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Tuesday, June 6, 2023

Greater Activation of Abductor Hallucis in Standing versus Sitting

Brent Brookbush

Brent Brookbush


Research Review: Greater activation of abductor hallucis in standing vs sitting

By Stefanie DiCarrado DPT, PT, NASM CPT, CES, PES

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Goo, Y., Heo, H., An, D. (2014) EMG activity of the abductor hallucis muscle during foot arch exercises using different weight bearing postures. Journal of Physical Therapy Science. 10: 1635-1636 - ARTICLE

Cadeveric dissection of the plantar aspect of the foot, including labeling of commonly under-active muscles, abductor hallucis, abductor digiti and flexor digitorum brevis - By Anatomist90 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17421240
Caption: Cadeveric dissection of the plantar aspect of the foot, including labeling of commonly under-active muscles, abductor hallucis, abductor digiti and flexor digitorum brevis - By Anatomist90 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17421240

Commonly Under-active Muscles of the Plantar Surface of the Foot - By Anatomist90 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17421240

Why is this relevant?: Exercise is commonly prescribed for foot dysfunction. For example, foot doming/arch raises are commonly prescribed for individuals with fallen arches, and toe spreading is commonly prescribed to address hallucis valgus. What is not well known, is whether maximum benefit would be achieved by performing these exercises in weight bearing or non-weight bearing positions. This study provides evidence to suggest that weight-bearing has an affect on activation of the abductor hallucis.

Study Summary

Study Design Experimental Descriptive Study
Level of Evidence Level VI: Evidence from a single descriptive study
Subject Demographics
  • Age: 26.09 + 2.91
  • Gender: 6 females, 5 male
  • Characteristics:
    • Height: 166.54 + 11.54cm
    • Mass 58.45 + 14.13 kg

  • Inclusion Criteria: no symptoms of injury, able to perform exercise without pain
  • Exclusion Criteria: foot surgery within past 5 months
Outcome Measures
  • EMG % of maximal voluntary isometric contraction (MVIC) of abductor hallucis muscle
    • Toe-spreading: Standing and Sitting
    • Short-foot Exercise (a.k.a. foot dome/arch raise): Standing and Sitting

  • EMG % MVIC of abductor hallucis muscle
    • Toe-spreading: statistically significant increase in activation during standing
      • Standing: 59.19 + 14.19%
      • Sitting 47.88 + 17.95%

    • Short-foot exercise: difference in activation was not statistically significant
      • Standing: 56.43 + 14.97%
      • Sitting: 48.98 + 14.95%

ConclusionsWeight bearing positions may improve activation of foot/ankle musculature, specifically the abductor hallucis muscle during exercises such as toe spreading.  Further research should be done, with a larger sample size, to determine if the trend seen toward increased activation of the abductor hallucis in the weight bearing position of the short foot exercise is statistically significant.
Conclusions of the Researchers Standing may improve activation of the abductor hallucis muscle during toe spreading exercise.

Toe Splaying
Caption: Toe Splaying

Toe Splaying

Review & Commentary: A strength of this study is its simple design; the authors focused on a single variable (EMG of abductor hallucis) and how two positions affected that variable during two commonly used exercises. The opening literature review provided sufficient background information on the issue presented, including the effects of varied weight bearing positions on ankle/foot musculature. Subjects were selected from a homogeneous population, without ankle pain, recent injury, or a positive navicular drop test. The authors provided research validating the navicular drop test and clearly described all equipment used. Subjects practiced exercises in sitting and standing to ensure proper form prior to testing. The authors provided clear descriptions of the exercises allowing for use in a clinical setting or future research.

The authors listed the following limitations of the study; use of surface EMG, small sample size, and possibility of variations in the percentage of weight bared on the examined foot. Surface EMG does create a risk of cross talk from nearby muscles; however, the abductor hallucis is a superficial muscle and with proper electrode placement, there should be minimal, if any, interference. Unfortunately, the authors did not describe specific EMG electrode position, which may make it difficult to repeat the study and validate the data collection process. Although the sample size was small, statistically significant results during the toe-spreading exercise provide strong evidence of a relationship between weight bearing and abductor hallucis activity. Unfortunately the "short foot" exercise did not result in a difference that was statistically significant. It would be interesting to perform the study again with a larger group to determine if the trend toward increased activation on this exercise was merely by chance, or a legitimate difference. As noted by the authors, they did not measure the amount of actual weight bearing on the exercising limb, so it is unknown at this time if full versus partial weight bearing has an effect on abductor hallucis muscle activity. Further the authors did not sufficiently explain the foot position used for weight-bearing, which leg was supposed to bare the most weight, and whether dominant or non-dominant legs were examined. It would have been helpful to see pictures of the standing position as the authors described the subjects standing with their feet "splayed outwards" (what does that mean?). If the individuals were standing with excessive tibial or hip external rotation, this may affect ankle mechanics and the resting lengths of muscles crossing the ankle and foot, which may have additional unintended affects abductor hallucis activity. Despite these limitations, the evidence presented here is worth future investigation with larger sample size, fine wire EMG, better descriptions of weight bearing protocols, perhaps additional exercise selections, and or comparison to a "foot pain group".

Why is this study important?

This study provides data related to the affect of weight bearing on abductor hallucis activity, a muscle that is commonly the focus of strengthening exercise during a rehabilitation/corrective intervention for the foot. At this time, we may assume the weight bearing during the short-foot exercise may not provide any additional benefit for the abductor hallucis, but that toe spreading in weight bearing does increase abductor hallucis activity.

How does it affect practice?

As weight bearing may increase abductor hallucis activity during the toe spreading exercise it may be assumed that this is either a better choice for exercise selection, or perhaps that weight bearing is a progression of non-weight bearing exercise.

How does it relate to Brookbush Institute Content?

The Brookbush Institute is currently working on a predictive model of foot dysfunction, which will draw from the predictive model of Lower Leg Dysfunction (LLD) article. As noted within the LLD article: "most changes in relative muscle length and activity in LLD may be explained with frontal plane mechanics alone, implying that this dysfunction may stem from the inability to stabilize in the frontal plane and a propensity to evert (pronate), with sagittal and transverse plane movements of the ankle being ancillary." A lack of frontal plane stability, resulting in a collapse of the medial longitudinal arch, may be related to foot/ankle, knee, hip, and/or sacroiliac joint (SIJ) dysfunction. Please note, that although focus is placed on the foot/ankle complex in LLD , the hip, knee and SIJ should be assessed for additional contributing factors to the dysfunctional movement pattern. Signs of LLD on the overhead squat assessment include: feet turn out , feet flatten , knees bow in , knees bow out , or an excessive forward lean that will correct when the individual is asked to perform the squat again on a heel rise. This indicates to the observing clinician that the dysfunction originates from foot/ankle complex, and includes a lack of dorsiflexion. Possible causes of decreased dorsiflexion can include: anterior and medial translations of the talus at the tibiotalar joints, anterior translation of the proximal tibiofibular joint, posterior translation the proximal tibiofibular joint, as well as overactive ankle plantarflexors and evertors (lateral gastronemius , soleus , fibularis longus and brevis , and extensor digitorum longus ). Arthrokinematic assessment and correction is best performed by a license professional; however, self-administered release, and stretching techniques of the plantarflexor and evertor muscles will help, not only restore proper muscle length tension relationships, but also decrease joint stiffness allowing for improved arthokinematics. Self or manual joint mobilization, as applicable, following release techniques will further clear up arthokinematic dysfunction and create an ideal setting for activation techniques of the ankle-dorsiflexors and invertors (tibialis anterior , tibialis posterior , medial gastronemius , flexor hallucis longus and flexor digitorum longus ). Using athletic tape is a another method aimed at either increasing or decreasing muscular tone and can be applied post activation exercise to enhance carry-over from session to session.

Further consideration of the muscles and joints listed above relative to tarsal joint function should start to inspire thoughts of how intimately the ankle and joints of the foot work during functional activity. A lack of dorsiflexion will place greater load and demand for more dorsiflexion on the tarsal joints, and alterations in the activity of the tibialis anterior , tibialis posterior , extensor hallucis longus and extensor digitorum longus , flexor hallucis longus and flexor digitorum longus , have the potential to alter the length and activity of various muscles of the foot. At this point, the Brookbush Institute hypothesizes that excessive eversion, will also lead to excessive pronation of the forefoot, synergistic dominance of the long toe flexors and extensors, inhibition of the short toe flexors, as well as inhibition of the abductor hallucis, which was the subject of this research review.

The videos below demonstrate some LLD release techniques, stretching, taping of the abductor hallucis, and activation of tibialis anterior and tibialis posterior .

Gastrocnemius and Soleus Self-administered Dynamic Release a.k.a. Pin and Stretch

Slant Board Calf and Fibularis Muscle Stretch:

Quick Tibialis Anterior and Tibial Internal Rotator Activation

Posterior Tibialis Activation Progression 4

Kinesiology Taping - Toe Abduction Taping (1st & 5th Metatarsophalangeal Abduction)

© 2016 Brent Brookbush

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