Heel Lifts - Anatomical versus Functional Leg Length Discrepancy


Have you been told you need a heel lift? Have you been diagnosed with Scoliosis or a Leg Length Discrepancy? Have you been told your hips aren’t level, or one shoulder is higher than the other? Take a look at your arches. If one arch is significantly lower than the other, chances are that your feet are trying to compensate for a problem that could be related to your hips but can also be an Anatomical Leg Length Discrepancy.

Before you start wearing a heel lift in one shoe, let’s explore the root cause of what might be happening with your muscles and bones.
A difference in leg length causes pelvic instability. For people with an Anatomical Leg Length Discrepancy, the bones are uneven lengths, and this is most accurately documented by taking appropriate x-rays. Heel lifts are helpful when the ALLD is relatively small. If your ALLD is minimal, you can use our separately packaged Heel Lifts. They are made of polyurethane and measure 3mm each. They are sold in pairs, and are designed to be worn underneath the ProKinetics insole, in the bottom of the shoe, not next to the foot. You would start with ½ the discrepancy, building up to the full ALLD, but if it is over 1/4 - 3/8 inch the whole shoe should be built up from heel to toe.

Contains 2 heel lifts and achesive.


Functional Leg Length Discrepancy (FLLD)   •   •   •   •   •   • 

When a practitioner has you lay down on the examining table and pulls your feet to see if your legs look the same length, this may confirm you have a difference in your leg lengths, BUT, the bones may be the same length. What is happening? This is very common for people who overpronate. The muscles on one side of your body are often stronger, or tighter than on the other. It may cause misalignments in the spine that can be adjusted, but once you stand up, you go out of adjustment again.

One foot oftentimes pronates more than the other. When this occurs, it performs as if it’s shorter than the other because the arch falls in and the knee moves inward more on one side than the other. This is more specifically diagnosed as a “Functional Leg Length Discrepancy”, and is muscle related not bone related because the body tries to compensate.

A good way to check if you may have a functional Leg Length Discrepancy is to test yourself for over pronation.

Up to two lifts can be placed in one shoe, compensating for a 1/4 in Anatomical Leg Length Discrepancy (ALLD).

Anatomical Leg Length Discrepancy (ALLD) should be established by x-ray to actually make direct measurements. Estimates by observation either standing or lying down is inaccurate and is more likely to reflect a Functional Leg Length Discrepancy (FLLD).

Test Yourself

When testing yourself to determine how much you over pronate, you will also discover why you pronate.

This exercise simulates what happens when you walk, and is an approximation of how much you structurally over pronate.  This is most easily done in front of a long mirror or with the assistance of a friend. 

Step 1

First, stand on a hard surface with your feet comfortably apart, toes straight forward and feet parallel.  Lean slightly forward and bend your knees so that your hips drop 8-10 inches straight down. Don't squat, and keep your heels on the ground. 

Your knees should neither move inward (medially) nor outward (laterally) when you bend them, so if you have to, force your knees to move straight forward so they are alighed with the middle of your feet (third toes).

Next, from this position, move your knees slowly toward each other until you feel full weight bearing pressure under the balls of your feet behind your big toes. Not all the pressure, but at least as great as anywhere else under the foot.

Next, with knees in that position, draw an imaginary line from the middle of your knee straight down to the ground (the blue line in the picture)

6.0 mm:  If the line touches your feet in the orange range, you will do best with 6.0 mm Ultra Thin Insoles or add the orange wedge to your ProKinetics® Replacement Insoles. 

3.5 mm:  If the line touches your feet in the red zone you will most likely do well with 3.5 mm Ultra Thin Insoles or without adding the orange wedge to your ProKinetics® Replacement Insoles. 

Step 2

The wear pattern of your shoes indicate how you respond to your own structural pronation (what you just measured).

Over 60% of people who over pronate need to start in 3.5 mm insoles and graduate to 6.0 mm later. 
You are in this group if you tend to have an outside heel strike with a wear pattern that tracks forward on the outside heel and if you have a middle to outside wear pattern in the forefoot.

If in doubt, you can purchase the Perfect Fit™ which like the ProKinetics, contains all the components you need to start conservatively and graduate to more Kinetic Technology™ (forefoot wedge) if you need it. 

Rule of Thumb: If your shoes wear hardest from the middle toward the outside edge, you should always start in 3.5 mm or the red wedge. If you wear your shoes hardest from the middle toward the inside edge of your shoes, and if the knee bend test indicates you need 6.0 mm, you can start with 6.0 mm or the orange wedge. When in doubt, always be conservative. This is a technology where more is not better unless you actually need it.

The orange wedge attaches on top to provide 6.0 mm correction.

Stand with feet parallel and do a 1/4 knee bend.

Observe how far the knees have to move inward in order for the inside of the foot to become weight bearing.

If your wear pattern looks like any of these you will do best starting with 3.5 mm insoles and go to 6.0 mm after 7-10 days.

If your wear pattern looks more like this, you can start directly with 6.0 mm correction if needed.

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Getting to the root cause

If all your metatarsals and toes are on the ground, figure A, you'd be balanced and your arch would be stable--not dropping.  The problem is that for most people, the big toe (and first metatarsal) h Morton's Foot Syndrome (shortened first metatarsal and deeper first web space).  It is an issue of the bones in the foot - specifically the head of the Talus (ankle bone).  Because of an upward rotation of the head of the Talus, the first metatarsal and the big toe literally have to travel a small distance toward the ground to become weight bearing, and in the process the inside of the foot, the arch, collapses. 

The elevated first metatarsal also causes the ankle to roll in and an internal rotation of the leg.  You were born with the elevated first metatarsal which greatly impacts your gait and posture. 

The muscles controlling your arches were stronger when you were younger and more active. By the same token, children today are less active and weaker, and as a result, they suffer with back aches and other musculoskeletal pain in record numbers.  Most people try to control their arches using the wrong muscles - we call them “bracers”  because they brace their muscles against hyperpronation.  That leads to tired calf muscles and shin splints.  We know with certainty that faulty foot mechanics and poor posture catches up with you as you age.  By the age of 40, most people suffer from some kind of foot and posture related musculoskeletal pain.   


Fig A. All the toes should be on the ground.


The elevated first metatarsal seen in the frontal plane

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ProKinetics® Posture Control Insoles®

When you pick up a towel from the floor with your feet, you bring your first metatarsal and big toe down to the ground so your foot can be properly supported.  That is exactly what Posture Control Insoles® do - bring your first metatarsal and big toe down to the ground.  Simply put, Posture Control Insoles® put that foot exercise you did "on automatic" with every step - they help your body heal itself.  The insoles allow your body to correct your gait and posture.  Your performance will improve, your muscles will relax and your pain will subside.  It doesn't happen instantaneously, but after 7-10 days you should feel a significant difference. 

That is our guarantee.  In fact, if you are not satisfied with the results, we will refund your entire purchase price including *shipping and handling. 


*limited to standard shipping by priority mail. 

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Getting Started

The ordering process is simple.  Two quick evaluations will tell you exactly what Posture Control Insoles® to buy. 

  • Check your shoe wear pattern

  • Check your foot mechanics

We'll show you exactly how.  Click to proceed with your "2 minute evaluation".

Would you rather just test them in your shoes?  You'll have what you need with the Perfect Fit™ package giving you both the 3.5 mm and the 6.0 mm pair - the second pair at a 40% discount. 

Relief in just a few days: Start by choosing Gender and Size.


*Choose#1 (low) Arch for flat feet and mild Plantar Fasciitis.  Choose #2 (high) Arch for severe Plantar Fasciitis. Otherwise choose NO arch support.


Perfect Fit™
$70.00 + S&H


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