result of the speed at which a person walks [26]. Other studies have suggested that the natural variability of an individual's gait could account for the frequently poor repeatability results exhibited by F-Scan [27].…”