Plantar Fasciitis Sufferers Have Weaker Foot Muscles

Toe flexors strength and passive extension range of motion of the first metatarsophalangeal joint in individuals with plantar fasciitis. J Orthop Sports Physical Therapy. 2003 Aug;33(8):468-78. Allen RH, Gross MT.

Abstract
STUDY DESIGN:
Cross-sectional study.
OBJECTIVE:
To determine if a difference exists in toe flexors strength and passive extension range of motion of the first metatarsophalangeal joint between individuals with unilateral plantar fasciitis and control subjects.
BACKGROUND:
Weakness of the dynamic longitudinal arch supporters and shortening of the plantar fascia have been suggested as etiologic factors for plantar fasciitis. METHOD AND MEASURES: Twenty subjects with unilateral plantar fasciitis participated in the study. Subjects had had symptoms for an average (+/-SD) of 19.9 +/- 33.2 months prior to participating in the study. Twenty control subjects matched for sex and age were also tested. Each subject was measured bilaterally for passive extension range of motion of the first metatarsophalangeal joint and peak resistance force observed during an isometric test of toe flexors strength.
RESULTS:
Subjects with unilateral plantar fasciitis demonstrated weaker toe flexors (P<.05) than the control subjects. A significant main effect for feet also indicated that the toe flexors for the involved feet were significantly weaker than the uninvolved feet (P<.05) of subjects with unilateral plantar fasciitis. Passive extension range of motion of the first metatarsophalangeal joint was not significantly different between the involved and the uninvolved feet for subjects with plantar fasciitis.
CONCLUSION:
Results for our subjects indicate that the extensibility of soft tissues influencing extension of the first metatarsophalangeal joint was not related to the presence of plantar fasciitis. Additional research is needed to determine if toe flexors weakness is a cause or a result of plantar fasciitis and if strengthening regimes for the toe flexors are effective interventions for plantar fasciitis.

My comments:

This study is over 10 years old (my next planned blog is even older) and I find it interesting how you often have to look back into the history of research to come up with something new or better. What these researchers found was that the plantar fascia was NOT tight (as measured by toe extension). However, toe flexor muscle strength in those with plantar fasciitis was weak, with the painful foot being able to flex with 88 Newtons (N) of force compared to 96 N on their non-painful side. What’s more was that both the painful and non-painful foot was weak as compared with normal control subjects without pain, whose toe flexion strength ranged from 117-135 N. This tends to confirm the suspicions I had with regard to foot intrinsic muscle atrophy in an earlier blog on plantar fasciitis that found muscle atrophy in the painful foot in comparison to the non-painful foot, but did not compare to normal controls. This study shows that muscle weakness is worse on the painful side and worse still in comparison to normal controls, such that one might reasonably assume the same with muscle atrophy.

The conclusion I am reaching, and using successfully in my physical therapy office, is that though the plantar fascia is technically a ligament, it has many similarities with tendinopathy and should be treated as such. Some stretch is likely still important, but a much greater emphasis should be placed on strengthening the muscles within the foot as well as outside through a combination of progressive resistance exercise and electric muscle stimulation.  Muscle weakness being much of the problem would explain why both OTC and custom orthotics have such little effect on plantar fasciitis.

Thanks for reading my blog. If you have any questions or comments (even hostile ones) please don’t hesitate to ask/share. If you’re reading one of my older blogs, perhaps unrelated to neck or back pain, and it helps you, please remember SpineFit Yoga for you or someone you know in the future.

Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.