Considerations in the Selection of a Running Shoe

Introduction

The rapid growth in the participation of running for health and competition has contributed to the exponential demand for running shoe production and development. Over the past 50 years, running shoes have evolved from a minimal design to highly cushioned and supportive to light, partial minimalist shoes. Numerous athletic footwear companies have emerged to respond to the demand for the range of products that fit the needs of the growing market. Purchasing a running shoe can be very overwhelming for the typical runner; store displays are flooded with shoes of different weights, designs, features, and materials and prices. Information sources for shoe selection are not often based in evidence. The consumer is left either to decide for themselves which shoe they like or to be dependent on a salesperson or other individual to select for them. The challenge for clinicians who advise patients on running shoe use is staying abreast of the continuous updates in footwear and the rapidly changing scientific landscape of shoe benefits and risks to help runners make more informed choices. This chapter works to provide evidence-based tips for helping runners select running shoes.

Key Shoe Characteristics on Gait

The foot is an engineering marvel, as it contains 26 bones, interconnected with a large network of muscles and ligaments, tendons, and fascia. Clinically, the most important point to remember is that running shoes need to be thought of as protectors of the plantar surface of the foot from injury against the environmental surface, and not as replacers of muscle efforts of the foot and lower limb. Shoes should also not interfere with the normal load-bearing functioning of the musculoskeletal structures of the foot. The foot senses contact surface characteristics, has kinesthetic awareness, and acts as an arch to distribute mechanical forces during load bearing. Shoes can modulate the foot actions between the body and the environment. There are several types of running shoes:

• 1)

  Trainers—the vast majority of running shoes, which are meant to protect the runner from the ground and resist wear to last for many miles

• 2)

  Light trainers—lightweight versions of the trainer that may help speed, and thus, shave off potentially seconds from race times depending on the race distance

• 3)

  Racing flats—built strictly for speed and have the capacity to take up to 30–40 s off a 10K time

• 4)

  Trail shoes—highly durable, breathable running shoe meant for rugged terrain

We will more completely analyze “trainers,” which comprise the majority of shoes used by consumers. Key characteristics that can modify the foot interaction with the ground include sole stiffness, sole thickness (sole thickness at heel and toe and difference between the two which is termed heel-to-toe drop), structural stability/motion control or offloading components, toe box width, and shoe weight.

Sole stiffness. The lower limbs can adjust springiness and stiffness in response to contact with different running surfaces. For example, when running on hard surfaces, the muscles of the leg work harder to increase compliance, whereas running on softer surfaces triggers increased leg stiffness. But wearing shoes of different stiffness properties can change the interaction between the leg and the ground and thus the mechanical loading on the body. Vertical peak impacts increase as the shoe midsole softens, indicating that more cushioning is associated with harder landings. Softer footwear slows the exchange of momentum and increases the time duration of the impact, subjecting the runner to higher vertical forces for a longer time. Higher impact forces have been linked to injuries, including patellofemoral pain syndrome, stress fractures, and plantar fasciitis. Moreover, the softer the sole of the shoe, the greater the risk for abnormal mechanics such as exaggerated foot pronation.

Sole thickness. The thickness of the midsole can change how and how long the runner contacts the ground. The distribution of that sole thickness from under the heel and toe also changes running motion. Evidence shows that runners who are habituated to run with minimal shoes with thin soles land on the ground more softly than runners who run partially in minimal shoes. Vertical and resultant load rates are lowest among runners committed to minimal shoewear, but these loads are increased even if a runner is habituated to a small amount of cushioning. The overall thickness can also increase ground contact time. This effect is most pronounced when shoes have relatively high thickness at the heel (≥24 mm) and a 12-mm heel-to-toe drop compared to less thick shoes with less change in thickness from heel to toe (0–5 mm drop). With respect to initial foot impact position, the foot strikes with a more plantarflexed position in shoes with minimal heel-to-toe drop compared with larger drop values. This plantarflexion effect is favorable, as significant dorsiflexion (more heel strike) at initial impact can be related to higher impact forces and loading rates. Moreover, less or minimal cushioning in running shoes may facilitate ankle and foot proprioception during running; minimal shoes improve kinesthetic sense and ability to sense when the foot makes contact with the ground. Finally, shoes with less cushioning can effectively increase intrinsic foot muscle strength.

Structural stability or motion control components. Some commercially available shoes contain structures that modify the foot motion to help improve foot posture, provide stability, and prevent pronation during loading. These structures include polyurethane components in the arch, medial posts, or different layers of foams of varying stiffness. Runners with obvious overpronation may derive transient injury risk reduction benefit from motion control shoes but not runners with neutral or supinated feet. However, most evidence indicates that neutral shoes can be safe for runners even with excessive pronation. Other designs include lateral wedges that are crafted to change knee alignment and lessen medial knee forces. Wedges or thick shoe inserts in theory do offload the knee. However, from the clinical perspective, there is a mechanical trade-off of changing natural foot motion with extra structures in the shoe. One must consider that changing the pronation and foot eversion with motion control shoes may create secondary unintended loading effects on other areas such as the tibiotalar joint and the knee. Rearfoot striking also becomes more prominent with motion control features in the arch. Use of shoes with medial posting or support structures restrict the natural spring motion of the foot arch to dissipate loading forces during running. Restriction of arch flattening during normal loading also interferes with impact dampening and recoverable energy strain in the elastic tissues. Importantly, the motion control features of running shoes can reduce the engagement of intrinsic foot muscles and perpetuate foot weakening over time. Shoes that are described as “neutral” allow the natural pronation and supination to occur during the gait cycle.

Toe box width. During different phases of the gait cycle from initial contact, the foot naturally transforms from a compliant structure to a rigid lever at push-off. Upon foot contact, the mediolateral arch drops in a controlled manner and widens the plantar surface of the foot to help distribute the loading across the metatarsals. At midstance, both the mediolateral and longitudinal foot arches depress, the metatarsals splay, and the weight of the body is supported by the network of intrinsic foot muscles and muscles about the ankle. Foot morphology also changes after long runs, such that ball width, girth, and foot volume all increase and arch height decreases. Restriction of the natural foot deformation and midforefoot widening can (1) change the loading distribution and forces occurring in the foot during stance and (2) create running-related repetitive loading issues such as interdigital neuromas, metatarsalgia, bunions, and painful toenails. Shoes with narrow toe boxes or more pointed forefoot shape increase pressures on the medial aspect of toes and forefoot and increase pressure and shear stress under the second metatarsal head.

Shoe weight. The main effect of shoe weight is on running economy, defined as the amount of oxygen or energy used to run at a specific work rate. Heavy shoes require more energy to move than light shoes. Among the various shoe types on the market, the elevation in oxygen cost while wearing rocker bottomed shoes during running compared with standard running shoes and minimalist shoes ranges from 4.5% to 5.6%. Adding mass to the shoes can increase metabolic rate by 1.11% for every 100 g of shoe, and the energy cost increases proportionate to the weight. This is problematic for competitive runners since the extra weight degrades distance running performance during a time trial event. Commercial shoes are not adjusted for a runner's body weight; thus, heavier shoes exert a greater relative metabolic effect in runners of smaller body weight. Over the course of a long distance event, lighter shoes may confer energy savings and protect against muscle damage compared with heavy shoes.