The plantar intrinsic foot muscles might be the most underestimated players in the quest for optimizing posture and ideal function. These muscles are instrumental in controlling the dissipation of ground forces and stabilizing the foot during impact. Likewise, afferent inputs from the sole of the foot are believed to affect postural awareness and gait. It stands to reason that improving the function of the intrinsic foot muscles may be one of the best ways to promote ideal stabilization and motor control throughout the entire body. The following is a review of the basics of the intrinsic foot muscles (IFM), the implications of imbalance in the IFM and a discussion of Janda's short foot exercise.

Anatomy and Function

The plantar IFM are arranged in four layers, all of which are innervated by the plantar branches of the tibial nerve. The first layer consists of the abductor hallucis (often celebrated as the captain of the IFM), flexor digitorum brevis and the abductor digiti minimi. The second layer includes the quadratus plantae and the lumbricals; the third layer includes the adductor hallucis transverse, adductor hallucis oblique, flexor hallucis brevis and flexor digiti minimi brevis. The fourth layer includes the interossei muscles. The plantar IFM differ from their more extrinsic foot counterparts in that they strictly span the foot and do not cross the ankle. Their primary function is to provide dynamic support of the medial longitudinal arch (MLA) of the foot and to control forces that act to excessively spread the arch while walking, running or jumping.

The MLA consists of the calcaneus, talus, navicular, cuboid, three cuneiforms and the first three metatarsals. Many conceptualize these bones as fixed; however, there should be a fair amount of rotation, flexion and extension occurring between these structures during impact and push off phases of gait, as this mobility is necessary for additional shock absorption and force generation. While many foot structures contribute to the static and dynamic control of the MLA, the intrinsic foot muscles may be the most important. A study by Fiolkowski et al 2003, discovered a significant navicular drop (the keystone of the MLA) after administering a nerve block in order to de-activate the intrinsic muscles in study participants. Another study by Headlee et al 2008, induced fatigue to the IFM and also discovered a significant navicular drop. Both of these studies indicate the essential role of the IFM in supporting the MLA and suggests that IFM weakness can contribute to an unstable, poorly functioning foot.

IFM Imbalance Implications

Although difficult to isolate the IFM during testing, weakness in these muscles have been associated with many foot and ankle problems including plantar fasciitis, lesser toe deformities and bunions. Weakness of the intrinsic foot muscles is considered a risk factor for plantar ulcerations in individuals suffering from diabetes. This is likely due to the altered foot rollover during gait and ineffective plantar load distribution. Imbalance in these muscles is not simply a local issue, as faulty foot mechanics are known to cause compensations up the kinetic chain leading to knee, hip, low back and cervical issues.

How about just going for a barefoot run to train the IFM? I'm often asked if minimalist footwear or going sans shoes is a good way to correct poorly functioning feet. As Gray Cook would probably say,"don't add strength to dysfunction." The problem I have with our clients ditching their clunky running shoes is that their feet are not prepared for the demands of their body weight meeting the ground without a nice cushioned buffer. It is my opinion that some feet just don't have the potential to go completely naked; those that do will need to improve the function of the intrinsic foot muscles and progressively strengthen the musculature before they begin wearing the minimalist footwear or going barefoot for extended periods of time. In other words, running barefoot or wearing minimalist shoes are the end game, not the place to start. Janda believed that the proprioceptors on the sole of the foot need to be stimulated and a balance of activity among the intrinsic and extrinsic muscles of the foot needs to be established in order for lasting positive change can occur. So our "restore the foot project" should begin with a combination of appropriate soft tissue work and sensory motor retraining and maybe somewhere down the road, our clients can let their feet run naked. As always, consider the entire body when doing your evaluation and assessments.

Assessment

As much as I like simple assessments, the old "wet foot test" probably doesn't reveal all that much in terms of what we need to do to help our clients reclaim functional feet. Although many would say the SFE is well suited to the flat foot (pes planus), those with high arches (pes cavus) and neutral arches can collapse just as much as the structurally flat foot during dynamic foot movements. Along these same lines, all arch sizes are subject to issues such as plantar fasciitis, achilles tendonopathy, tibialis anterior and posterior overuse syndromes, stress fractures, etc. This has led many researchers and clinicians to suggest that these commonly seen overuse pathologies may be a result of the client lacking the ability to control the arch upon landing and pushing off rather than just having a puny arch. So, if our goal is to improve the ability of these muscles to dynamically control the MLA, we need to see the client's feet in action. I use two dynamic assessments, which are not meant to take the place of a thorough exam by a foot specialist, but it will give you an idea of if the IFM are adequately controlling the MLA.

Walking test. Without the client's knowledge, observe the way they walk toward you (you will get a more accurate impression of their foot control if they don't know you are critically assessing them). A few things you want to look out for:

• Excessive collapse of the MLA at mid-stance or continued pronation of the foot at heel lift.
• Everted front foot at mid-stance.
• Valgus collapse of the knee.
• Foot seems to stay in contact with the ground a little to long.
• Note any movement asymmetry from right to left.

Single leg test. Have the client stand facing a wall, with the feet and knees shoulder width apart, with the knees slightly flexed. The client should place their finger tips on the wall for a bit of balance help. Instruct the client to gently supinate the feet by lifting their toes (this will wind the plantar fascia and create an arch), then slowly drop the toes but try to maintain the arch that was created. If they can't do this on their own, you can help by placing your hands on their foot and actively shortening their foot for them. While holding the MLA, have the client lift one foot and stand on one leg for 30 sec. Note the steadiness of the client and watch for any reduction in the MLA. Keep a look out for excessive toe grabbing; this is considered faulty patterning and demonstrates a dominance of the more extrinsic muscles of the foot and ankle. Have them perform the same test on the other foot.

If you observed any the faulty patterns mentioned above, the SFE is likely a good corrective exercise for them.

Towel Grab vs. Short Foot Exercise

I admit, I used to love the towel grabbing exercise for my weak footed clients; as it turns out, it may not have been the best IFM strategy. Recent research pitted the towel grab exercise against the SFE with the researchers concluding that the SFE is more effective at recruiting the IFM. Despite these results, don't ditch your towels, just save them for the clients with weak, unstable ankles.

I find the best time to work the SFE into a session is after bodywork. Specifically after I've done some big toe mobilization and myofascial work on the feet. When your clients first attempt the SFE, they will likely have no sense of how to turn on these intrinsic muscles, this will be seen by the client grabbing the ground with the toes. This lack of motor control will require your assistance to model what the foot should do. With your client seated, place one of your hands on the back of the client's heel, while the other hand should cup the forefoot. Gently squeeze the 1st and 5th metatarsals together while creating a supportive pressure to the back of the heel. Your intention is to condense their foot, which should create a neutral arch for them. Ask your client to feel what is happening to their foot and to try and appreciate the energy it would take to hold this foot posture.

With your hands on the client's foot, have them actively hold the arch, assist them with some tactile support when you note a failure of proper foot activation. Cue the client to narrow the forefoot and pull the front of the foot toward the heel. They should be able to create an arch while the toes and heels remain flat on the floor and the toes are not excessively grabbing the floor. Once the client has developed a feel of what the short foot feels like, keep them seated but wean them from your help by taking your hands away and have them hold the short foot for 10 seconds followed by a short rest, then repeat 4-5 times. The next progression is to perform the SFE while standing, once again challenging them to hold the short foot for 10 sec and then resting and repeating 4-5 times.

As these muscles get stronger and more adept at firing, have them hold the short foot for longer intervals. Eventually have the client integrate their new and improved "short foot" to more functional activities such as performing a squat-single leg standing while touching a wall for support (single leg standing without the wall) performing a lunge, etc.

The SFE may be one of the best ways to re-establish control of the intrinsic foot muscles. These muscles are known to have a positive influence on posture and gait, yet are often times "out to lunch" regardless of foot type. Soft tissue work in addition to improving motor control of the foot will go a long way to restoring muscular balance, optimizing posture and preventing injury.

Resources:

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