Standing in an unstable shoe increases postural sway and muscle activity of selected smaller extrinsic foot muscles

doi:10.1016/j.gaitpost.2010.04.018

Gait & Posture

Volume 32, Issue 2, June 2010, Pages 215-219

https://doi.org/10.1016/j.gaitpost.2010.04.018 Get rights and content

Abstract

Inactivity or the under-utilization of lower limb muscles can lead to strength and functional deficits and potential injury. Traditional shoes with stability and support features can overprotect the foot and potentially contribute to the deterioration of the smaller extrinsic foot muscles. Healthy subjects (n = 28) stood in an unstable MBT (Masai Barefoot Technology) shoe during their work day for a 6-week accommodation period. A two-way repeated measures ANOVA was used to determine (i) if unstable shoe wear increased electromyographic (EMG) activity of selected extrinsic foot muscles and increased postural sway compared to standing barefoot and in a stable control shoe and (ii) if postural sway and muscle activity across footwear conditions differed between a pre- and post-accommodation testing visit. Using an EMG circumferential linear array, it was shown that standing in the unstable shoe increased activity of the flexor digitorum longus, peroneal (PR) and anterior compartment (AC) muscles of the lower leg. No activity differences for the larger soleus (SOL) were identified between the stable and unstable shoe conditions. Postural sway was greater while standing in the unstable shoe compared to barefoot and the stable control shoe. These findings suggest that standing in the unstable MBT shoe effectively activates selected extrinsic foot muscles and could have implications for strengthening and conditioning these muscles. Postural sway while standing in the unstable MBT shoe also decreased over the 6-week accommodation period.

Introduction

Shoes are traditionally designed to improve stability and support the foot during locomotion, often with the goal of controlling such movements as pronation. It has been suggested in coaching circles and in the biomechanical community that (i) these shoe design features may lead to an overprotection and/or under-utilization of the smaller extrinsic foot muscles and (ii) training barefoot can be an effective method for strengthening foot and ankle muscles [1]. The under-utilization of muscles over time can result in reduced strength or weakness [2] and combined with muscle imbalances, can lead to increased injury susceptibility of the lower limb and back [3], [4], [5], [6], [7]. Unstable training devices such as wobble boards have proven effective in reducing injury in younger and older populations and this training enhances proprioception, improves muscle coordination and may even strengthen select muscles [8], [9], [10]. Recently, unstable shoes have been developed to simulate an effect similar to the wobble board, with the primary purpose of activating and strengthening muscles that may be relatively inactive and under-utilized while wearing a more stable shoe.

Masai Barefoot Technology (MBT) is an unstable shoe with a rounded sole that provides instability in the anterior–posterior direction and a cushioned heel sensor that provides instability in the medial–lateral direction. This design attempts to simulate an unstable surface, thereby requiring continual activation of important stabilizing muscles of the lower limb to maintain proper balance. Evidence exists that wearing the unstable MBT can contribute to a significant reduction in knee and low back pain [11], [12].

The biomechanical and neuromuscular changes introduced by wearing unstable shoes have also been investigated [13], [14], [15]. Walking and standing in an unstable MBT shoe provides training to some of the larger extrinsic foot muscles crossing the ankle joint complex, specifically increasing activity of the gastrocnemius and tibialis anterior [14], [15]. No study, however, has quantified muscle activity for some of the smaller extrinsic foot muscles important for stabilizing and controlling the foot, such as the peroneus longus and flexor digitorum longus.

Most small extrinsic foot muscles (e.g. peroneus longus and brevis, flexor hallucis longus and tibialis posterior) have short moment arms about the talocrural joint (plantar- and dorsi-flexion) but more effective moment arms about the subtalar joint (inversion–eversion) [16]. A continuous engagement of these smaller muscles could lead to more effective control of movements and moments about the subtalar joint and potentially contribute to a reduction in joint loading and joint pain [1], [17].

Quantification of activity of some smaller extrinsic foot muscles can be done invasively with indwelling electrodes [18] or non-invasively with a custom designed EMG circumferential linear array of several bipolar EMG electrode pairs adjacent to each. This array is capable of measuring individual activity of selected small extrinsic foot muscles and is suitable for studying the interplay between multiple muscles during tasks such as walking and standing [19].

The purpose of this study was to (i) quantify muscle activity of select small extrinsic foot muscles using a circumferential linear EMG array proximal to the ankle joint and (ii) quantify postural sway while standing barefoot, in an unstable MBT shoe and in a stable control shoe. Measurements were also compared before and after a 6-week accommodation period of wearing the unstable MBT shoe to determine if improvements in postural control occurred as a possible result of increased muscle training and strengthening.

The following hypotheses were tested:

For selected smaller muscles including the peroneus brevis/longus and flexor digitorum longus, the initial muscle activity while standing in an unstable MBT shoe will be greater than standing barefoot or in a stable control shoe.

After using the unstable MBT shoe for 6 weeks, the muscle activity for the same smaller muscles while standing in an unstable MBT shoe will remain greater than standing barefoot or in a stable control shoe.

Initial postural sway while standing in an unstable MBT shoe will be greater than standing barefoot or in a stable control shoe.

After using the unstable MBT shoe for 6 weeks, postural sway while standing in an unstable MBT shoe will be greater than standing barefoot or in a stable control shoe.

Section snippets

Subjects

Twenty-eight subjects (19 females, 9 males) participated in this study and meet the criteria in Table 1. The study was approved by the University of Calgary's Office of Medical Bioethics and all subjects signed a written consent form prior to testing. A priori power analysis (β = 0.2, p = 0.05) using previous Center of Pressure (CoP) excursion and EMG data [14] demonstrated adequate power would be achieved with 28 subjects.

Testing protocol overview

The study was completed in the Human Performance Laboratory (HPL) and

EMG-activity intensities

Comparing activity wavelet intensities, neither visit (pre- and post-accommodation testing) nor interaction effects were identified for all muscle groups (Table 2 and Fig. 2). A shoe effect was evident for the four muscle groups and based on the small p-values, Bonferroni pairwise comparisons were performed (Table 3). For both testing visits, the unstable MBT shoe produced larger intensities compared to the other two footwear conditions for the FDL and AC muscle group. No differences were

Discussion

Several shoe companies have recently developed so called “barefoot” shoes [1] with the purpose of providing some of the suggested benefits of barefoot locomotion. Being conceptually similar to wobble board training during injury rehabilitation, the unstable MBT shoe is one of these “barefoot” shoes designed to train or activate some of the smaller extrinsic foot muscles while standing or walking. Evidence for the effectiveness of wobble board training does exists [9], [10], [21], however, such

Conflict of interest statement

While Masai Barefoot Technology (MBT) provided the unstable shoes and financial support, they had no role in (i) the study design, (ii) the collection, analysis and interpretation of the data, (iii) the writing of the manuscript or (iv) the decision to submit the manuscript for publication.

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Methodical heterogeneity of bipedal static posturography hampers studies’ comparability. Thus, we provide a standardized approach to increase knowledge whether habitual footwear decrease postural control in comparison to barefoot stance.
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Soleus is an effective plantar flexor that has distinct functional roles and behaves differently during different biomechanical actions. Different footwear types may give rise to adjusted muscular effort and biomechanics of Soleus muscle action. Consequent altered ground reaction forces created at the foot may give rise to injuries/fatigue during different activities. Relatively little is known about in vivo behavior of the Soleus muscle during walking and running. Surface Electromyography (SEMG) is commonly analyzed by researchers to understand lower limb muscle activity. The Objective of this study was to systematically review available research literature investigating Soleus SEMG activity in healthy subjects under different footwear conditions during different tasks.
Methods: electronic databases PUBMED, EBSCOHOST (Academic Elite) and SCIENCEDIRECT were searched on 30.11.2020 for the combination of keywords “Surface Electromyography” AND “Shoe” AND “Soleus”. Inclusion and exclusion criteria were specified in advance. The methodological quality of each relevant study was independently evaluated for “Risk of bias” on Modified Downs and Black checklist. Studies with quality score >50% were considered reasonable to be included in this review.
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Standing in an unstable shoe increases postural sway and muscle activity of selected smaller extrinsic foot muscles

Abstract

Introduction

Section snippets

Subjects

Testing protocol overview

EMG-activity intensities

Discussion

Conflict of interest statement

Gait Posture

Clin Biomech (Bristol, Avon)

Clin Biomech (Bristol, Avon)

J Electromyogr Kinesiol

J Biomech

Biomechanical considerations on barefoot movement and barefoot shoe concepts

Footwear Sci

The molecular basis of skeletal muscle atrophy

Am J Physiol Cell Physiol

Preseason hamstring muscle weakness associated with hamstring muscle injury in Australian footballers

Am J Sports Med

A prospective study of ankle injury risk factors