Everything you need to know about shoes

Running Shoes: Four Flimsy Paradigms and What We Actually Know

Let's talk about running shoes and the complete cluster of conflicting evidence around them. If you've ever stared at the wall of technicolor foot-coffins at your local running store and thought "what the hell is the difference between all these?" – you're in good company. Your patients are wondering the same thing, and they expect you to have answers because you've got those fancy letters after your name. Too bad the evidence is about as solid as a minimalist shoe in a mud puddle.

This article dives deep into the murky waters of running shoe science, examining the four major paradigms that have driven shoe design and recommendations over the past half-century. And I’ve broken it down for you here. Spoiler alert: none of them have rock-solid evidence, and your safest bet is to recommend lightweight, comfortable shoes with minimal pronation control. But let's not get ahead of ourselves – there's a whole buffet of science to digest first.

The Basics: What's Actually in a Running Shoe?

Before we wade into the paradigms, let's break down what we're dealing with. Running shoes have two major components:

1. The upper: Covers the dorsum and heel of the foot, including the lacing system and heel counter. It influences breathability and fit, but surprisingly little research exists on how these components affect injury or performance. It's like the research community has collectively decided, "Nah, the top part couldn't possibly matter."

2. The sole: This is where all the magic (or snake oil) happens, consisting of:

   • Insole: That (usually) removable foam footbed that your patients probably replace with something else anyway

   • Midsole: The meaty part with all the proprietary technology and fancy marketing names

   • Outsole: The rubber that contacts the ground and wears out way faster than anyone would like

The midsole is where shoe companies pour their R&D dollars and marketing budgets. It can be described by:

• Thickness (stack height) – from paper-thin to moon boots

• Heel-to-toe drop – from zero to "basically high heels"

• Motion control/stability features – those colorful medial wedges that may or may not do anything useful

• Flexibility (bending stiffness) – from wet noodle to carbon-plated supershoes

• Material composition - foams, carbon plates, air bags, gel pockets, and whatever other gizmos they can cram in there

Now let's dive into the four major paradigms that have driven shoe recommendations over the years, starting with everyone's favorite biomechanical bogeyman.

Paradigm 1: Pronation Control

The Rationale: Excessive pronation at the subtalar joint during stance increases stress on the anterior medial region of the knee, leading to pain/injury. Since pronation promotes internal rotation of the tibia through joint coupling with the foot, which in turn was thought to place greater stress at the tibiofemoral and/or patellofemoral joints. Since most recreational runner injuries occur at the knee, controlling pronation seemed like a logical intervention to reduce knee pain and injury.

Key Footwear Feature: "Motion control" technology – that dense, usually darker colored midsole material along the mediolateral arch to reduce midfoot pronation during stance. Alternatively, or additionally, posting or wedging at the rear portion of the shoe to reduce rearfoot motion and provide increased stability to the heel. These features often add significant weight to the shoe, which is a separate issue we'll get to later.

Assessment Method: Evaluate static foot posture in standing (arch height, navicular height, rearfoot eversion from subtalar neutral) or use the Foot Posture Index (FPI-6). Some clinicians watch runners perform single leg squats to observe changes in arch/navicular height combined with knee frontal plane position. If space permits, they might ask runners to actually run (revolutionary concept) while examining rearfoot eversion and pronation at midstance, either qualitatively or using 2D video analysis.

The Recommendation Formula:

• "Low" arch + "very excessive" pronation = motion control shoe (heavy, stiff, and expensive)

• "Medium" arch + "excessive" pronation = stability shoe (slightly less heavy, less stiff, and equally expensive)

• "High" arch + "normal" pronation = neutral shoe (might actually be pleasant to run in)

Important note: There's no standard threshold for what counts as "excessive" pronation. Normative running biomechanics suggest the rearfoot is typically in 6°-8° of calcaneal inversion at initial contact and shifts to ~6°-8° of eversion by midstance. Beyond that, it's largely based on the clinician's vibes and how dramatic they want to be when telling you your feet are "collapsing."

The Evidence: Multiple studies confirm that motion control technology can effectively alter rearfoot motion. So at least that part works. But does it matter? Large prospective studies on military recruits found that assigning shoes based on arch type did not significantly reduce the rate of injuries during 12 weeks of basic training. One study even found that female recreational runners randomly assigned to motion control shoes incurred more missed days (79 days) due to pain during a 13-week half marathon training program than those assigned neutral (64 days) or stability (51 days) shoes.

The underlying assumption that excessive pronation causes injury has also been challenged, with studies showing it's not a risk factor for non-specific injuries in novice runners and wasn't associated with specific types of running-related injuries. Moreover, limited evidence exists to indicate that structural alignment is a primary risk factor for injury or that static foot posture accurately reflects dynamic foot motion during running.

So the evidence suggests that 1) we can change pronation with shoes, 2) it probably doesn't reduce injuries, and 3) might actually cause more problems. Great start!

TL;DR: This paradigm assumes excessive pronation causes injuries and uses motion control features to reduce it. Evidence shows these features do alter foot motion but don't reduce injuries and might actually cause more problems.

Paradigm 2: Impact Force Modification

The Rationale: Excessive forces imparted on the body during the impact phase of running contribute to injury. Specifically, the impact peak and loading rate (slope of the rising portion) of the vertical ground reaction force were targeted. A larger (steeper) vertical ground reaction force loading rate has been suggested as a risk factor for injury in distance runners, though recent prospective studies call this into question.

The presence of an impact peak is typically associated with rearfoot striking, whereas it's less pronounced or absent in non-rearfoot striking. This distinction becomes important for understanding minimalist shoes (promoting non-rearfoot striking to reduce impact) versus maximalist shoes (using cushioning to absorb impact forces).

Key Footwear Feature: Midsole cushioning, historically through materials that absorbed more energy at impact. Since the mid-2000s, variations in midsole thickness have also been employed, allowing for different heel-to-toe drops and integration of additional technology like carbon fiber plates.

Assessment Method: Traditionally required expensive laboratory-based force platforms or instrumented treadmills, which aren't exactly practical in clinical settings. More recently, wearable accelerometers have been used to measure peak positive tibial acceleration as a surrogate for loading rate, while force-sensing insoles can directly measure vertical ground reaction force during running.

In practice, clinicians often rely on observing kinematic correlates: foot strike pattern, foot inclination angle, step rate, and stride length. Runners who rearfoot strike tend to have lower step rates, longer strides, and higher magnitudes of peak vertical ground reaction force and loading rates than non-rearfoot strikers. Following the paradigm, clinicians would recommend more cushioned shoes to these runners to mitigate these forces.

The Evidence: Current research doesn't support that increasing cushioning via midsole material reduces external vertical ground reaction forces. Studies using in-sole pressure sensors have found differences in impact across cushioning levels, but the effect on actual injury risk remains unclear. Two studies examining cushioning and injury risk showed mixed results, with only lighter runners experiencing a protective effect from cushioning.

This paradigm spawned two opposing shoe movements:

1. Minimalist Shoes (mid-2000s): Fueled by barefoot running enthusiasm, these thin, flexible shoes with minimal technology were designed to permit free motion of the foot, achieving a more barefoot-like running style. The rationale was that barefoot running promotes a forefoot strike pattern that eliminates the impact peak on the vertical ground reaction force curve. The Reality Check: Not all runners switch to a forefoot strike in minimalist shoes, and those who maintain a rearfoot strike actually show higher impact forces than in conventional shoes. Studies found higher vertical ground reaction force loading rates and impact peaks when running in minimalist compared to conventional shoes. Switching from traditional to minimalist shoes may contribute to short-term (up to 12 weeks) foot and lower leg pain or injury but could produce plantar-flexor strength gains longer-term (20 weeks). Body mass also matters – heavier runners seem to be at greater risk of injury in minimalist shoes.

2. Maximalist Shoes (more recent): On the opposite end of the spectrum, shoes with more than 20mm midsole thickness and minimal support technology. While they don't seem to reduce vertical ground reaction force or joint forces, they appear less likely to cause running-related pain or time loss compared to minimalist shoes, suggesting there may be some protective value in thick midsoles.

TL;DR: Aimed to reduce impact forces through cushioning. Led to both minimalist shoes (promoting forefoot striking) and maximalist shoes (thick cushioning). Research doesn't clearly support that cushioning reduces impact forces or injuries.

Paradigm 3: Habitual Joint (Motion) Path

The Rationale: Each runner has a unique trajectory for joint motion. The magnitude may fluctuate, but the trajectory or path remains stable. Footwear that resists this natural path may increase tissue stress, either from forcing a deviation or from increased muscle activity trying to maintain the preferred path. Originally called the "Preferred Movement Path," this was later renamed the "Habitual Joint Motion Path," adding that joint motion takes the path of least resistance due to individual anatomy and passive tissue properties.

Research using bone pins in the femur, tibia, and calcaneus found minimal variation in skeletal movement despite changes in footwear, supporting the concept that runners have an individual joint motion path.

Key Footwear Feature: Since habitual joint motion patterns are subject-specific, there's no specific key feature. An example might be minimal arch support that allows the preferred movement of pronation rather than a medial post forcing a more supinated position.

Assessment Method: No standardized clinical tests exist to assess variability or deviation from the habitual path. Researchers have developed field methods comparing lower-limb kinematics during double-legged half squats (as baseline) versus running in a "sock shoe" (minimal cushioning but no support technology). Knee and ankle kinematics are compared to determine if the runner is a "high deviator" or "low deviator," with shoes deemed appropriate if they decrease the difference between running and half-squat kinematics.

The Evidence: Few studies have investigated this paradigm by examining how footwear influences movement variability. Some researchers define "footwear-related variability" as how much a runner's movement patterns change across different shoes. Runners with high variability may be more sensitive to footwear, less able to maintain their habitual motion path, and potentially at higher risk of injury.

One study found that increased time outside one's habitual motion path was associated with cartilage volume reductions in the knee joint after 75 minutes of running. However, no studies have directly tested whether matching footwear to minimize deviation from the habitual path actually reduces injury rates. So while the concept is interesting, the practical application remains theoretical.

TL;DR: Proposes each runner has a unique joint motion path that shouldn't be disrupted. Interesting concept but lacks practical assessment methods and evidence that matching footwear to maintain this path reduces injuries.

Paradigm 4: Comfort Filter

The Rationale: A runner intuitively selects shoes that are biomechanically optimal based on comfort. This paradigm suggests subjective comfort is the most important factor for selecting running footwear to reduce injury risk. The hypothesis is that increased impact forces lead to more soft tissue vibrations, which must be counteracted by muscle activation ("muscle tuning"). This feels uncomfortable and requires higher energy expenditure.

The concept emerged partly from research on military personnel, where soldiers who received their most comfortable insole had 53% fewer lower-extremity injuries than a control group without insoles during 4 months of training. Interestingly, five out of six insole types were selected as "most comfortable" at similar rates, suggesting comfort is linked to individual-specific rather than insole-specific factors.

Key Footwear Feature: No specific feature, since comfort is subjective and runner-specific, but likely influenced by midsole thickness, cushioning, resiliency, and overall fit.

Assessment Method: There are validated methods to accurately assess shoe comfort in research settings, but practically, there's no standardized clinical method other than asking the runner which feels best. Revolutionary, I know.

The Evidence: Limited research has explored the connection between comfort and biomechanical variability. One study examining coordination variability of lower extremity joint pairings in relation to most and least comfortable shoes found no evidence supporting this connection. Besides the military insole study, no other research has conclusively linked comfort and injury reduction.

TL;DR: Suggests runners intuitively select shoes that are biomechanically optimal based on comfort. Limited evidence connects comfort to reduced injury risk, despite its intuitive appeal.

Performance Considerations: Beyond Injury Prevention

While most paradigms focus on injury reduction, performance matters too, especially for competitive runners. Here, the evidence is somewhat clearer:

Mass: The feature with the clearest link to performance is weight. Every 100g (3.5oz) added to a shoe increases oxygen consumption by ~1% and running time per distance. This is why elite marathon racers were wearing what amounted to glorified slippers until the recent supershoe revolution.

Longitudinal Bending Stiffness: Often influenced by carbon fiber plates, increased stiffness has been found to reduce negative work at the metatarsophalangeal joint and alter the ground reaction force moment arm in ways that may reduce oxygen consumption. However, when researchers removed the carbon plate from the Nike Vaporfly, they found no change in oxygen consumption rate, challenging the assumed mechanism.

Some researchers suggest it's the curved shape rather than stiffness that drives performance gains through a "teeter-totter effect," creating a larger upward force on the heel that helps propulsion. The optimal amount of stiffness and curvature seems to be runner- and task-specific, but no method exists for customizing these features to individual runners.

Midsole Thickness: Affects performance through multiple mechanisms:

• Too little increases metabolic cost by requiring higher muscle activity to absorb impact

• Shod running shows 3-4% lower oxygen consumption than barefoot running

• Increasing thickness increases effective leg length, potentially improving performance

• Too much thickness unnecessarily increases mass and may require more muscle activity to control frontal and transverse plane movement if the stack height creates instability

Midsole Resiliency: The relationship between thickness and material properties that lead to energy return isn't well-established. Some studies found improvements in running economy with resilient midsole materials, while others saw no difference compared to conventional EVA foam. The Nike Vaporfly's performance gains seem partly due to its highly resilient thick midsole made from innovative materials that keep added mass low.

Comfort and Performance: One study found a small (0.7%) improvement in running economy in the most (vs. least) comfortable shoe, but a more recent study found no significant difference in oxygen consumption between the most and least comfortable options.

TL;DR: Shoe weight most clearly affects performance (lighter is better). Other factors like bending stiffness, midsole thickness and resiliency can improve running economy, but optimal features vary by individual.

Real-World Applications: What We Tell Our Patients

Based on current evidence, the scientifically supported general recommendation is:

Pick the lightest and most comfortable shoe with the least amount of pronation control technology.

But this one-size-fits-all approach is likely insufficient. Context matters tremendously:

1. Runner Characteristics: Consider their biomechanics, strength, stability, injury history, and anthropometrics (especially body mass).

2. Running Purpose: Different shoes may be appropriate for long runs, speed work, races, or trail running.

3. Specific Biomechanical and Tissue Responses: Here are some examples the authors provide:

   • Thicker Midsoles: May provide more cushioning and comfort but could challenge ankle stability. Runners who typically rearfoot strike but lack ankle stability might risk sprains or peroneal tendonitis. Increased stack height may also lead to longer strides and lower step rates, increasing loads on the hip and surrounding musculature – potentially problematic for runners with poor hip strength or existing hip pain.

   • Minimalist Shoes: May increase strain on posterior chain musculature either directly through reduced heel-to-toe drop or indirectly by increasing step rate. These might be inappropriate for runners with acute posterior muscle strains or tendonitis but could help improve tendon stiffness and strength in chronic conditions if properly dosed.

   • New Foam Materials: Shoes like the Nike Vaporfly influence mechanical work and power at the ankle. Runners with acute Achilles tendonitis might benefit short-term from reduced ankle work, but consistent long-term use might degrade Achilles tendon stiffness, potentially creating problems for multi-sport or multi-event athletes. Runners susceptible to Achilles issues might benefit from reserving these shoes for racing while training in different models to maintain tendon stiffness.

The authors suggest that diversifying footwear based on run type and runner characteristics might optimize outcomes, though more research is needed. One study found that runners who rotated between multiple shoe models had a 39% lower risk of running-related injury than those using a single pair, but other evidence is mixed.

The Bottom Line: Your Clinical Takeaways

After decades of research and marketing hype around running shoes, the evidence supporting any of these paradigms is remarkably thin. This doesn't mean shoes don't matter – they clearly influence biomechanics – but the connections between specific shoe features, biomechanical changes, and injury prevention or performance enhancement remain murky at best.

As clinicians, we need to understand the basics of shoe construction, be aware of these paradigms, and recognize that the best approach is likely individualized recommendations based on runner characteristics, goals, and comfort preferences rather than rigid adherence to any single paradigm. We should arm ourselves with understanding how specific footwear features affect biomechanics to make better patient-specific recommendations.

The most important lesson? Stop telling everyone they overpronate. It's probably not causing their problems, and the motion control shoes you're recommending might actually be making things worse. Science is cool like that – constantly proving us wrong and forcing us to update our thinking, even if the running shoe industry (and many clinicians) haven't gotten the memo.

And if a patient asks you which specific shoe they should buy? Unless you've thoroughly assessed them, their goals, and their injury history, the most evidence-based answer might just be: "The one that feels the best on your foot that doesn't have a bunch of anti-pronation technology... and maybe buy a couple different pairs to rotate between." Not exactly the sage wisdom they were hoping for from their PT, but at least it's honest.

TL;DR: Evidence for any shoe paradigm is thin. Make individualized recommendations based on runner characteristics, goals, and comfort rather than rigidly following any single paradigm. Stop over-diagnosing pronation issues.