The effect of textured surfaces on postural stability and lower limb muscle activity

Abstract

Textured insoles may enhance sensory input on the plantar surfaces of the feet, thereby influencing neuromuscular function. The aim of this study was to investigate whether textured surfaces alter postural stability and lower limb muscle activity during quiet bipedal standing balance with eyes open. Anterior–posterior (AP) and mediolateral (ML) sway variables and the intensity of electromyographic (EMG) activity in eight dominant lower limb muscles were collected synchronously over 30 s in 24 young adults under three randomised conditions: control surface (C), texture 1 (T1) and texture 2 (T2). Repeated measures ANOVA showed that the textured surfaces did not significantly affect AP or ML postural sway in comparison to the control condition (p > 0.05). Neither did the textured surfaces significantly alter EMG activity in the lower limbs (p > 0.05). Under the specific conditions of this study, texture did not affect either postural sway or lower limb muscle activity in static bipedal standing. The results of this study point to three areas of further work including the effect of textured surfaces on postural stability and lower limb muscle activity: (i) in young healthy adults under more vigorous dynamic balance tests, (ii) post-fatigue, and (iii) in older adults presenting age-related deterioration.

Introduction

Recent research indicates that footwear interventions, including foot orthoses and insoles, can influence both static and dynamic functional ability (Nawoczenski and Ludewig, 1999, Bird et al., 2003, Vanicek et al., 2004, Hertel et al., 2005, Kulig et al., 2005, Nurse et al., 2005, Murley and Bird, 2006, Romkes et al., 2006).

For example, vibrating insoles have been shown to affect short-term postural sway variables in young and older adults (Priplata et al., 2003) and semi-rigid, rigid and soft foot orthoses have been shown to alter lower limb electromyographic (EMG) activity in terms of intensity (Tomaro and Burdett, 1993, Nawoczenski and Ludewig, 1999, Hertel et al., 2005, Kulig et al., 2005, Mündermann et al., 2006, Murley and Bird, 2006), onset of activity (Bird et al., 2003) and fatigue (Vanicek et al., 2004), during dynamic functional activities.

As well as changes in biomechanical alignment, motion control and facilitation of shock absorbance, enhanced sensory input to the plantar aspect of the feet has been discussed as a factor in footwear interventions (Hatton et al., 2008). It has been proposed that the presence or texture of footwear interventions may enhance sensory input influencing lower limb muscle activity during dynamic function (Hertel et al., 2005, Nurse et al., 2005) with the proposed mechanisms being alterations in the rate of discharge from mechanoreceptors, or spatio-temporal firing patterns of populations of sensory afferents in the plantar surface of the feet (Watanabe and Okubo, 1981, Waddington and Adams, 2003, Nurse et al., 2005, Wilson et al., 2008). Nurse et al., 2005 investigated the effect of textured insoles comprising semi-circular mounds with centre-to-centre distances of 8 mm, on gait patterns and reported significant reductions in tibialis anterior and soleus EMG activity. Waddington and Adams, 2000, Waddington and Adams, 2003 investigated the effect of textured versus smooth insoles on movement discrimination of ankle inversion. When substituted for smooth insoles, textured insoles restored movement discrimination back to barefoot levels. Watanabe and Okubo (1981) found that postural sway was significantly reduced when standing on a textured surface in comparison to a smooth surface. However, more recently, textured insoles with dimpled and grid surfaces have shown to have no significant effect on postural sway variables in healthy older women over a four-week period (Wilson et al., 2008). The research base on the effect of textured insoles is, therefore, limited. Also, to our knowledge, no studies have evaluated the effect of texture on static postural stability and lower limb muscle activity simultaneously.

The aims of this study were to determine whether textured surfaces alter postural stability and EMG activity during quiet standing balance in young, asymptomatic adults.

It was hypothesised that among the conditions of control (flat surface) and two textured surfaces there would be:

• differences in the magnitude of postural sway variables, and

• differences in the amplitude of lower limb EMG activity in eight lower limb muscles.