Choosing Running Shoes Correctly: Scientific Criteria for Fit and Foot Health

What lies behind it

To understand the necessity of selecting anatomically correct footwear, the biomechanics of the foot during running must be examined. Upon ground impact, a multiple of body weight acts upon the structures of the foot. To absorb these forces, the human foot possesses a natural cushioning mechanism, which relies primarily on the flexibility of the longitudinal and transverse arches.

Under this dynamic load, the arch flattens. The foot expands in length by several millimetres and becomes significantly wider in the forefoot area. This phenomenon is termed functional foot expansion. If the foot is constricted by overly narrow shoe construction at this moment, it cannot perform its natural shock-absorbing function. Pressure is not distributed evenly, concentrating instead on small areas of tissue.

Last width plays a central role in this process. The last is the three-dimensional mould upon which a shoe is constructed. Every manufacturer uses distinct last shapes, which vary considerably in forefoot width, heel width, and instep height. If the width of the last does not match the morphology of the foot, the forefoot becomes compressed. The metatarsals are squeezed together, narrowing the space for the nerves and blood vessels running between them.

The design of the toe box is equally critical. The human hallux (great toe) plays a fundamental role in stability and propulsion. It should ideally align directly with the first metatarsal bone. However, many modern running shoes taper symmetrically towards the tip. This forces the hallux outwards while crowding the smaller toes inwards. This artificial narrowing impairs the windlass mechanism, in which the tensioning of the plantar fascia over the metatarsophalangeal joint of the hallux stabilises the longitudinal arch.

Typical signs

Incorrectly selected running shoes leave clear signs on the skin, nails, and musculoskeletal system. One of the most common indicators of inadequate length or an overly shallow toe box is a subungual haematoma, commonly known as a black or bruised toenail. With every step, the apex of the toe strikes the upper material of the shoe. Repeated microtrauma leads to bleeding beneath the nail plate. In the longer term, this can result in onycholysis, the detachment of the nail plate from the nail bed, or permanent nail growth disorders such as onychauxis (thickening of the nail).

At the pressure points of the balls of the feet and the toe joints, the skin responds with increased keratinisation. These hyperkeratoses represent a biomechanical protective mechanism against excessive friction and shear stress. If pressure remains locally confined, painful corns (clavi) can form, extending deep into the tissue.

Another typical symptom is the onset of numbness, tingling, or burning pain in the area of the middle toes during or after running. These complaints indicate compression of the plantar nerves. Pressure from an overly narrow forefoot section pinches the nerves between the metatarsal heads. If this irritation persists over prolonged periods, a structural thickening of the nerve, known as a Morton's neuroma, can develop.

Pain in the plantar surface of the foot or the Achilles tendon can also stem from ill-fitting footwear. Inadequate heel guidance or an abrupt change in heel-to-toe drop (the height difference between heel and forefoot) overburdens the insertion points of the tendons and the plantar fascia.

Everyday causes

Clinical practice reveals recurring patterns of causes leading to unsuitable purchases and subsequent foot problems. Primary among these is relying on static shoe size. Many runners purchase running shoes in the same size as their street shoes. However, because the foot expands under load and slides forward when running downhill, street shoe size is almost invariably too small for running footwear.

Another issue is the influence of fashion trends and aesthetic design. Narrowly cut shoes appear sporty and dynamic, yet contradict the anatomical reality of many feet. Uncritical reliance on categories such as neutral shoe or stability shoe also frequently leads to misguided choices. A shoe featuring pronounced pronation support can cause overcorrection in individuals without alignment deficits, resulting in ankle and knee pain.

Material degradation is another regularly underestimated factor. Cushioning materials, typically ethylene-vinyl acetate (EVA) or polyurethane (TPU), lose their corrective and shock-absorbing properties through mechanical strain and plasticiser breakdown. A running shoe may appear visually pristine, yet be biomechanically worn out after 600 to 800 kilometres of running. The cushioning collapses unevenly, intensifying abnormal mechanical loads.

Consistently wearing the exact same shoe model for all training sessions also deprives the intrinsic foot muscles of varied stimuli. The foot adapts monotonously to the geometry of that single shoe. A lack of variation weakens the intrinsic muscular self-stabilisation of the foot.

When medical evaluation is necessary

Not all foot complaints can be resolved solely through podiatric treatment or changing footwear. Clear warning signs exist that necessitate further orthopaedic, neurological, or vascular diagnostic evaluation.

Persistent, sharp pain in the midfoot or heel area that does not subside during rest periods or alters gait mechanics requires investigation. This could indicate a stress fracture of a metatarsal bone or severe inflammation of the plantar fascia (plantar fasciitis).

Sudden, severe swelling, erythema, or localized heat in the toe joints or ankle joint also demand prompt medical assessment. If sensory disturbances such as numbness or paresthesia occur not only during running but persist continuously, a neurological underlying cause must be ruled out.

Individuals with established underlying conditions such as diabetes mellitus or peripheral arterial disease must never self-treat or ignore pressure points or injuries. With reduced pain perception, unmanaged pressure sores can rapidly progress to deep ulcers. In such cases, close coordination with attending medical specialists is imperative.

What podiatric treatment can achieve

Medical podiatry intervenes where shoe-related pressure points and nail changes have already caused tissue damage. Treatment begins in the practice with a thorough medical history and visual assessment of the foot. Keratinisation patterns, nail deformities, and structural misalignments are analysed. In addition, the structure of affected skin areas can be evaluated within the specialist practice to initiate targeted interventions. Detailed information regarding our procedures can be found under /en/services.

For inflamed or painful nail folds caused by pressure from an overly tight toe box, professional management of the nail margins is performed. Ingrown or high-pressure nail segments are gently removed. Should the nail have become deformed through chronic pressure, nail brace therapy (orthonyxia) can be applied. This encourages flat re-growth of the nail plate and permanently relieves pressure on the sensitive nail bed.

Excessive callus and corns are precisely and bloodlessly debrided using rotary diamond burs and scalpel techniques. To prevent recurring pressure peaks, podiatrists craft custom-moulded silicone orthoses. These custom devices fit precisely between the toes, effectively absorbing shear stress inside the running shoe.

Depending on the extent of tissue alterations, podiatric treatment requires regular intervals. Intervals of four to six weeks are typically recommended to medically monitor and manage the regrowth of nails and hyperkeratosis. Practice proprietor Helga Maria Freitag cares for patients with her dual qualification as a state-recognised podiatrist and sectoral practitioner for podiatry (sektorale Heilpraktikerin für Podologie).

What you can do yourself

When purchasing running shoes, a systematic approach can prevent the majority of common errors. Selection should not be guided by colour or brand popularity, but by clear biomechanical requirements.

A proven tool for initial self-assessment is the insole test. Remove the factory-supplied insole from the shoe and stand barefoot upon it under full weight bearing. The foot must not project beyond the margin of the insole at any point. A clearance of approximately 12 to 15 millimetres should remain in front of the longest toe, which is by no means always the hallux, but in many individuals the second toe. If the insole is too narrow along the sides, the shoe will likewise compress the forefoot during the running stride.

Equally important is considering the intended area of use and running shoe rotation. Alternating between multiple pairs of running shoes offers scientifically proven benefits. The following criteria should be considered when building your shoe collection:

1. Purchasing shoes in the afternoon: Because feet expand in volume throughout the day and under exertion, a running shoe purchase consultation should always take place in the late afternoon or evening to avoid selecting sizes that are too small.
2. Utilising lacing techniques: Specific marathon lacing techniques (heel lock lacing) allow the heel to be secured firmly within the heel counter without constricting the forefoot. This prevents the toes from sliding forward when running downhill.
3. Regular model rotation: Alternating among two to three different running shoe models with varying heel drops and last widths challenges the foot musculature in diverse ways and prevents monotonous overuse.
4. Rest periods for cushioning material: Between running sessions, the cushioning foam of a shoe requires at least 24 to 48 hours to fully regain its original shape. Daily use of the same shoe significantly accelerates material wear.
5. Meticulous hygiene and drying: Running shoes should be allowed to air-dry thoroughly after training. Internal moisture encourages the development of mycoses (athlete's foot and fungal nail infections).

Common mistakes

In clinical practice, runners regularly display misconceptions that lead to health problems despite the best intentions. Identifying these behavioural patterns is the first step towards lasting freedom from complaints.

A widespread misconception is the assumption that a shoe will widen significantly through breaking in. The basic structure of modern synthetic upper materials in running shoes barely stretches. A running shoe must offer adequate space in the forefoot area from the very first minute. If tightness around the toes is felt during fitting, the material will not yield even after many kilometres; instead, human tissue yields, forming pressure points.

Another mistake is uncritical adherence to a familiar shoe size. Manufacturers regularly modify last shape, upper material, or toe box geometry during model updates. A successor model may fit significantly tighter than its predecessor despite carrying an identical size number. Every pair must therefore be evaluated individually.

Excessively tightening shoelaces over the forefoot area is equally problematic. Attempts are frequently made to secure an overly wide or poorly fitting shoe by pulling laces extremely tight. This exerts heavy pressure on the extensor tendons and the nerves traversing the dorsum of the foot, potentially triggering painful tenosynovitis or localised paresthesia.

Finally, visual assessment of shoe wear is often used as the sole criterion. As long as the tread of the outsole remains intact, the shoe is erroneously deemed fully functional. However, microscopic fatigue of the midsole structure occurs within the interior of the foam and is usually invisible from the outside.

Current research and clinical perspective

Sports science and biomechanical research have re-evaluated many traditional assumptions regarding shoe selection in recent years. For a long time, preventive correction of pronation was considered the primary criterion when recommending running shoes. However, recent systematic investigations demonstrate that a mechanical pronation support does not generally reduce injury risk in asymptomatic runners [1].

Instead, scientific focus has shifted towards two concepts: the Preferred Movement Path concept and the Comfort Filter [2]. Research findings indicate that the human body intuitively selects the shoe geometry that minimises muscular effort and supports natural joint kinematics. When a shoe is perceived as comfortable and provides sufficient freedom of movement for the forefoot, this serves as a strong indicator of a biomechanically advantageous load distribution.

Studies investigating toe box width demonstrate clearly that toe constriction reduces force transmission during the push-off phase. Compression of the hallux decreases the activity of the flexor hallucis longus muscle and impairs the dynamic stability of the entire foot [3]. This corroborates the podiatric observation that narrow toe boxes not only cause local skin and nail damage but can also negatively affect the structural alignment of the entire lower extremity.

Regarding material fatigue, studies show that the shock-absorption capacity of EVA midsoles decreases significantly after 500 to 700 kilometres of running. Material compaction leads to higher peak impact forces being transmitted unmitigated to bone and joint structures [4]. This highlights the necessity of timely footwear replacement, irrespective of the visual condition of the upper material.

Treatment in Memmingen

Complaints arising from ill-fitting running shoes require expert and individualised assessment. At the practice FREITAG® Podologie GmbH at Kempterstr. 25 in Memmingen, we offer runners from Unterallgäu, Allgäu, and Upper Swabia comprehensive podiatric care. Further details regarding our facilities and directions can be found under /en/practice.

Whether precisely debriding painful pressure points, crafting custom silicone pressure-protection orthoses, or managing subungual haematomas and nail alterations medically, the objective remains restoring your pain-free load capacity. Additionally, for inflammatory tissue irritation, targeted application of cryotherapy can contribute to pain relief. Insights into the facilities of our integrated cryotherapy chamber are available under /en/cryotherapy.

If you are uncertain whether your current running shoes match your foot structures, or if you already experience complaints following training, schedule an appointment for a personal consultation. You can reach the practice team directly to arrange an appointment via our page /en/contact.