The influence of walking speed on plantar pressure measurements using the two-step gait initiation protocol

Abstract

Background: Plantar pressure measurement is being increasingly used in both research and clinical practice to measure the effects of various footwear and physical therapy interventions. However, the influence of walking speed on plantar pressure parameters has not been evaluated in detail, and may have an effect on study design and interpretation of results.

Objective: To determine the effect of changes in walking speed on plantar pressure measurements obtained using the two-step gait initiation protocol.

Methods: Plantar pressure parameters were measured with the EMED-SF system using the two-step gait initiation protocol in 20 healthy participants (10 males, 10 females) aged 20–37 (mean 27.5, S.D. 5.2 years) when walking at self-selected slow, normal and fast speeds.

Results: With increased walking speeds, contact time increased at all regions under the foot. When expressed as a percentage of stance phase, contact time at the forefoot was not affected by walking speed; however, a smaller proportion of stance phase was spent loading the medial and lateral heel and lateral midfoot regions. Maximum force and peak pressure consistently increased at all regions at faster walking speeds, with the exception of the lateral midfoot, first MPJ and third–fifth MPJ regions. Force–time and pressure–time integrals were reduced at faster walking speeds, with the exception of loading under the toes, which remained relatively constant.

Conclusions: Variations in walking speed from slow to fast significantly influence the timing and magnitude of plantar pressure values using the two-step gait initiation protocol. However, no significant differences are evident between self-selected slow and normal speeds for maximum force and peak pressure values. These findings suggest that when assessing the effects of various interventions on plantar pressure patterns, correcting for small changes in walking speed at slower speeds may not be critical for maximum force and peak pressure measurements, but is necessary for appropriate interpretation of force–time and pressure–time integrals at most regions of the plantar foot.

Introduction

Plantar pressure measurement is being increasingly used in both research and clinical practice to compare gait patterns of different clinical groups and to evaluate the effects of footwear, orthotic and surgical interventions [1]. Significant differences in pressure patterns have been reported in people with diabetic neuropathy [2], [3], [4], leprosy [5] and rheumatoid arthritis [6] compared to healthy subjects, and numerous studies have employed plantar pressure technology to demonstrate significant changes in foot function when wearing orthoses [7], [8], [9], [10]. However, as with any technique for assessing gait patterns, it is important to determine whether the changes observed truly reflect the disease process or intervention being studied, rather than simply reflecting between-subject or between-trial variations in walking speed. This can be achieved either by standardising walking speed between trials (by the use of treadmills or metronomes), or by requesting subjects to walk at their normal speed and correcting for differences between subjects prior to undertaking inferential analyses. The former approach is limited due to changes in gait patterns induced by treadmills [11], [12], [13] and the difficulty some people have in walking to the beat of a metronome. The latter approach allows subjects to be assessed when walking normally, but requires an understanding of the relationship between walking speed and the parameters being studied. Indeed, concern has been expressed as to the impact of walking velocity on kinetic and kinematic parameters of gait. Lelas et al. [14] investigated the effect of self-determined walking speeds using staggered force platforms and concluded that there was a predictable change in force with altered walking velocities.

Despite the widespread use of plantar pressure technology, only three studies have directly addressed the influence of walking speed on pressure parameters. Using the EMED-F pressure plate system, Hughes et al. [15] reported linear increases in force and pressure values under the whole foot when participants walked at slow, medium and fast cadences. However, not all regions of the foot were equally influenced by speed, with the heel exhibiting increases in maximum force and peak pressure, while the lateral midfoot, lateral forefoot and lateral toes either showing no change or decreases in loading. Rosenbaum et al. [16] reported similar findings in 30 healthy participants using the EMED-SF2 system, and interpreted the changes in loading patterns as representing an overall medial shift in pressure. Finally, Zhu et al. [17] measured in-shoe plantar pressures in healthy subjects walking at six different cadences, ranging from 70 to 120 steps/min. With increasing cadence, mean pressure–time integrals continuously decreased, mean foot-to-floor contact durations continuously decreased, and mean peak pressures increased.

Although these results suggest that variation in walking speed does significantly influence plantar pressure measurement, none of these studies recorded pressure data using the two-step gait initiation protocol. This protocol, which involves subjects striking the force platform after completing two steps, is commonly used in gait research as it offers equivalent reliability to the midgait protocol but requires less walking trials [18], [19]. However, because subjects only take two steps prior to striking the platform, it is likely that they do not achieve the same walking velocity as they would if the recordings are taken midgait. Indeed, it has been shown that steady-state gait is not achieved until the end of the second or third step [20], [21], [22], [23], [24], [25]. As such, it is possible that variations in walking speed may not be as significant a factor when recording plantar pressures using the two-step protocol. Therefore, the aim of this study was to evaluate the effects of walking speed on plantar pressure measurements obtained using the two-step gait initiation protocol. It was hypothesised that due to the small number of steps taken prior to striking the force plate using this method, differences in walking speed would have only a small impact on pressure recordings.