Category: Biomechanics

Supination Resistance

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Supination Resistance is a concept of determining the force needed to supinate the foot. This is considered important in foot orthotic prescribing as it is helpful to determine how much force if needed from the foot orthotic if the foot is overpronating.

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Supination resistance refers to the amount of force required to supinate (invert) the foot around the subtalar joint during gait or clinical testing. It’s a key concept in biomechanics and podiatry, because it helps clinicians understand how easily or how much effort it takes for a person’s foot to resupinate during walking or running. Normally, after the foot pronates during stance phase (to absorb shock and adapt to the ground), it needs to resupinate for effective propulsion. If the foot has high supination resistance, it means a lot of force is required to achieve this motion, potentially leading to inefficient gait mechanics and increased risk for overuse injuries.

Several factors influence supination resistance, including the alignment of the subtalar joint, midtarsal joint mobility, body weight, and even soft tissue flexibility. For instance, individuals with a medially deviated subtalar joint axis often have higher supination resistance because ground reaction forces act more medially, increasing the lever arm for pronatory forces. Conversely, someone with a more laterally placed subtalar axis may have lower resistance. Clinically, high supination resistance is often associated with persistent pronation, flat feet (pes planus), and conditions like posterior tibial tendon dysfunction, while low supination resistance may correlate with rigid high-arched feet (pes cavus) that don’t adapt well to ground surfaces.

Understanding supination resistance is important for treatment planning, especially when prescribing foot orthotics. Patients with high supination resistance may need orthotics that provide more aggressive arch support or medial posting to control pronation. On the other hand, for those with low resistance, excessive correction can actually destabilize the foot. Some clinicians use devices like a supination resistance meter, but often manual testing provides sufficient clinical information. Ultimately, evaluating supination resistance helps personalize interventions, optimize gait, and reduce injury risk.

Most Useful Resources:
https://podiapaedia.org/wiki/biomechanics/clinical-biomechanics/concepts/supination-resistance/ (PodiaPaedia)
https://podiatryarena.com/index.php?articles/supination-resistance.1/ (Podiatry Arena)
https://podiatryarena.com/index.php?tags/supination-resistance/ (Podiatry Arena)
http://www.runresearchjunkie.com/the-concept-of-supination-resistance/ (Running Research Junkie)
http://www.podiatryfaq.com/supination-resistance/ (Podiatry FAQ)
http://www.ipodiatry.org/the-concept-of-supination-resistance/13688 (iPodiatry)

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Jacks Test

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Jacks Test is a test of how hard it is to dorsiflex the hallux when weightbearing, so is a test of the integrity of the windlass mechanism. It is known at the Hubscher maneuver in the USA

Jack’s test is a clinical examination used to assess the function of the medial longitudinal arch of the foot, particularly in evaluating for flexible flatfoot (pes planus). It is also known as the “Hubscher maneuver.” The test is typically performed while the patient is standing. The examiner dorsiflexes the big toe (hallux) while observing changes in the arch of the foot. A positive result is indicated by the formation of an arch when the big toe is dorsiflexed, suggesting that the flatfoot is flexible and not rigid.

This test is based on the windlass mechanism of the foot. Dorsiflexion of the big toe tightens the plantar fascia, pulling the heel and the ball of the foot closer together and raising the arch. In a patient with a functional (flexible) flatfoot, this mechanism remains intact, and the arch reappears when the toe is lifted. However, in cases of rigid flatfoot, the arch remains flat despite dorsiflexion of the toe, indicating a more serious structural problem that may require orthopedic intervention.

Jack’s test is a simple yet valuable tool for distinguishing between flexible and rigid flatfoot, helping clinicians guide treatment strategies. Flexible flatfoot is often managed conservatively with physical therapy, orthotics, or footwear modification, while rigid flatfoot may necessitate more invasive interventions. Jack’s test can also be useful in pediatric assessments, as flatfoot is common in children and often resolves with age. By providing insight into foot mechanics, the test aids in early detection and proper management of arch-related foot disorders.

Most Useful Resources:
Jacks Test (Podiapaedia)
Jacks Test and failure of STJ supination with ext tibia rotation (Podiatry Arena)
Is Jacks test valid? (Podiatry Arena)
The Hubscher maneuver or Jacks test? (Podiatry Ninja)
Jacks Test (Bunion Surgery)

Foot Posture Index

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Foot Posture Index is a composite measure of the posture of the foot based on 6 different observations of the alignment or posture of different segments of the foot.

The Foot Posture Index (FPI) is a widely used clinical tool for quantifying standing foot posture, helping to classify feet as pronated, neutral, or supinated. The most common version is the FPI-6, which involves observing and scoring six specific criteria. This assessment is quick, simple, and reliable, making it valuable for clinicians and researchers alike.

Here’s how to calculate the FPI-6:

1. Preparation and Patient Positioning
The patient should stand barefoot in a relaxed, neutral stance with both feet supporting their weight. Their arms should be naturally at their sides, and they should look straight ahead. It can be helpful to have them march in place for a few steps before settling into their stance. The assessment usually takes about two minutes, and the assessor needs to be able to move around the patient freely.

2. The Six Criteria and Scoring
Each of the six criteria is scored on a 5-point scale, ranging from -2 to +2. A score of 0 indicates a neutral position for that specific criterion. Positive values (+1, +2) are given for pronated features, with higher scores indicating more pronation. Negative values (-1, -2) are given for supinated features, with more negative scores indicating more supination. If an observation cannot be made (e.g., due to swelling), it should be skipped and noted.

The six criteria are:

  • Talar Head Palpation (Transverse Plane): This involves palpating the talar head. The score depends on whether the talar head is more palpable on the lateral (outer) or medial (inner) side of the foot.
  • Curves Above and Below the Lateral Malleolus (Frontal/Transverse Plane): Observe the curvature around the ankle bone (lateral malleolus) from behind. The score is based on whether the curve below the malleolus is straight, convex, or more or less concave compared to the curve above it.
  • Calcaneal Frontal Plane Position (Frontal Plane): Observe the heel bone (calcaneus) from behind. The score reflects whether the heel is inverted (varus), everted (valgus), or vertical, often estimated in degrees.
  • Prominence in the Region of the Talonavicular Joint (Transverse Plane): View the inside of the foot at an angle. The score depends on whether this area is concave, flat, or bulging.
  • Congruence of the Medial Longitudinal Arch (Sagittal Plane): Observe the inner arch of the foot from the inside. The score ranges from a high, acutely angled arch to a very low, flattened arch that might be making ground contact.
  • Abduction/Adduction of the Forefoot on the Rearfoot (Transverse Plane): View the foot from behind. The score is based on how many medial (inner) or lateral (outer) toes are visible, indicating whether the forefoot is abducted (splayed out) or adducted (turned in) relative to the rearfoot.

3. Total Score and Classification
After scoring each of the six items, sum the individual scores to get a total FPI-6 score. The total score can range from -12 (severely supinated) to +12 (severely pronated). The foot posture is then classified based on this total score:

  • Severely Supinated: ≤ -5
  • Mildly Supinated: -1 to -4
  • Neutral Posture: 0 to +5
  • Mildly Pronated: +6 to +9
  • Severely Pronated: ≥ +10

It’s important to note that a slightly pronated foot posture (mean raw score of +4) is considered the normal position at rest in a healthy adult population. The FPI is a practical tool that aids in deciding appropriate interventions, such as strengthening exercises, stretching, manual therapy, gait training, or selecting suitable orthotics.

Most Useful Resources:
Foot Posture Index (Podiatry TV)
The Foot Posture Index (Podiatry Update)
Foot Posture Index (Clinical Boot Camp)
Foot Posture Index (PodiaPaedia)
Foot Posture Index (Podiatry Arena)

Forefoot Supinatus

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Forefoot supinatus is a common foot type in which the forefoot is inverted relative to the rearfoot. In comparison o a bony foefoot varus, the supinatus is a soft tissue contracture.

Forefoot supinatus is a positional deformity of the forefoot, commonly seen in patients with flatfoot (pes planus) or other structural imbalances. It refers specifically to the inversion (upward and inward tilt) of the forefoot relative to the rearfoot, not due to a bony abnormality but rather due to soft tissue adaptation. It’s often a flexible deformity, meaning that the bones are not fixed in this position and the forefoot can be manually corrected to a neutral or pronated position. This makes it different from rigid forefoot varus, which is a structural and non-reducible condition.

The key thing with forefoot supinatus is that it’s usually a compensatory mechanism. When someone has excessive rearfoot pronation—basically, their heel rolls inward too much during walking—the forefoot can adapt by inverting to try and keep the medial column (the inner part of the foot) in contact with the ground. Over time, soft tissues on the lateral (outer) side of the forefoot can tighten, leading to a maintained supinated position even when the person is non-weight bearing. This is often assessed clinically by checking the flexibility of the forefoot in a non-weight-bearing position.

Diagnosing forefoot supinatus involves a combination of physical examination and sometimes gait analysis. A podiatrist or orthopedist might look at the subtalar joint, assess rearfoot and forefoot alignment, and determine whether the forefoot can be corrected manually to a neutral or pronated position. A positive “Hubscher maneuver” (also known as the Jack test) can indicate flexibility in the arch, which may help distinguish supinatus from more rigid deformities. It’s also important to differentiate it from forefoot varus, as the treatment approach differs significantly.

Treatment for forefoot supinatus focuses on addressing the root cause, typically the excessive rearfoot pronation. Custom foot orthoses with medial arch support and possibly forefoot posting can help realign the foot and offload stress from compensatory structures. In some cases, stretching and strengthening exercises are prescribed to restore muscular balance and improve flexibility. Since the condition is positional and soft-tissue based, early intervention can often correct or significantly improve the deformity without the need for surgery.

Most Useful Resources:
Forefoot Supinatus (PodiaPaedia)
Help needed with forefoot supinatus? (Podiatry Arena)
The effect of forefoot varus on the hip and knee and the effect of the hip and knee on forefoot supinatus … (Running Research Junkie)

The Determinants of Gait

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The Determinants of Gait are the biomechanical strategies that the body uses in order to maintain the center of gravity in the horizontal plane, as well as increase efficiency and to decrease the expenditure of energy when walking and running

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The Determinants of Gait are a set of six distinct movements that occur during the gait cycle to minimize the vertical and horizontal displacement of the body’s center of gravity. The primary purpose of these movements is to make walking more energy-efficient and smooth. Without these determinants, a person’s walk would be an inefficient “compass gait,” characterized by a significant up-and-down motion. The selected text from the Canvas document describes the general gait cycle, but doesn’t go into these specific, energy-saving movements.

 

The six classic determinants of gait are:

  • Pelvic Rotation: The pelvis rotates forward on the side of the swinging leg. This action lengthens the stride and reduces the peak of the body’s center of gravity, smoothing out the vertical path.
  • Pelvic Tilt (or Pelvic Obliquity): During the swing phase, the pelvis on the non-weight-bearing side drops slightly. This also helps to lower the body’s center of gravity, preventing an excessive rise as the body moves over the stance leg.
  • Knee Flexion in Stance Phase: As the foot makes contact with the ground, the knee flexes slightly. This acts as a shock absorber and prevents the body’s center of gravity from rising too high during the middle of the stance phase.
  • Foot and Ankle Mechanisms: This refers to the coordinated movements of the ankle and foot. The plantarflexion of the foot at heel strike and the subsequent dorsiflexion work to smooth the path of the body’s center of gravity.
  • Knee and Ankle Interaction: The way the knee and ankle move together also contributes to maintaining a smooth center of gravity. The knee begins to flex after heel strike and extends later in the stance phase, while the ankle’s rotation also changes the effective length of the leg, keeping the body’s center of gravity from oscillating too much.
  • Lateral Pelvic Displacement: The body shifts from side to side over the stance leg to keep the center of gravity over the base of support. This reduces the lateral, or side-to-side, displacement of the center of gravity.

Together, these six determinants work to create the smooth, undulating path of the body’s center of gravity, which is essential for an efficient and effortless walk.

Most Useful Resources:
Determinants of gait (Foot Health Forum)
Determinants of gait discredited? (Podiatry Arena)
The Determinants of gait (Podiatry Arena)
Determinants of Gait (PodiaPaedia)
Determinants of Gait (Podiatry TV)
The Six Determinants of Gait (Podiatry Ninja)

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Cluffy Wedge

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The Cluffy wedge is a pad that is places under the great toe to hold it in a slightly dorsiflexed position. It is designed to treat functional hallux limitus and problems with the windlass mechanism.

The Cluffy Wedge is a trademarked pad designed to sit under the hallux (your big toe), aiming to hold it in a gently dorsiflexed position—that is, lifted upward just enough to get things moving right. Originally developed by Dr. James Clough, DPM, this wedge was first trademarked in 2003 under Cluffy LLC in Polson, Montana, and has also been marketed under the name P4 Wedge.

Functionally, the Cluffy Wedge is all about managing a condition called functional hallux limitus—where your big toe has a normal range of motion when off the ground but gets stuck when you’re weight-bearing. By dorsiflexing the hallux, the wedge preloads the toe so the windlass mechanism (which tightens the plantar fascia during walking) kicks in earlier and more naturally . The theory is sound: first metatarsal loading improves, less strain is placed on the other metatarsals, and the foot’s biomechanics get realigned—at least hypothetically.

On the practical side, you can use the Cluffy Wedge on its own inside shoes, under insoles, or as an extension in custom orthotics. While some podiatric labs initially offered it, most now craft their own versions to achieve the same effect—often by adding padding under the hallux in custom orthotic designs. However, it’s important to note that peer-reviewed clinical trials are lacking, so much of what we have are anecdotal reports, small-scale studies, or theses—not yet full clinical validation.

In short, the Cluffy Wedge stands out as a simple yet biomechanically savvy tool for specific foot dysfunctions, especially functional hallux limitus. While its theoretical benefits—like balancing forefoot pressure and reactivating the windlass mechanism—are appealing, we remain a bit short on robust clinical research. Still, for patients and practitioners looking for non-invasive ways to support hallux mechanics, it’s worth considering, especially if integrated thoughtfully into custom orthotic planning.

Most Useful Resources:
Cluffy Wedge (Foot Health Forum)
Cluffy Wedge (Podiatry Arena)
Cluffy Wedge (Clinical Biomechanics Bootcamp)
Cluffy Wedge (PodiaPaedia)
The Cluffy Wedge (Podiatry Update)
Cluffy Wedge (Podiatry Experts)

Overpronation

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‘Overpronation’ is generally accepted as being the foot rolling inwards at the ankle or rearfoot joints. There is a lot of controversy about the use of the term; just how much of a risk factor for injury it is; if it should be treated or not; and what the best treatment for it should be.

overpronation

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Overpronation in runners refers to an excessive inward rolling of the foot after it strikes the ground during running. While some degree of pronation is natural and helps absorb shock, overpronation places extra stress on the foot and leg. When the foot rolls too far inward, it disrupts proper alignment and alters how forces are distributed across the lower body. This can affect not only the feet but also the ankles, knees, hips, and even the lower back, making it a common biomechanical issue among runners.

One of the main causes of overpronation is structural or biomechanical imbalances. Flat feet, low arches, and ligament laxity often predispose runners to roll their feet inward. Other contributing factors include weak stabilizing muscles in the hips and legs, improper running technique, or wearing shoes without sufficient support. Over time, these factors can combine to exaggerate the inward collapse of the foot, leading to poor shock absorption and inefficient running mechanics.

The symptoms and risks of overpronation are varied. Runners often experience pain in the arch or heel, shin splints, plantar fasciitis, Achilles tendonitis, and knee discomfort due to the misalignment of the leg. Overpronation may also contribute to overuse injuries, since the body compensates for poor foot mechanics with increased stress on surrounding joints and muscles. Recognizing these symptoms early can help runners avoid more serious chronic injuries that could interrupt training.

Management and prevention strategies typically involve strengthening exercises, supportive footwear, and sometimes orthotics. Strengthening the intrinsic foot muscles, calves, and hip stabilizers can improve foot control and alignment. Choosing stability or motion-control running shoes with proper arch support can reduce excessive pronation. For runners with more severe cases, custom orthotics may be prescribed to correct biomechanics. Additionally, focusing on proper running form and gradually increasing training load can reduce the likelihood of injury from overpronation. This balanced approach allows runners to maintain performance while protecting long-term joint health.

Most Useful Resources:
Overpronation (Foot Health Forum)
Overpronation in Runners (Podiatry Update)
Overpronation (Podiatry Online TV)
How do you treat overpronation? (Podiatry Experts)
My Advice if you Overpronate (Running Injury Advice)
Overpronation (Dr the Foot Without the Dr)
‘Overpronation’ (Podiatry CPD)
Pronation Mythology (Its a foot, Captain)
The nonsensical understanding of ‘overpronation’ (Run Research Junkie)
Is Overpronation a Problem? (Clinical Boot Camp)
“Biomechanics Corner”: Overpronation (Podiatry Arena)
Overpronation (Foot Info)
Overpronation (Podiatry Daily)

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The Abductory Twist During Gait

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An abductory twist is a reasonable common observation during a gait analysis and is caused by a number of different things. It is commonly associated with ‘overpronation‘. It is seen as a sudden abduction or whip of the heel medially (abduction) just as the heel comes off the ground. See this video for what it looks like:

The abductory twist is a subtle motion observed during the gait cycle, specifically in the propulsion phase of walking. It occurs when the heel lifts off the ground, and just before the toes push off, the heel shows a slight medial rotation (inward turn). This twist is often not dramatic—typically visible as a quick, small flick at the heel—but it can be a key indicator of underlying biomechanical inefficiencies or pathology in foot mechanics. It reflects a delay or compensation in the foot’s ability to resupinate (return to a supinated or rigid state) in preparation for toe-off.

From a biomechanical perspective, the abductory twist is closely tied to the function of the subtalar joint and midfoot stability. In a typical gait, the foot pronates (flattens) after heel strike to absorb shock, then transitions into supination as the body moves forward to create a rigid lever for propulsion. When this resupination is delayed or incomplete—due to issues like overpronation, forefoot varus, or tight calf muscles—the rearfoot compensates with a twisting motion to allow toe-off. This can cause excess stress on the plantar fascia, medial knee structures, or even contribute to hip and lower back pain if not addressed.

Clinically, the abductory twist is often associated with conditions like posterior tibial tendon dysfunction, flatfoot deformity, or excessive pronation syndromes. Identifying this motion during gait analysis helps clinicians determine the need for orthotic intervention, strengthening of intrinsic foot muscles, or stretching regimens. In children, a persistent abductory twist may suggest developmental alignment issues. Ultimately, while it might seem like a minor detail, the abductory twist provides valuable insights into kinetic chain dysfunction and should not be overlooked in comprehensive gait assessment.

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Most Useful Resources:
Biomechanics of abductory twist (Foot Health Forum)
The abductory twist (Podiatry Update)
The doc said I have an abductory twist… ? (Podiatry Experts)
My advice if you have an abductory twist (Running Injury Advice)
The Medial Heel Whip (Physio Ninja)
An Abductory Twist (Dr the Foot Without the Dr)
Abductory Twist: Throw the kitchen sink at it (Kitchen Sink)
Understanding the Abductory Twist (AgonyDeFeet)



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Muscle Strength and Arch Height

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There is apparently a lot of controversy on the roles of muscles and muscle strength on the height of the arch in the foot. Almost all of the research shows that there is no relationship between muscle strength and arch height; no relationship between overpronation and muscle strength; and the evidence also shows that foot orthotics do not weaken the muscles neither. There is really no controversy, the evidence is clear.

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Most Useful Resources:
Foot Arches and Muscle Strength (PodiaPaedia)
Overpronation and Muscle Strength (PodiaPaedia)
Foot Orthotics and Muscle Strength (PodiaPaedia)
Increase in muscle strength with foot orthotic use (Podiatry Arena)
Do foot orthoses weaken “arch” muscles? (Podiatry Arena)
Do Foot Orthoses Weaken Feet/Legs? (Podiatry Arena)

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