Heel pain can be caused by multiple different pathologies, the most common one being plantar fasciitis. The plantar fascia is a thick fibrous band on the underside of the foot that runs on the underside of your foot from the calcaneus (your heel bone) towards the toes. The plantar fascia, intrinsic muscles of the foot and the toe flexor muscles function together to allow the foot to be flexible enough to act as a shock absorber and to create stiffness in the foot to allow for efficient walking or running. When one of these structures in the foot doesn’t function the way it should, the biomechanics of the foot are altered which places additional stress on other tissues.
As musculoskeletal clinicians, we’ve been quick to blame flat feet or an overpronated foot as the primary cause of plantar fasciitis. Why did we pin the blame on a flat foot? It was thought that an overpronated or flat foot placed an increased tensile load on the plantar fascia eventually leading to disruption and inflammation of the collagen fibres. Plantar fasciosis is the correct term for this condition as there is disruption of the collagen fibres but there are no inflammatory cells present in the tissue. We’ve discussed this topic in another blog post which you can read by clicking here. In this post this blog post I’ll continue referring to the condition as plantar fasciitis.
Are Orthotics Effective For Plantar Fasciitis?
Orthotics have become a popular treatment option for plantar fasciitis. The theory was that if you maintain the medial arch height of the foot, tensile loads placed on the plantar fascia will be reduced. However, research done by Wearing et al. shows that orthotics are not effective for managing plantar heel pain as there is a poor correlation between low arch height and the development of plantar fasciitis.
What the authors discovered was that the best predictor for the development of plantar fasciitis was the speed at which the toes dorsiflexed during the propulsive motion.
The toe flexor muscles actively contract to help control toe dorsiflexion. Weakness of these muscles can result in the toes moving through an excessive range of motion during walking or running which increases the tensile load on the plantar fascia.
What Physical Causes Could Increase The Risk Of Plantar Fasciitis?
A study was done by Sullivan et al in 2015 where they took 202 people with plantar heel pain and compared them to 70 “normal” people without heel pain. They compared a range of potential physical causes such as:
Out of all the potential causes, the authors found three physical differences between the group with plantar heel pain and those without. They were:
These three physical factors should always be addressed in a plantar fasciitis rehabilitation program. In this post, I’ll just be discussing ways to strengthen the toe flexor and peroneal muscles. If you would like to learn more about improving ankle range of motion, it’s been covered in another blog post which you can access here.
How To Test The Muscles Of The Foot
Testing the strength of the toe flexor muscles provides a good baseline that we can refer back to throughout the rehabilitation process. The test that we use is called the paper grip test. We use a force gauge with a rigid piece of plastic attached that’s about the size of a business card. We instruct our patients to keep their knees bent to 90 degrees, heel flat on the floor and to resist the card from being pulled from under their toes by pressing their toes down onto the card as hard as they can.
The 1st toe is tested on its own and the 2nd to 5th toes are tested together. That is because flexion of the 1st toe is controlled by the flexor hallucis longus and flexor hallucis brevis muscles. The 2nd – 5th toes are flexed by the flexor digitorum longus and flexor digitorum brevis muscles.
This is a view from underneath the feet looking at the heels. The flexor digitorum longis and flexor digitorum brevis muscles have been selected. They’re responsible for toe flexion of the 2nd-5th toes. The flexor hallucis longis and flexor hallucis brevis muscles are hilighted on the right foot. They control flexion of the 1st toe
The test is repeated three times and we record the maximum amount of force needed to pull the card from under their toes. An adult male should be able to generate a force under their 1st toe equal to 10% body weight, and around to 7% body weight under the 2nd to 5th toes.
How To Strengthen The Muscles Of The Foot
The most effective way to strengthen the muscles of the foot is to train the toe flexor and peroneal muscles in a lengthened position. That is because it replicates the positions these muscles will be in during walking or running.
The peroneal muscles run along the side of your shin to the underside of your foot. A particularly important muscle is the peroneus longus because it attaches to the base of the 1st metatarsal and assists with depressing the 1st metatarsal while weight-bearing. By doing so it helps to offload the medial part of the plantar fascia and reduces the tensile force on your calcaneus (heel bone) where the plantar fascia attaches.
Take note of where the peroneus longus muscle runs. In the second image the other structures have been faded.
To rehabilitate the foot we use a device called a ToePro. It’s a foam structure with specific angulations and ridges that places the toe flexor and peroneal muscles in a lengthened position. If you’re in Australia you can order one from www.mytoepeo.com.au or pick one up from our clinic in Brisbane. Alternatively, you can use a rolled-up yoga mat placed underneath your foot to get these muscles into their lengthened position.
Theraband toe flexion exercises have been used in the past to isolate and strengthen the intrinsic muscles of the foot. The issue with these exercises is that the toe flexor muscles are trained in their shortened position which means that if there are any strength gains, they won’t translate into significant improvements in force production in a functional (lengthened) position.
Exercise #1
This is a good warm-up exercise. The key here is to first push your toes down hard into the mat or ToePro. Then shift your weight forward towards the wall allowing your ankles to dorsiflex slightly while maintaining your toe contraction. Hold for 3 seconds and slowly return to the start position.
Recommended: 20 Repetitions.
Exercise #2
Move your foot up the toe pro so that your toes are positioned over the ridge on the top of the platform. This gets a bit tricker if you’re using a yoga mat. If you’re using a ToePro, the angulation of the device will cause your foot to invert which places the peroneal muscles in a lengthened position. Press your toes down hard into the platform again, shift your weight from the outer part of your foot towards your first toe and press up into a calf raise. Lower back down to the ground and repeat.
This exercise can also be performed with your knees slightly bent to target the soleus muscle.
Recommended: 25 repetitions
Exercise #3
This single-leg variation focuses on the peroneal muscles as the foot is placed in an exaggerated inversion position. Start the movement by pressing your toes down hard into the mat or toe pro. Shift your weight from the other part of your foot towards the inner part and forwards towards your big toe. Press up into a calf raise and then lower back down again.
This exercise can also be performed with a slight knee bend.
Recommended: 25 repetitions
Exercise #4
This single-leg variation places the foot in an everted position, meaning that a muscle called the tibialis posterior is placed in a lengthened position. The tibialis posterior runs behind the shin and under the medial arch of your foot. Press your toes down hard into the mat or ToePro device and press up into a calf raise.
This exercise can also be performed with a slight knee bend.
Recommended: 25 repetitions
Conclusion
The toe flexor and peroneal muscles play an important role in distributing force throughout the foot. A failure of these muscles to decelerate the toes during the propulsive phase of walking or running places increased stress on the plantar fascia which can lead to tissue breakdown and pain.
It’s important that any plantar fasciitis rehabilitation program the aim is to restore normal ankle range of motion and to improve the strength of the toe flexor and peroneal muscles as these three factors are the biggest physical differences between people with and without plantar fasciitis.
About the author:
Dr Michael Benporath is a chiropractor with a postgraduate International Certificate in Sports Chiropractic. He practices at Prime Health Co. in Newmarket, Brisbane Northside.
