Research Review By Dr. Kent Stuber©

Date Posted:

June 2009

Study Title:

Effect of foot posture, foot orthoses and footwear on lower limb muscle activity during walking and running: A systematic review.

Authors:

Murley GS et al.

Author's Affiliations:

La Trobe University – Faculty of Health Sciences - Departments of Podiatry and Musculoskeletal Research Centre, Australia

Publication Information:

Gait & Posture 2009; 29: 172-187.

Background Information:

Previous research has not conclusively shown that having either a flat or high-arched foot posture puts people at higher risk of injury due to the perceived increases in tissue stress that may be involved. Still, foot posture is largely believed to influence injury risk, particularly in sports, although the mechanism linking foot posture and injury is unclear.

Developing an understanding of this relationship is important for practitioners who either prescribe or refer patients for orthotics or other interventions to treat or prevent lower limb injuries, and laboratory based research can help provide this explanation. The importance of skeletal muscle function and activation in overuse injuries is of obvious importance and electromyography (EMG) can be used to evaluate these concepts.

The authors of this systematic review set out to determine if evidence exists that demonstrates that foot posture (i.e. low or high arches), orthotics and other appliances, and footwear have an effect on lower limb muscle activation during activities, particularly walking and running.

Pertinent Results:

504 articles were originally identified in the literature search, and after applying exclusion criteria, the full text of 75 were evaluated, reducing the number of included studies to 46. After evaluating for EMG methodological reporting, only 38 had high enough EMG reporting quality to allow them be reviewed in detail for overall article quality.

The main limitations in terms of methodology of the included studies were samples not being generalizable and a lack of assessor blinding. 6 of those 38 articles looked at the effect of foot posture, 12 evaluated orthotics and other appliances, and 20 looked at the effect of footwear on lower limb muscle activity while running or walking. 37 studies used EMG, 1 used functional MRI.

Foot Posture:
In the 6 articles evaluating foot posture sample sizes ranged from 18-43 and subjects were generally young adults. Foot posture was classified in various ways such as an arch index, arch ratio, radiographic analysis, by use of 2-D video analysis, and subjective observation. 2 of the included studies looked at subjects while they were running. Vastus lateralis has been noted to initiate earlier in high-arched runners when compared with low arched runners, although this finding has been noted in one study but not another. Flat arches seem to have an important effect during walking as all 4 studies comparing this group reported significant findings for flat arches.

Tibialis anterior appears to activate more quickly in pronators. Further, pronators may have more lower limb muscle activity overall including higher activity in tibialis anterior, extensor digitorum brevis, soleus and lateral head of the gastrocnemius in varying phases of the gait cycle (as well as possibly tibialis posterior, flexor hallucis longus and flexor digitorum brevis). However in other phases of the gait cycle, activation of extensor digitorum longus, peroneus longus and brevis, soleus, and the gastrocnemius may be lower in pronators. Thus the relationship between foot posture and muscle activity remains an enigma.

Among the issues in conducting this type of research is the lack of standard classification methods for foot posture.

Orthotics and Other Appliances:
In the 12 articles evaluating orthotics sample sizes ranged from 9-40 and subjects were all young adults. Types of orthotics evaluated varied considerably including custom (4 studies) and prefabricated varieties, textured insoles, heel cups, heel lifts, wedges, ankle supports (in 2 studies). Only three of the studies evaluated subjects while running and one of those looked at both running and walking.

Custom orthotics have been evaluated in running and walking conditions using various types of custom orthotics including semi-rigid polypropylene shells, various amounts of medial wedging, dense foam (ethyl vinyl acetate) with and without wedging.

These studies have reported increases in peroneus longus and tibialis anterior activity and duration of tibialis anterior activation when wearing orthotics. Biceps femoris activity has been noted to decrease with orthotics in one study, but increase in another study. External ankle supports have been shown to decrease gastrocnemius, soleus, and peroneus activity when compared with walking. Textured insoles have shown an ability to reduce soleus and tibialis anterior activity during stance phase, whereas have soft heel cups have been shown to increase biceps femoris, tibialis anterior, and gastrocnemius activity. Heel wedges have shown an ability to change activity in the erector spinae and gluteus medius with significance albeit to a relatively small extent when considering the length of the gait cycle. Unfortunately it is still unclear whether orthotics can produce predictable changes in those who wear them, or if the decreased or increased activations recorded via EMG are clinically beneficial.

Footwear:
In the 20 articles evaluating footwear sample sizes ranges from 3-40 and subjects were generally young adults once again. Types of footwear varied from work shoes or work boots to athletic shoes to shoes with different heel heights, and unstable shoes designs.

12 studies were done with walking, seven with running, and one with both conditions employed. Of note were results in high heel wearers, unstable or destabilization shoes, and athletic footwear. Changes in lower back or lower limb muscle activity have been noted with increasing heel height and peroneus longus and the gastrocs fatigue more easily in those who regularly wear high-heels.

Conflicting results have been obtained when looking at unstable or destabilizing shoe designs. Again, unfortunately, no definitive conclusions can be reached as to the effects of athletic footwear on muscle activity during running.

Clinical Application & Conclusions:

Combinations of foot posture, footwear, and orthotics (and other appliances) have the potential to alter muscle activity (as measured by EMG). The authors could only make a few definitive conclusions:
  1. Pronators tend to have greater activation of invertor muscles and lower activation of evertor muscles.
  2. Orthotics activate tibialis anterior and peroneus longus and may affect low back muscle activation.
  3. Higher heeled shoes affect low back and lower limb muscle activation.
These basic science conclusions do not allow for much extrapolation to clinical scenarios unfortunately, as these studies were performed mostly on healthy subjects and not those seen on a daily basis by musculoskeletal injury specialists.

Still, they hopefully provide some clues to practitioners as to muscles of interest that could be further evaluated in patients presenting with, or trying to prevent lower limb overuse injuries and some possible talking points for interventions.

Study Methods:

The authors conducted a search of four different databases (Medline, CINAHL, Embase, and SPORTDiscuss) in all languages, generally with a 25 year search period (1982-2007). Articles were included if EMG or muscle function during walking or running were the main outcome measure and an independent variable of foot posture, orthotics, or footwear was involved. Neurological disease-related papers were excluded, as were single case reports, and studies assessing postural perturbation effects on muscle activity.

46 articles were assessed for study quality particularly for reporting of EMG methodology (assessed by 2 reviewers) and 38 did so adequately. These articles were then further assessed for quality by using a modified Quality Index. No attempts were made at meta-analysis.

Study Strengths/Weaknesses:

The authors conducted a comprehensive search and adding the step of ensuring valid EMG techniques was beneficial in ensuring valid results in this systematic review. Unfortunately, like many systematic reviews, this one is limited by the literature it set out to evaluate. The majority of the studies evaluated in this review were only low-to-moderate quality and generally had small sample sizes along with inadequate reporting of effect sizes and confidence intervals. This may have led to type II error.

In addition, due to the parameters and definitions used in many of the studies, comparisons were often difficult (such as comparing different studies using orthotics or when trying to compare between orthotics and foot posture). Differences in study samples and analysis prevented pooling or meta-analysis of the literature.

The authors repeatedly intimate the need for standardization in the EMG field, particularly with respect to reporting and using the most valid and reliable methods possible in gait research done with EMG. Because their criteria for reporting were fairly strict, some useful articles that did not report their EMG techniques explicitly may have been excluded. Taking all of these weaknesses together lead to conclusions that are not as firm or specific as the authors surely would have liked.

While this review does show that foot posture, footwear, and orthotics can affect lower limb muscle activity, the literature prevents us from conclusively knowing all of the muscles affected in a predictable manner and that limits the clinical utility of the findings.

Additional References:

  1. Hume P, Hopkins W, Rome K, Maulder P, Coyle G, Nigg B. Effectiveness of foot orthoses for treatment and prevention of lower limb injuries: a review. Sports Med 2008; 38(9): 759-779.