Stepping Back to Minimal Footwear

Applications Across the Lifespan

Irene S. Davis; Karsten Hollander; Daniel E. Lieberman; Sarah T. Ridge; Isabel C.N. Sacco; Scott C. Wearing

Disclosures

Exerc Sport Sci Rev. 2021;49(4):228-243. 

In This Article

Minimal Footwear in Older Adults

Minimal Footwear in Healthy Older Adults

Minimal shoes have been shown to be beneficial for older adults. Shoes with cushioning are likely to filter out important sensory information,[126,127] which is important for balance and stability, especially in aging populations. It has been shown that when sensory input is lost, such as through anesthetization of plantar afferent nerves, stability during quiet stance becomes impaired.[128] This may explain why balance during standing and walking in an elderly population is improved in minimal shoes compared with cushioned ones.[129] Second, although older adults tend to experience general lower extremity muscle weakening, there is a shift in joint power during walking gait from distal to proximal.[130] This suggests that foot and ankle function degrades with age, which may increase the risk for falls in this population.[131] Falls have been related to foot weakness,[132,133] and unfortunately, the intrinsic foot muscles (IFM) have been noted to become weaker with age.[134] Nearly one in four older adults experiences falls,[131] which are the leading cause of injury-related deaths in older adults.[135] Along with weakness and loss of function that accompany aging, chronic support of the foot can lead to further foot muscle weakening.[6,89]

It has been reported that standard features of conventional shoes can be detrimental to the elderly. For example, these shoes often have constrictive toe boxes, which has been associated with hallux valgus[136] (Figure 8). Other features, such as elevated heels, stiff uppers, and flared outer soles have been shown to negatively impact gait mechanics. For example, Aboutorabi et al.[137] conducted a systematic review of the effect of footwear on static and dynamic balance in elderly individuals. They reported that balance during standing posture and functional activities (i.e., the timed get up and go and functional reach tests) was improved when soles were thin and hard. This recommended footwear shares some characteristics with minimal shoes, such as thin soles, low heel-to-toe drop, low weight, and lacking sole flares.[138] Studies about the effect of minimal shoes on gait in this older population are still scarce. In one relevant study, Cudejko et al.[139] compared the center of pressure trajectory while older adults stood and walked in several footwear conditions. This included 11 variations of minimal shoes, a barefoot, and a conventional shoe condition. The older adults performed better on the timed up and go test with the minimal shoes compared with the conventional shoes The center of pressure excursion and velocity in the anteroposterior and mediolateral directions were also reduced during standing and walking in minimal shoes, indicating greater stability. Results between the minimal shoes and barefoot were similar. These collective results suggest that minimal shoes may offer a more stable alternative for healthy older adults.

Figure 8.

Comparison of Achilles tendon stiffness (as measured by the ultrasound velocity) between habitual rearfoot strike (RFS) and habitual forefoot strike (FFS) runners during walking (left) and running (right). Note the greater stiffness during both walking and running in the FFS runners. [Adapted with permission from (97). Copyright © 2019 Taylor & Francis. All permission requests for this image should be made to the copyright holder.]

Minimal Footwear in Older Adults With Knee OA

Knee OA is one of the most common musculoskeletal conditions of older adults. Although the etiology of knee OA is multifactorial,[140] mechanical aspects such as the intra-articular loads are the primary risk factors for its development and progression.[141–143] The external knee adduction moment (EKAM) is often used as a surrogate measure for these internal loads. Increases in the EKAM have been reported to increase the risk for the severity[144] and progression[145,146] of knee OA. Specialized footwear is an emergent conservative strategy to reduce EKAM. This footwear has included variable-stiffness soles,[147–150] rocker soles,[151] and laterally wedged insoles.[152–154] Although footwear with laterally wedged or arch support insoles results in a small reduction in the EKAM, this footwear type increases the frontal plane torques at the ankle. Preservation of normal ankle torques and kinematics is recommended to prevent adverse effects at the foot-ankle complex.[155]

Among footwear interventions to reduce knee joint loads, minimal shoes have been one of the most promising both in the short term[156–159] and long term.[160] Shakoor et al.[157] studied the acute effects of minimal footwear in patients with knee OA. The minimal shoe was custom engineered to mimic barefoot walking and was composed of a flexible poly carbon sole with flex grooves and a mesh top. They reported an 8% decrease in EKAM in a minimal shoe compared with self-chosen walking shoes and a 12% reduction compared with control (wearing a cushioned sports shoe). Others have compared the effect of a commercially available shoe, called the Moleca (Calçados Beira Rio S.A., Novo Hamburgo, RS, Brazil) shoe, to a modern heeled shoe on the gait of women with knee OA. The Moleca shoe (Figure 9) is a low-cost women's canvas flat walking shoe. It has a flexible 5-mm antislip rubber sole, and its mean weight is 0.172 ± 0.019 kg. These features qualify it as a minimal shoe.[109] In two cross-sectional studies, the Moleca shoe demonstrated reductions in EKAM of approximately 12% during walking and 15.5% during stair descent.[158,159] Trombini-Souza et al.[160] then conducted a clinical trial with older women with knee OA randomized into the Moleca shoe or a neutral athletic shoe and followed them for 6 months. They reported a 22% reduction in EKAM in the minimal shoe group: nearly double that of the study of the acute effects.[159] In addition, they experienced a 66% reduction in the Western Ontario and McMaster Universities Arthritis Index (WOMAC) pain domain, a 62% reduction in WOMAC stiffness domain, and a 63% improvement in WOMAC function domain. Pain medication also remained low and unchanged after 6 months. In stark contrast, the women in the control group experienced significant increases in EKAM (15.4%), WOMAC pain, stiffness, and a decrease in function. In addition, there was a 36% increase in the pain medication. Therefore, the minimal footwear resulted in less pain and better function than conventional footwear in patients with knee OA.

Figure 9.

Results of a minimal shoe (Moleca shoe, center) intervention in women with knee osteoarthritis (OA). Note improvements in the Western Ontario and McMaster Universities Arthritis Index (WOMAC), pain medication intake, external knee adduction moment (EKAM), stiffness, and pain compared with the standard shoe intervention.

Minimal Footwear for Individuals With Early Stages of Diabetes

Diabetes mellitus is a metabolic disorder that results in high glucose levels in the blood that eventually can damage both motor and sensory nerves. With time, diabetic peripheral neuropathy can ensue and cause major problems with the foot. Approximately 50% of diabetics experience neuropathy between 25 and 30 yr after the diagnosis of diabetes.[161] When it does develop, muscles become weakened and foot deformities, such as claw toes, can develop.[162] This can result in an anterior displacement of the already thinning fat pad, increasing the exposure to the metatarsal heads.[163] This, combined with the sensory loss, leads to ulcerations, most commonly at the metatarsal heads.[164,165] Most individuals with diabetic neuropathy are prescribed full contact soft foot orthosis and structured, cushioned shoes, often with a rocker bottom.[166] This intervention is aimed at redistributing the plantar load and reducing the load on the metatarsal heads. However, this intervention strategy is typically used for all patients regardless of their risk for ulceration or musculoskeletal status. Unfortunately, if used before the neuropathy progression, this passive approach might result in foot muscle atrophy,[6,89] leading to impairments in muscle strength and foot function. This can accelerate the degenerative changes that may occur.

Studies suggest that motor loss may occur before the sensory loss in the neuropathic process.[128,167,168] Diabetic neuropathy has been shown to affect both the intrinsic and extrinsic muscles of the foot.[169–174] The intrinsic muscles are small with short moment arms and primarily provide foot stability.[74] The larger extrinsic muscles can generate more force and with larger moment arms produce joint rotations. These muscles serve as prime movers of the foot.[74] Strength loss of both intrinsic and extrinsic foot muscles increases the risk for the development of foot deformities, which leads to an increased risk for ulceration.[164,175] Therefore, foot strengthening should be part of a diabetic treatment approach long before the neuropathy progresses. Studies of weight-bearing exercises that address the foot and ankle have shown improvements in range of motion, plantar pressures, and overall gait mechanics.[176–179] As a result, foot exercise prescription is now part of the International Working Group on the Diabetic Foot Guidelines 2019.[170]

Another way to encourage foot strengthening is through the use of minimal footwear in walking.[74] Minimal shoes are not currently recommended for those with diabetes due to the lack of support and cushion that a neuropathic foot requires. However, those diagnosed with diabetes typically have many years before a neuropathy progresses. This could provide a fairly extensive time for individuals to address the strength of their feet. Usage of minimal footwear during this early stage of diabetes may enable patients to maintain their foot motion and muscle strength for a longer period. This may help delay the development of foot deformities that can result in pressure ulcerations. Minimal footwear coupled with a foot strengthening program may provide a way for individuals to maintain foot strength and function before development of neuropathy. These feet might be more resistant to dysfunction if the neuropathy develops. This type of a program would need to be monitored by a medical professional who could routinely assess the sensory and motor status of the individual.

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