Clinical Research and the FootCore MAX

The FootCore MAX is built on the scientific contributions of hundreds of scientists and 130+ clinical studies.

The research is clear: the best pathway to living pain free is to strengthen your feet. The FootCore MAX is precisely engineered to help you do that quickly, painlessly, and affordably.

See the clinical research done on intrinsic muscle strength and the following topics. You will find highlighted abstracts from clinical studies and treatment protocols.

Flat FeetInjury RecoveryPlantar FasciitisAnkle & TendonitisBalance & AthleticismKnee FunctionDiabetes and Other ConditionsRunners & Injury PreventionIntrinsic Muscle Theory

"Clearly, a stronger foot is a healthier foot. To this end, we are suggesting a paradigm shift in the way we think about treating the foot. Current clinical guidelines include the use of foot orthotic devices for heel pain and plantar fasciitis, but lack any reference to strengthening of the foot...Our feet were designed with the strength for unsupported endurance walking and running. Unfortunately, adding permanent support to the foot, as opposed to strengthening the foot core, is the current standard of care."

McKeon PO, Hertel J, Bramble D, et al The foot core system: a new paradigm for understanding intrinsic foot muscle function British Journal of Sports Medicine 2015;49:290.

Intrinsic Muscles and Flat Feet

Flat feet or pes planus can be corrected with foot strengthening.

For individuals with pes planus [flat feet], the short-foot exercise effectively corrected static foot alignment and temporal parameters of foot kinematics during gait. This temporal change, which shortens the time for navicular height to reach its minimum value, indicates an improved windlass mechanism. Therefore, short-foot exercise might effectively prevent or treat injuries related to the pes planus alignment.

"Effects of plantar intrinsic foot muscle strengthening exercise on static and dynamic foot kinematics: A pilot randomized controlled single-blind trial in individuals with pes planus.Okamura K, Fukuda K, Oki S, Ono T, Tanaka S, Kanai S.
Gait Posture. 2020 Jan;75:40-45. doi: 10.1016/j.gaitpost.2019.09.030. Epub 2019 Sep 29.
PMID: 31590069 Clinical Trial."

Subject ND decreased by a mean of 1.8 mm at 4 weeks and 2.2 mm at 8 weeks (p < 0.05). AHI increased from 28 to 29% (p < 0.05). Intrinsic foot muscle performance during a static unilateral balancing activity improved from a grade of fair to good (p < 0.001) and subjects experienced a significant improvement during a functional balance and reach task in all directions with the exception of an anterior reach (p < 0.05). This study offers preliminary evidence to suggest that SFE training may have value in statically and dynamically supporting the MLA.

"Effect of plantar intrinsic muscle training on medial longitudinal arch morphology and dynamic function.Mulligan EP, Cook PG. Man Ther. 2013 Oct;18(5):425-30. doi: 10.1016/j.math.2013.02.007. Epub 2013 Apr 28.
PMID: 23632367"

We found that recruitment of the intrinsic foot muscles increased with increasing load, beyond specific load thresholds. Interestingly, LA deformation and muscle stretch plateaued towards the maximum load of 150% body weight, when muscle activity was greatest. Electrical stimulation of the plantar intrinsic muscles countered the deformation that occurred owing to the application of external load by reducing the length and increasing the height of the LA. These findings demonstrate that these muscles have the capacity to control foot posture and LA stiffness and may provide a buttressing effect during foot loading.

"Intrinsic foot muscles have the capacity to control deformation of the longitudinal arch.Kelly LA, Cresswell AG, Racinais S, Whiteley R, Lichtwark G. J R Soc Interface. 2014 Jan 29;11(93):20131188. doi: 10.1098/rsif.2013.1188. Print 2014 Apr 6.
PMID: 24478287 Free PMC article. Clinical Trial."

The results revealed that in flat-footed subjects, the PIFMs have the capacity to support the MLA enough to change foot kinematics during gait. Strengthening these muscles may be effective in preventing or treating lower extremity overuse injuries related to flat-foot alignment.

"The effect of additional activation of the plantar intrinsic foot muscles on foot kinematics in flat-footed subjects. Okamura K, Kanai S, Fukuda K, Tanaka S, Ono T, Oki S.
Foot (Edinb). 2019 Mar;38:19-23. doi: 10.1016/j.foot.2018.11.002. Epub 2018 Nov 6.
PMID: 30530189 Clinical Trial."

Results: Navicular drop, Foot Posture Index, pain, and disability scores were significantly decreased; maximum plantar force of midfoot was significantly increased in short-foot exercises group over 6 weeks (P < .05). No significant differences were determined between the baseline and the sixth week outcomes in control group (P > .05). Conclusions: Six-week short-foot exercises provided a reduction in navicular drop, foot pronation, foot pain, and disability and increment in plantar force of medial midfoot in pes planus.

"Effects of Short-Foot Exercises on Foot Posture, Pain, Disability, and Plantar Pressure in Pes Planus.Unver B, Erdem EU, Akbas E.
J Sport Rehabil. 2019 Jun 16:1-5. doi: 10.1123/jsr.2018-0363. Online ahead of print.
PMID: 30860412"

  • "Effect of foot orthoses and short-foot exercise on the cross-sectional area of the abductor hallucis muscle in subjects with pes planus: a randomized controlled trial.Jung DY, Koh EK, Kwon OY.
    J Back Musculoskelet Rehabil. 2011;24(4):225-31. doi: 10.3233/BMR-2011-0299.
    PMID: 22142711 Clinical Trial."
  • "Effects of the Short Foot Exercise With Neuromuscular Electrical Stimulation on Navicular Height in Flexible Flatfoot in Thailand: A Randomized Controlled Trial.Namsawang J, Eungpinichpong W, Vichiansiri R, Rattanathongkom S.
    J Prev Med Public Health. 2019 Jul;52(4):250-257. doi: 10.3961/jpmph.19.072. Epub 2019 Jul 14.
    PMID: 31390688 Free PMC article. Clinical Trial."
  • "The effects of short foot exercises and arch support insoles on improvement in the medial longitudinal arch and dynamic balance of flexible flatfoot patients.Kim EK, Kim JS.
    J Phys Ther Sci. 2016 Nov;28(11):3136-3139. doi: 10.1589/jpts.28.3136. Epub 2016 Nov 29.
    PMID: 27942135 Free PMC article."
  • "Differences in the angle of the medial longitudinal arch and muscle activity of the abductor hallucis and tibialis anterior during sitting short-foot exercises between subjects with pes planus and subjects with neutral foot.Lee JH, Cynn HS, Yoon TL, Choi SA, Kang TW.
    J Back Musculoskelet Rehabil. 2016 Nov 21;29(4):809-815. doi: 10.3233/BMR-160693.
    PMID: 27002666"
  • "Immediate and short-term radiological changes after combining static stretching and transcutaneous electrical stimulation in adults with cavus foot: A randomized controlled trial.Fernández-Seguín LM, Heredia-Rizo AM, Díaz-Mancha JA, González-García P, Ramos-Ortega J, Munuera-Martínez PV.
    Medicine (Baltimore). 2019 Nov;98(46):e18018. doi: 10.1097/MD.0000000000018018.
    PMID: 31725676 Free PMC article. Clinical Trial."
  • "Does the weakening of intrinsic foot muscles cause the decrease of medial longitudinal arch height?Okamura K, Kanai S, Oki S, Tanaka S, Hirata N, Sakamura Y, Idemoto N, Wada H, Otsuka A.
    J Phys Ther Sci. 2017 Jun;29(6):1001-1005. doi: 10.1589/jpts.29.1001. Epub 2017 Jun 7.
    PMID: 28626309 Free PMC article."
  • "Fatigue of the plantar intrinsic foot muscles increases navicular drop.Headlee DL, Leonard JL, Hart JM, Ingersoll CD, Hertel J.
    J Electromyogr Kinesiol. 2008 Jun;18(3):420-5. doi: 10.1016/j.jelekin.2006.11.004. Epub 2007 Jan 8.
    PMID: 17208458"
  • "Inframalleolar Varus Deformity: Role of Calcaneal Osteotomies.Usuelli FG, Manzi L.
    Foot Ankle Clin. 2019 Jun;24(2):219-237. doi: 10.1016/j.fcl.2019.02.011. Epub 2019 Apr 5.
    PMID: 31036266 Review."
  • "Flexible flatfoot.Atik A, Ozyurek S.
    North Clin Istanb. 2014 Aug 3;1(1):57-64. doi: 10.14744/nci.2014.29292. eCollection 2014.
    PMID: 28058304 Free PMC article."
  • "The effect of a 12-week custom foot orthotic intervention on muscle size and muscle activity of the intrinsic foot muscle of young adults during gait termination.Protopapas K, Perry SD.
    Clin Biomech (Bristol, Avon). 2020 Aug;78:105063. doi: 10.1016/j.clinbiomech.2020.105063. Epub 2020 May 28.
    PMID: 32521283"
  • "Foot exercise and taping in patients with patellofemoral pain and pronated foot.Lee J, Yoon J, Cynn H.
    J Bodyw Mov Ther. 2017 Jan;21(1):216-222. doi: 10.1016/j.jbmt.2016.07.010. Epub 2016 Aug 12.
    PMID: 28167183 Clinical Trial."
  • "Differences in foot muscle morphology and foot kinematics between symptomatic and asymptomatic pronated feet.Zhang X, Pauel R, Deschamps K, Jonkers I, Vanwanseele B.
    Scand J Med Sci Sports. 2019 Nov;29(11):1766-1773. doi: 10.1111/sms.13512. Epub 2019 Jul 26.
    PMID: 31278774"
  • "Randomized Clinical Trial: The Effect of Exercise of the Intrinsic Muscle on Foot Pronation.Pabón-Carrasco M, Castro-Méndez A, Vilar-Palomo S, Jiménez-Cebrián AM, García-Paya I, Palomo-Toucedo IC.
    Int J Environ Res Public Health. 2020 Jul 7;17(13):4882. doi: 10.3390/ijerph17134882.
    PMID: 32645830 Free PMC article."

Intrinsic Muscles and Injury Recovery

Medical Professionals are encouraged to incorporate intrinsic muscle strengthening into injury recovery protocols.

The intrinsic muscles of the foot play a critical role in the regulation of absorption and propulsion during dynamic activities. Dysfunction of these may lead to an increased demand on the remaining components within the foot core system to maintain dynamic foot control, leading to a more rapid breakdown of these contributors and those proximal to the foot. 

"Freeing the foot: integrating the foot core system into rehabilitation for lower extremity injuries.McKeon PO, Fourchet F.
Clin Sports Med. 2015 Apr;34(2):347-61. doi: 10.1016/j.csm.2014.12.002. Epub 2015 Jan 24. PMID: 25818718 Review."

  • "The effectiveness of exercise on recovery and clinical outcomes of soft tissue injuries of the leg, ankle, and foot: A systematic review by the Ontario Protocol for Traffic Injury Management (OPTIMa) Collaboration.Woitzik E, Jacobs C, Wong JJ, Côté P, Shearer HM, Randhawa K, Sutton D, Southerst D, Varatharajan S, Brison RJ, Yu H, van der Velde G, Stern PJ, Taylor-Vaisey A, Stupar M, Mior S, Carroll LJ.
    Man Ther. 2015 Oct;20(5):633-45. doi: 10.1016/j.math.2015.03.012. Epub 2015 Mar 28.
    PMID: 25892707"
  • "Reverse-Flow Intrinsic Fasciocutaneous Island Flaps in Foot Reconstruction.Bahk S, Doh G, Hong KY, Lim S, Eo S.
    Int J Low Extrem Wounds. 2017 Dec;16(4):296-301. doi: 10.1177/1534734617740253. Epub 2017 Nov 13. PMID: 29132254"
  • "The mangled foot and ankle: soft tissue salvage techniques.Hallock GG. Clin Podiatr Med Surg. 2014 Oct;31(4):565-76. doi: 10.1016/j.cpm.2014.06.006. Epub 2014 Aug 5. PMID: 25281516 Review."

Intrinsic Muscles and Plantar Fasciitis

Foot strengthening is an effective treatment to alleviate the pain of plantar fasciitis. 

Overuse injury is the primary contributing factor in tendinopathy. The close anatomic proximity and mechanical function of these muscles relative to the plantar fascia suggests potential for proximal plantar intrinsic tendinopathy as a result of repetitive loading during gait and other weight-bearing activities.

"Proximal Plantar Intrinsic Tendinopathy: Anatomical and Biomechanical Considerations in Plantar Heel Pain.Christie S, Styn G Jr, Ford G, Terryberry K. J Am Podiatr Med Assoc. 2019 Sep;109(5):412-415. doi: 10.7547/17-198.
PMID: 31599667"

Improvements were found in all groups regarding the visual analog scale, the pain, activities of daily living, sports and recreation, quality of life (p < 0.001) and other symptoms (p < 0.01) subscales of the Foot and Ankle Outcome Score as well as posterolateral movement, posteromedial movement and composite score (p < 0.001) on the Star Excursion Balance Test. No time-group interactions were found for any of the variables (p > 0.05).

"Effect of stretching with and without muscle strengthening exercises for the foot and hip in patients with plantar fasciitis: A randomized controlled single-blind clinical trial.Kamonseki DH, Gonçalves GA, Yi LC, Júnior IL. Man Ther. 2016 Jun;23:76-82. doi: 10.1016/j.math.2015.10.006. Epub 2015 Oct 30.
PMID: 26654252 Clinical Trial."

  • "Foot orthoses for plantar heel pain: a systematic review and meta-analysis.Whittaker GA, Munteanu SE, Menz HB, Tan JM, Rabusin CL, Landorf KB. Br J Sports Med. 2018 Mar;52(5):322-328. doi: 10.1136/bjsports-2016-097355. Epub 2017 Sep 21.
    PMID: 28935689 Review."
  • "Manual physical therapy and exercise versus electrophysical agents and exercise in the management of plantar heel pain: a multicenter randomized clinical trial.Cleland JA, Abbott JH, Kidd MO, Stockwell S, Cheney S, Gerrard DF, Flynn TW. J Orthop Sports Phys Ther. 2009 Aug;39(8):573-85. doi: 10.2519/jospt.2009.3036.
    PMID: 19687575 Clinical Trial."
  • "Strength training for plantar fasciitis and the intrinsic foot musculature: A systematic review.Huffer D, Hing W, Newton R, Clair M.
    Phys Ther Sport. 2017 Mar;24:44-52. doi: 10.1016/j.ptsp.2016.08.008. Epub 2016 Aug 18.
    PMID: 27692740 Review."
  • "Morphological and mechanical properties of plantar fascia and intrinsic foot muscles in individuals with and without flat foot.Taş S, Ünlüer NÖ, Korkusuz F. J Orthop Surg (Hong Kong). 2018 May-Aug;26(3):2309499018802482. doi: 10.1177/2309499018802482.
    PMID: 30270752"
  • "The evalaution of the foot core system in individuals with plantar heel pain.Hogan KK, Prince JA, Hoch MC. Phys Ther Sport. 2020 Mar;42:75-81. doi: 10.1016/j.ptsp.2019.11.011. Epub 2019 Nov 29.
    PMID: 31951848"
  • "An investigation of the relationship between plantar pressure distribution and the morphologic and mechanic properties of the intrinsic foot muscles and plantar fascia.Taş S, Çetin A. Gait Posture. 2019 Jul;72:217-221. doi: 10.1016/j.gaitpost.2019.06.021. Epub 2019 Jun 26.
    PMID: 31260859"
  • "Recruitment of the plantar intrinsic foot muscles with increasing postural demand.Kelly LA, Kuitunen S, Racinais S, Cresswell AG.
    Clin Biomech (Bristol, Avon). 2012 Jan;27(1):46-51. doi: 10.1016/j.clinbiomech.2011.07.013. Epub 2011 Aug 23.
    PMID: 21864955"
  • "The effect of additional activation of the plantar intrinsic foot muscles on foot dynamics during gait.Okamura K, Kanai S, Hasegawa M, Otsuka A, Oki S. Foot (Edinb). 2018 Mar;34:1-5. doi: 10.1016/j.foot.2017.08.002. Epub 2017 Aug 18.
    PMID: 29175714 Clinical Trial."

Intrinsic Muscles, Ankles, Posterior Tendonitis, Achilles Tendonitis 

Overuse injuries like tendonitis can be prevented and treated with foot strengthening.

The interplay of segmental joint mobility, afferent and efferent sensorimotor function, and movement and stabilization provided by the extrinsic and intrinsic musculature is required to coordinate and execute the complex kinematic movements in the ankle-foot complex during propulsion.

"MIDFOOT AND FOREFOOT INVOLVEMENT IN LATERAL ANKLE SPRAINS AND CHRONIC ANKLE INSTABILITY. PART 1: ANATOMY AND BIOMECHANICS.Fraser JJ, Feger MA, Hertel J.
Int J Sports Phys Ther. 2016 Dec;11(6):992-1005.

We measured the activation rate and dynamic balance of the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and quadratus plantae before and after the intervention. We found that the activation rate and dynamic balance significantly increased in all intrinsic foot muscles in the experimental group. These results suggest that intrinsic foot muscle exercise for patients with chronic ankle stability is an effective treatment for improving the functions and balance ability of the intrinsic foot muscles.

"Effects of a 6-week intrinsic foot muscle exercise program on the functions of intrinsic foot muscle and dynamic balance in patients with chronic ankle instability.Lee DR, Choi YE.
J Exerc Rehabil. 2019 Oct 28;15(5):709-714. doi: 10.12965/jer.1938488.244. eCollection 2019 Oct.
PMID: 31723561 Free PMC article."

 Our 4-week SFE program may have positive effects on changing muscle activation patterns for tibialis anterior and fibularis longus muscles, although it could not influence their structural deformity and ankle joint moment. It could produce a potential benefit of decreased tibialis posterior activation.

"Effects of a 4-Week Short-Foot Exercise Program on Gait Characteristics in Patients With Stage II Posterior Tibial Tendon Dysfunction.Kim J, Lee SC, Chun Y, Jun HP, Seegmiller JG, Kim KM, Lee SY.
J Sport Rehabil. 2020 Mar 31:1-9. doi: 10.1123/jsr.2019-0211. Online ahead of print.
PMID: 32235000"

  • Short-Foot Exercise Promotes Quantitative Somatosensory Function in Ankle Instability: A Randomized Controlled Trial.Lee E, Cho J, Lee S. Med Sci Monit. 2019 Jan 21;25:618-626. doi: 10.12659/MSM.912785. PMID: 30665229 Free PMC article. Clinical Trial.
  • "The Effect of an Inclined Ankle on the Activation of the Abductor Hallucis Muscle during Short Foot Exercise.Heo HJ, An DH.
    J Phys Ther Sci. 2014 Apr;26(4):619-20. doi: 10.1589/jpts.26.619. Epub 2014 Apr 23.
    PMID: 24764646 Free PMC article."
  • "Intrinsic foot muscles morphological modifications in patients with Achilles tendinopathy: A novel case-control research study.Romero-Morales C, Martín-Llantino PJ, Calvo-Lobo C, Almazán-Polo J, López-López D, de la Cruz-Torres B, Palomo-López P, Rodríguez-Sanz D.
    Phys Ther Sport. 2019 Nov;40:208-212. doi: 10.1016/j.ptsp.2019.09.014. Epub 2019 Oct 3.
    PMID: 31593918 Clinical Trial."
  • "Tendinopathies of the foot and ankle.Simpson MR, Howard TM.
    Am Fam Physician. 2009 Nov 15;80(10):1107-14.
    PMID: 19904895 Review."
  • "Direct measurement of the intrinsic ankle stiffness during standing.Vlutters M, Boonstra TA, Schouten AC, van der Kooij H.
    J Biomech. 2015 May 1;48(7):1258-63. doi: 10.1016/j.jbiomech.2015.03.004. Epub 2015 Mar 19.
    PMID: 25843262"
  • "The intrinsic foot muscles are purely innervated by the tibial nerve (""all tibial foot"")--an unusual innervation anomaly.Linden D, Berlit P.
    Muscle Nerve. 1994 May;17(5):560-1.
    PMID: 8159190 No abstract available."
  • "Tendinopathies of the foot and ankle.Simpson MR, Howard TM.
    Am Fam Physician. 2009 Nov 15;80(10):1107-14.
    PMID: 19904895 Review."
  • "Tendonitis and Tendinopathy: What Are They and How Do They Evolve?Federer AE, Steele JR, Dekker TJ, Liles JL, Adams SB.
    Foot Ankle Clin. 2017 Dec;22(4):665-676. doi: 10.1016/j.fcl.2017.07.002. Epub 2017 Sep 27.
    PMID: 29078821 Review."

Intrinsic Muscles and Balance

Strengthening your feet is a great way to improve your balance. 

The sequential peak activity of MTP flexors followed by MTP extensors suggests that their biomechanical contributions may be largely separable from each other and from other extrinsic foot muscles during walking. Meanwhile, the task-specific coordination of the foot muscles during other modes of locomotion indicates a high-level of specificity in their function and control.

"Coordination of intrinsic and extrinsic foot muscles during walking.Zelik KE, La Scaleia V, Ivanenko YP, Lacquaniti F.
Eur J Appl Physiol. 2015 Apr;115(4):691-701. doi: 10.1007/s00421-014-3056-x. Epub 2014 Nov 25.
PMID: 25420444"

These results suggest that larger AbH, FDB and FHB muscles are related to reduced performance in single-leg stance balance tests, whereas higher AbH and FHB stiffness are related to better performance in single-leg stance balance tests in healthy sedentary young females.

"Thickness, cross-sectional area, and stiffness of intrinsic foot muscles affect performance in single-leg stance balance tests in healthy sedentary young females.Taş S, Ünlüer NÖ, Çetin A.
J Biomech. 2020 Jan 23;99:109530. doi: 10.1016/j.jbiomech.2019.109530. Epub 2019 Nov 20.
PMID: 31785820"

  • "Effects of plantar intrinsic foot muscle strengthening exercise on static and dynamic foot kinematics: A pilot randomized controlled single-blind trial in individuals with pes planus.Okamura K, Fukuda K, Oki S, Ono T, Tanaka S, Kanai S.
    Gait Posture. 2020 Jan;75:40-45. doi: 10.1016/j.gaitpost.2019.09.030. Epub 2019 Sep 29.
    PMID: 31590069 Clinical Trial."
  • "Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing.Zhang X, Schütte KH, Vanwanseele B.
    Gait Posture. 2017 Sep;57:52-56. doi: 10.1016/j.gaitpost.2017.05.027. Epub 2017 May 25.
    PMID: 28575753"
  • "The functional importance of human foot muscles for bipedal locomotion.Farris DJ, Kelly LA, Cresswell AG, Lichtwark GA.
    Proc Natl Acad Sci U S A. 2019 Jan 29;116(5):1645-1650. doi: 10.1073/pnas.1812820116. Epub 2019 Jan 17.
    PMID: 30655349 Free PMC article."
  • "Intrinsic foot muscles act to stabilise the foot when greater fluctuations in centre of pressure movement result from increased postural balance challenge.Ferrari E, Cooper G, Reeves ND, Hodson-Tole EF.
    Gait Posture. 2020 Jun;79:229-233. doi: 10.1016/j.gaitpost.2020.03.011. Epub 2020 May 11.
    PMID: 32446178"
  • "Wide-pulse electrical stimulation to an intrinsic foot muscle induces acute functional changes in forefoot-rearfoot coupling behaviour during walking.James DC, Chesters T, Sumners DP, Cook DP, Green DA, Mileva KN.
    Int J Sports Med. 2013 May;34(5):438-43. doi: 10.1055/s-0032-1321893. Epub 2012 Oct 11.
    PMID: 23059559 Clinical Trial."
  • "Regulation of foot and ankle quasi-stiffness during human hopping across a range of frequencies.Kessler SE, Lichtwark GA, Welte LKM, Rainbow MJ, Kelly LA.
    J Biomech. 2020 Jul 17;108:109853. doi: 10.1016/j.jbiomech.2020.109853. Epub 2020 May 22.
    PMID: 32636016"
  • "Differences in static- and dynamic-balance task performance after 4 weeks of intrinsic-foot-muscle training: the short-foot exercise versus the towel-curl exercise.Lynn SK, Padilla RA, Tsang KK.
    J Sport Rehabil. 2012 Nov;21(4):327-33. doi: 10.1123/jsr.21.4.327. Epub 2012 Jun 18.
    PMID: 22715143 Clinical Trial."

Foot Intrinsics and Knee Function

Flat feet can throw off your knee but strong feet can correct the problem.

This study examined the influence of SFE using visual feedback on the balance and accuracy of knee joint movements in subjects with flatfoot and demonstrated that this exercise, using visual feedback, improved the balance and accuracy of knee movement.

"The effect of short foot exercise using visual feedback on the balance and accuracy of knee joint movement in subjects with flexible flatfoot.Kim JS, Lee MY.
Medicine (Baltimore). 2020 Mar;99(13):e19260. doi: 10.1097/MD.0000000000019260.
PMID: 32221061 Free PMC article. Clinical Trial."

  • "Nonsurgical Management of Knee Pain in Adults.Jones BQ, Covey CJ, Sineath MH Jr.
    Am Fam Physician. 2015 Nov 15;92(10):875-83.
    PMID: 26554281"
  • "Effect of equinus foot placement and intrinsic muscle response on knee extension during stance.Higginson JS, Zajac FE, Neptune RR, Kautz SA, Burgar CG, Delp SL.
    Gait Posture. 2006 Jan;23(1):32-6. doi: 10.1016/j.gaitpost.2004.11.011. Epub 2005 Jan 9.
    PMID: 16311192"
  • "Patellofemoral pain syndrome.Petersen W, Ellermann A, Gösele-Koppenburg A, Best R, Rembitzki IV, Brüggemann GP, Liebau C.
    Knee Surg Sports Traumatol Arthrosc. 2014 Oct;22(10):2264-74. doi: 10.1007/s00167-013-2759-6. Epub 2013 Nov 13.
    PMID: 24221245 Free PMC article. Review."

Diabetes, Other Conditions, and Foot Intrinsic Strength

Diabetics with strong feet have much healthier and sensitive feet.

The results showed that intrinsic muscle weakness was present more frequent in patients with impaired sensibility (P=0.001), also 20% of the population had intrinsic muscle weakness in the presence of normal sensibility. Multivariate regression analysis showed that only age is associated with patients with diabetes presenting normal sensibility but impaired intrinsic muscle function (P=0.017).

"Detecting intrinsic muscle weakness of the hallux as an addition to early-stage screening of the feet in patients with diabetes.Mahieu R, Coenen MN, van Bemmel T, van der Zaag-Loonen HJ, Theuvenet WJ.
Diabetes Res Clin Pract. 2016 Sep;119:83-7. doi: 10.1016/j.diabres.2016.07.007. Epub 2016 Jul 28.
PMID: 27497143"

Our experience dictates, patients with rigid deformity and limited joint mobility get caught in the cycle of repetitive stress and cannot break the cycle until the etiology of the structural deformity is addressed surgically and preventative strategies for off loading, temperature monitoring, and activity level are implemented.

"Prevention: can we stop problems before they arise? Rhim B, Harkless L.
Semin Vasc Surg. 2012 Jun;25(2):122-8. doi: 10.1053/j.semvascsurg.2012.05.002.
PMID: 22817863 Review."

Synopsis Hallux valgus is a progressive deformity of the first metatarsophalangeal joint that changes the anatomy and biomechanics of the foot. To date, surgery is the only treatment to correct this deformity, though the recurrence rate is as high as 15%. This clinical commentary provides instruction in a strengthening approach for treatment of hallux valgus deformity, by addressing the moment actions of 5 muscles identified as having the ability to counter the hallux valgus process.

"Treatment of Progressive First Metatarsophalangeal Hallux Valgus Deformity: A Biomechanically Based Muscle-Strengthening Approach.Glasoe WM.
J Orthop Sports Phys Ther. 2016 Jul;46(7):596-605. doi: 10.2519/jospt.2016.6704. Epub 2016 Jun 6.
PMID: 27266887"

  • "Can ultrasound measures of intrinsic foot muscles and plantar soft tissues predict future diabetes-related foot disease? A systematic review.Morrison T, Jones S, Causby RS, Thoirs K.
    PLoS One. 2018 Jun 15;13(6):e0199055. doi: 10.1371/journal.pone.0199055. eCollection 2018.
    PMID: 29906277 Free PMC article."
  • "Protocol for evaluating the effects of a foot-ankle therapeutic exercise program on daily activity, foot-ankle functionality, and biomechanics in people with diabetic polyneuropathy: a randomized controlled trial.Monteiro RL, Sartor CD, Ferreira JSSP, Dantas MGB, Bus SA, Sacco ICN.
    BMC Musculoskelet Disord. 2018 Nov 14;19(1):400. doi: 10.1186/s12891-018-2323-0.
    PMID: 30428863 Free PMC article. Clinical Trial."
  • "Use of local intrinsic muscle flaps for diabetic foot and ankle reconstruction: a systematic review.Ramanujam CL, Stuto AC, Zgonis T.
    J Wound Care. 2018 Sep 1;27(Sup9):S22-S28. doi: 10.12968/jowc.2018.27.Sup9.S22.
    PMID: 30207840"
  • "Intrinsic foot muscle and plantar tissue changes in type 2 diabetes mellitus.Kumar CG, Rajagopal KV, Hande HM, Maiya AG, Mayya SS.
    J Diabetes. 2015 Nov;7(6):850-7. doi: 10.1111/1753-0407.12254. Epub 2015 Mar 24.
    PMID: 25496489 Clinical Trial."
  • "Effects of strengthening, stretching and functional training on foot function in patients with diabetic neuropathy: results of a randomized controlled trial.Sartor CD, Hasue RH, Cacciari LP, Butugan MK, Watari R, Pássaro AC, Giacomozzi C, Sacco IC.
    BMC Musculoskelet Disord. 2014 Apr 27;15:137. doi: 10.1186/1471-2474-15-137.
    PMID: 24767584 Free PMC article. Clinical Trial."
  • "Ultrasound examination of intrinsic foot muscles in patients with 1st metatarsophalangeal joint arthrodesis.Jaffri AH, Hertel J, Saliba S.
    Foot (Edinb). 2019 Dec;41:79-84. doi: 10.1016/j.foot.2019.08.009. Epub 2019 Sep 3.
    PMID: 31739244"
  • "Foot deformities within the diabetic foot and their influence on biomechanics: A review of the literature.Allan J, Munro W, Figgins E.
    Prosthet Orthot Int. 2016 Apr;40(2):182-92. doi: 10.1177/0309364615592705. Epub 2015 Jul 24.
    PMID: 26209425 Review."
  • "Intrinsic foot muscle deterioration is associated with metatarsophalangeal joint angle in people with diabetes and neuropathy.Cheuy VA, Hastings MK, Commean PK, Ward SR, Mueller MJ.
    Clin Biomech (Bristol, Avon). 2013 Nov-Dec;28(9-10):1055-60. doi: 10.1016/j.clinbiomech.2013.10.006. Epub 2013 Oct 12.
    PMID: 24176198 Free PMC article. Clinical Trial."
  • "Toe Flexor Muscle Strength and Morphological Characteristics of the Foot in Judo Athletes.Koyama K, Hirokawa M, Yoshitaka Y, Yamauchi J.
    Int J Sports Med. 2019 Apr;40(4):263-268. doi: 10.1055/a-0796-6679. Epub 2019 Mar 5.
    PMID: 30836392"
  • "Effect of the Intrinsic Foot Muscle Exercise Combined with Interphalangeal Flexion Exercise on Metatarsalgia with Morton's Toe.Yoo WG.
    J Phys Ther Sci. 2014 Dec;26(12):1997-8. doi: 10.1589/jpts.26.1997. Epub 2014 Dec 25.
    PMID: 25540516 Free PMC article."
  • "The effect of stroke on foot kinematics and the functional consequences.Forghany S, Nester CJ, Tyson SF, Preece S, Jones RK.
    Gait Posture. 2014 Apr;39(4):1051-6. doi: 10.1016/j.gaitpost.2014.01.006. Epub 2014 Jan 31.
    PMID: 24548798"
  • "Segmental foot mobility in individuals with and without diabetes and neuropathy.Rao S, Saltzman C, Yack HJ.
    Clin Biomech (Bristol, Avon). 2007 May;22(4):464-71. doi: 10.1016/j.clinbiomech.2006.11.013. Epub 2007 Feb 22.
    PMID: 17320257 Free PMC article."
  • "Muscle weakness and foot deformities in diabetes: relationship to neuropathy and foot ulceration in caucasian diabetic men.van Schie CH, Vermigli C, Carrington AL, Boulton A.
    Diabetes Care. 2004 Jul;27(7):1668-73. doi: 10.2337/diacare.27.7.1668.
    PMID: 15220244 Clinical Trial."
  • "The paper grip test for screening on intrinsic muscle paralysis in the foot of leprosy patients.de Win MM, Theuvenet WJ, Roche PW, de Bie RA, van Mameren H.
    Int J Lepr Other Mycobact Dis. 2002 Mar;70(1):16-24.
    PMID: 12120036"

Runners, Injury Prevention and Flat Feet

Foot intrinsic strengthening is recommended for runners to prevent and heal injuries.

A significant improvement was observed in FPI -6 (talar head palpation in Group 1, and inversion/eversion of the calcaneus in Group 2). Also in Group 1 a significant improvement was noted in FMS tests: deep squat, active straight leg raise and in total score. Conclusions: Short foot muscles strengthening exercises have beneficial effect on functional movement patterns and on foot posture, therefore they should be included as a part of daily training program of runners.

"The Influence of Plantar Short Foot Muscle Exercises on Foot Posture and Fundamental Movement Patterns in Long-Distance Runners, a Non-Randomized, Non-Blinded Clinical Trial.Sulowska I, Oleksy Ł, Mika A, Bylina D, Sołtan J.
PLoS One. 2016 Jun 23;11(6):e0157917. doi: 10.1371/journal.pone.0157917. eCollection 2016.
PMID: 27336689 Free PMC article. Clinical Trial."

The participants were divided into two groups based on baseline measurement of Foot Posture Index: Group 1 (n=27) with neutral foot and Group 2 (n=20) with slight and increased pronation. The participants performed the exercises daily for 6 weeks. The knee flexors and extensors torque, work, and power on Isokinetic Dynamometer and Running-Based Anaerobic Sprint Test (RAST) were checked at baseline and after 6 weeks of exercises. Higher values of peak torque of knee flexors were observed. This change was statistically significant at high load with angular velocity 90°/s (73.55 Nm at baseline and 89.05 Nm after 6 weeks) and 160°/s (69.40 Nm at baseline and 79.00 Nm after 6 weeks) in Group 2. In both groups higher values of maximum power were noted. Participants in Group 2 achieved lower values in each 35-metre run time and higher values of power. In Group 2 there was significant improvement of total time (35.26 s at baseline and 34.79 s after 6 weeks) compared to Group 1 (37.33 s at baseline and 37.56 s after 6 weeks). Exercises strengthening short foot muscles may improve energy transfer through body segments and increase strength and values of generated power. They should be included as a part of daily training programme of runners.

"The Influence of Plantar Short Foot Muscle Exercises on the Lower Extremity Muscle Strength and Power in Proximal Segments of the Kinematic Chain in Long-Distance Runners.Sulowska I, Mika A, Oleksy Ł, Stolarczyk A.
Biomed Res Int. 2019 Jan 2;2019:6947273. doi: 10.1155/2019/6947273. eCollection 2019.
PMID: 30719446 Free PMC article. Clinical Trial."

These findings indicate that in active asymptomatic individuals with over-pronated feet, the foot muscle morphology is adapted to increase control of the foot motion. The morphological characteristics of the foot muscles in asymptomatic individuals with over-pronated feet may affect their foot kinematics and benefit prevention from injuries.

"Comparison of foot muscle morphology and foot kinematics between recreational runners with normal feet and with asymptomatic over-pronated feet.Zhang X, Aeles J, Vanwanseele B.
Gait Posture. 2017 May;54:290-294. doi: 10.1016/j.gaitpost.2017.03.030. Epub 2017 Mar 31.
PMID: 28390293"

  • "Intrinsic foot muscle volume in experienced runners with and without chronic plantar fasciitis.Cheung RT, Sze LK, Mok NW, Ng GY.
    J Sci Med Sport. 2016 Sep;19(9):713-5. doi: 10.1016/j.jsams.2015.11.004. Epub 2015 Nov 22.
    PMID: 26655866"
  • "The Effects of a Transition to Minimalist Shoe Running on Intrinsic Foot Muscle Size.Johnson AW, Myrer JW, Mitchell UH, Hunter I, Ridge ST.
    Int J Sports Med. 2016 Feb;37(2):154-8. doi: 10.1055/s-0035-1559685. Epub 2015 Oct 28.
    PMID: 26509371 Clinical Trial."
  • "Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles.Ridge ST, Olsen MT, Bruening DA, Jurgensmeier K, Griffin D, Davis IS, Johnson AW.
    Med Sci Sports Exerc. 2019 Jan;51(1):104-113. doi: 10.1249/MSS.0000000000001751.
    PMID: 30113521 Clinical Trial."
  • "Foot strength and stiffness are related to footwear use in a comparison of minimally- vs. conventionally-shod populations.Holowka NB, Wallace IJ, Lieberman DE.
    Sci Rep. 2018 Feb 27;8(1):3679. doi: 10.1038/s41598-018-21916-7.
    PMID: 29487321 Free PMC article."
  • "Protocol for evaluating the effects of a therapeutic foot exercise program on injury incidence, foot functionality and biomechanics in long-distance runners: a randomized controlled trial.Matias AB, Taddei UT, Duarte M, Sacco IC.
    BMC Musculoskelet Disord. 2016 Apr 14;17:160. doi: 10.1186/s12891-016-1016-9.
    PMID: 27075480 Free PMC article. Clinical Trial."
  • "The morphology of foot soft tissues is associated with running shoe type in healthy recreational runners.Zhang X, Delabastita T, Lissens J, De Beenhouwer F, Vanwanseele B.
    J Sci Med Sport. 2018 Jul;21(7):686-690. doi: 10.1016/j.jsams.2017.11.008. Epub 2017 Nov 22.
    PMID: 29239782"
  • "Measurement of intrinsic foot stiffness in minimally and traditionally shod runners using ultrasound elastography: A pilot study.Bell EA, Hibbert JE, Domire ZJ.
    J Sports Sci. 2020 Jul;38(13):1516-1523. doi: 10.1080/02640414.2020.1746595. Epub 2020 Mar 30.
    PMID: 32228117"
  • "Management and prevention of bone stress injuries in long-distance runners.Warden SJ, Davis IS, Fredericson M.
    J Orthop Sports Phys Ther. 2014 Oct;44(10):749-65. doi: 10.2519/jospt.2014.5334. Epub 2014 Aug 7.
    PMID: 25103133"
  • "Intrinsic foot kinematics measured in vivo during the stance phase of slow running.Arndt A, Wolf P, Liu A, Nester C, Stacoff A, Jones R, Lundgren P, Lundberg A.
    J Biomech. 2007;40(12):2672-8. doi: 10.1016/j.jbiomech.2006.12.009. Epub 2007 Mar 26.
    PMID: 17368465 Clinical Trial."
  • "Letter to the Editor to the article: The Effects of a Transition to Minimalist Shoe Running on Intrinsic Foot Muscle Size.Robbins S.
    Int J Sports Med. 2016 Oct;37(11):915-6. doi: 10.1055/s-0042-113984. Epub 2016 Sep 29.
    PMID: 27684950 No abstract available."
  • "Surface Stiffness and Footwear Affect the Loading Stimulus for Lower Extremity Muscles When Running.Willwacher S, Fischer KM, Rohr E, Trudeau MB, Hamill J, Brüggemann GP.
    J Strength Cond Res. 2020 Feb 4. doi: 10.1519/JSC.0000000000003410. Online ahead of print.
    PMID: 32028460"
  • "Effects of training in minimalist shoes on the intrinsic and extrinsic foot muscle volume.Chen TL, Sze LK, Davis IS, Cheung RT.
    Clin Biomech (Bristol, Avon). 2016 Jul;36:8-13. doi: 10.1016/j.clinbiomech.2016.05.010. Epub 2016 May 10.
    PMID: 27195735 Clinical Trial."

Literature on Intrinsic Muscle Theory

Intrinsic muscle theory is an established method to understanding foot function.

The human foot is renowned for its ability to recycle mechanical energy during locomotion, contributing up to 17% of the energy required to power a stride. This mechanism has long been considered passive in nature, facilitated by the elastic ligaments within the arch of the foot. In this paper, we present the first direct evidence that the intrinsic foot muscles also contribute to elastic energy storage and return within the human foot. Isometric contraction of the flexor digitorum brevis muscle tissue facilitates tendon stretch and recoil during controlled loading of the foot.

"Intrinsic foot muscles contribute to elastic energy storage and return in the human foot.Kelly LA, Farris DJ, Cresswell AG, Lichtwark GA. J Appl Physiol (1985). 2019 Jan 1;126(1):231-238. doi: 10.1152/japplphysiol.00736.2018. Epub 2018 Nov 21. PMID: 30462568"

The results suggest that the architecture and contraction time of the FDB reflect its unique direct contribution, through toe flexion, to postural stability and the rapid development of ground reaction forces during forceful activities such as running and jumping.

"The architecture and contraction time of intrinsic foot muscles.Tosovic D, Ghebremedhin E, Glen C, Gorelick M, Mark Brown J.
J Electromyogr Kinesiol. 2012 Dec;22(6):930-8. doi: 10.1016/j.jelekin.2012.05.002. Epub 2012 Jun 27. PMID: 22742974"

Furthermore, we believe that intrinsic foot flexor strength training is useful for improving standing and walking performance, in addition to improving the performance of sports athletes engaged in activities involving greater exercise loads.

"Strength training for the intrinsic flexor muscles of the foot: effects on muscle strength, the foot arch, and dynamic parameters before and after the training.Hashimoto T, Sakuraba K. J Phys Ther Sci. 2014 Mar;26(3):373-6. doi: 10.1589/jpts.26.373. Epub 2014 Mar 25. PMID: 24707086 Free PMC article."

  • "Common Foot Problems: Over-the-Counter Treatments and Home Care. Becker BA, Childress MA. Am Fam Physician. 2018 Sep 1;98(5):298-303.
    PMID: 30216025 Review."
  • "Does neuromuscular electrostimulation have the potential to increase intrinsic foot muscle strength?Ebrecht F, Sichting F. Foot (Edinb). 2018 Jun;35:56-62. doi: 10.1016/j.foot.2018.01.006. Epub 2018 Jan 31. PMID: 29803167"
  • "Effects of a 4-Week Intrinsic Foot Muscle Exercise Program on Motor Function: A Preliminary Randomized Control Trial.Fraser JJ, Hertel J.
    J Sport Rehabil. 2019 May 1;28(4):339-349. doi: 10.1123/jsr.2017-0150. Epub 2018 Dec 4. PMID: 29364026 Clinical Trial."
  • "Intrinsic foot muscle size can be measured reliably in weight bearing using ultrasound imaging. Franettovich Smith MM, Hides JA, Hodges PW, Collins NJ.
    Gait Posture. 2019 Feb;68:369-374. doi: 10.1016/j.gaitpost.2018.12.012. Epub 2018 Dec 6. PMID: 30583193"
  • "Firing properties of muscle spindles supplying the intrinsic foot muscles of humans in unloaded and freestanding conditions.Knellwolf TP, Burton AR, Hammam E, Macefield VG. J Neurophysiol. 2019 Jan 1;121(1):74-84. doi: 10.1152/jn.00539.2018. Epub 2018 Nov 14. PMID: 30427762"
  • "The relationship between foot posture and lower limb kinematics during walking: A systematic review.Buldt AK, Murley GS, Butterworth P, Levinger P, Menz HB, Landorf KB. Gait Posture. 2013 Jul;38(3):363-72. doi: 10.1016/j.gaitpost.2013.01.010. Epub 2013 Feb 5. PMID: 23391750 Review."
  • "Intrinsic foot joints adapt a stabilized-resistive configuration during the stance phase.Deleu PA, Chèze L, Dumas R, Besse JL, Leemrijse T, Devos Bevernage B, Birch I, Naaim A. J Foot Ankle Res. 2020 Mar 12;13(1):13. doi: 10.1186/s13047-020-0381-7. PMID: 32164783 Free PMC article."
  • "The foot is more than a spring: human foot muscles perform work to adapt to the energetic requirements of locomotion.Riddick R, Farris DJ, Kelly LA.
    J R Soc Interface. 2019 Jan 31;16(150):20180680. doi: 10.1098/rsif.2018.0680.
    PMID: 30958152 Free PMC article. Clinical Trial."
  • "The functional importance of human foot muscles for bipedal locomotion.Farris DJ, Kelly LA, Cresswell AG, Lichtwark GA.
    Proc Natl Acad Sci U S A. 2019 Jan 29;116(5):1645-1650. doi: 10.1073/pnas.1812820116. Epub 2019 Jan 17. PMID: 30655349 Free PMC article."
  • "Importance and challenges of measuring intrinsic foot muscle strength.Soysa A, Hiller C, Refshauge K, Burns J. J Foot Ankle Res. 2012 Nov 26;5(1):29. doi: 10.1186/1757-1146-5-29. PMID: 23181771 Free PMC article."
  • "Comparison of foot kinematics and the morphology of intrinsic musculature of the foot using a foot-type classification based on function.Kudo S, Sakamoto K, Shirakawa T. J Phys Ther Sci. 2020 Mar;32(3):238-242. doi: 10.1589/jpts.32.238. Epub 2020 Mar 11. PMID: 32184540 Free PMC article."
  • "Congenital hypertrophy of multiple intrinsic muscles of the foot.Shiraishi T, Park S, Niu A, Hasegawa H. J Plast Surg Hand Surg. 2014 Dec;48(6):437-40. doi: 10.3109/2000656X.2013.812765. Epub 2013 Jul 4. PMID: 23822188 Review."
  • "Quantitative analysis of the intrinsic muscles of the foot.Kura H, Luo ZP, Kitaoka HB, An KN. Anat Rec. 1997 Sep;249(1):143-51. doi: 10.1002/(SICI)1097-0185(199709)249:1<143::AID-AR17>3.0.CO;2-P. PMID: 9294659"
  • "Reliability of doming and toe flexion testing to quantify foot muscle strength.Ridge ST, Myrer JW, Olsen MT, Jurgensmeier K, Johnson AW.
    J Foot Ankle Res. 2017 Dec 8;10:55. doi: 10.1186/s13047-017-0237-y. eCollection 2017. PMID: 29234467 Free PMC article."
  • "Behavioral implications of ontogenetic changes in intrinsic hand and foot proportions in olive baboons (Papio Anubis).Druelle F, Young J, Berillon G.
    Am J Phys Anthropol. 2018 Jan;165(1):65-76. doi: 10.1002/ajpa.23331. Epub 2017 Oct 27. PMID: 29076148"
  • "Physical signs of the intrinsic minus foot.Bernstein RK.
    Diabetes Care. 2003 Jun;26(6):1945-6. doi: 10.2337/diacare.26.6.1945. PMID: 12766145 No abstract available."
  • "The Intrinsic Muscles of the Mammalian Foot.Cunningham DJ.
    J Anat Physiol. 1878 Oct;13(Pt 1):1-16. PMID: 17231225 Free PMC article. No abstract available."
  • "The mechanics behind the image: foot and ankle pathology associated with gastrocnemius contracture.Bowers AL, Castro MD.
    Semin Musculoskelet Radiol. 2007 Mar;11(1):83-90. doi: 10.1055/s-2007-984418. PMID: 17665354 Review."
  • "THE ACTION OF THE INTRINSIC MUSCLES OF THE FOOT AND THEIR TREATMENT BY ELECTRICITY.Levick GM.
    Br Med J. 1921 Mar 12;1(3141):381-2. doi: 10.1136/bmj.1.3141.381. PMID: 20770217 Free PMC article. No abstract available."
  • "Congenital hypertrophy of an intrinsic muscle of the foot.Estersohn HS, Agins SW, Ridenour J. J Foot Surg. 1987 Nov-Dec;26(6):501-3. PMID: 3446705"
  • "Variable innervation of the intrinsic foot muscles. An electrophysiological study.Linden D, Glocker FX, Berlit P. Electromyogr Clin Neurophysiol. 1996 Oct-Nov;36(7):399-403. PMID: 8957164"