Effects of footwear and stride length on metatarsal strains and failure in running

Anita Fung,W Brent Edwards,Colin R Firminger,Lindsay L Loundagin

doi:10.1016/j.clinbiomech.2017.08.006

Abstract

BackgroundThe metatarsal bones of the foot are particularly susceptible to stress fracture owing to the high strains they experience during the stance phase of running. Shoe cushioning and stride length reduction represent two potential interventions to decrease metatarsal strain and thus stress fracture risk. MethodsFourteen male recreational runners ran overground at a 5-km pace while motion capture and plantar pressure data were collected during four experimental conditions: traditional shoe at preferred and 90% preferred stride length, and minimalist shoe at preferred and 90% preferred stride length. Combined musculoskeletal – finite element modeling based on motion analysis and computed tomography data were used to quantify metatarsal strains and the probability of failure was determined using stress-life predictions. FindingsNo significant interactions between footwear and stride length were observed. Running in minimalist shoes increased strains for all metatarsals by 28.7% (SD 6.4%; p<0.001) and probability of failure for metatarsals 2–4 by 17.3% (SD 14.3%; p≤0.005). Running at 90% preferred stride length decreased strains for metatarsal 4 by 4.2% (SD 2.0%; p≤0.007), and no differences in probability of failure were observed. InterpretationsSignificant increases in metatarsal strains and the probability of failure were observed for recreational runners acutely transitioning to minimalist shoes. Running with a 10% reduction in stride length did not appear to be a beneficial technique for reducing the risk of metatarsal stress fracture, however the increased number of loading cycles for a given distance was not detrimental either.

Highlights

Stress fractures are considered overuse injuries associated with the mechanical fatigue of bone.Long periods of repetitive loading, such as that incurred during running, leads to the formation of bone microdamage, or microcracks (Burr, 1997)
Metatarsal stress fractures have been observed in minimalist shoe runners (Cauthon et al, 2013; Salzler et al, 2012), it must be noted that prospective evidence linking an increased incidence of metatarsal stress fracture to minimalist shoe running does not exist
A recent biomechanical study has demonstrated increased forefoot loading and plantar pressure when running in minimalist versus traditional footwear (Bergstra et al, 2014), and our work further illustrates that running in minimalist shoes is associated with increased tissue-level strains at the metatarsal diaphysis

Summary

Introduction

Long periods of repetitive loading, such as that incurred during running, leads to the formation of bone microdamage, or microcracks (Burr, 1997). If the rate of microdamage accumulation exceeds the rate of bone remodeling, these microcracks may propagate to a critical length (O’Brien et al, 2003), thereby increasing the risk of stress fracture. The formation of microdamage in bone, and the number of repetitive loading cycles it may endure prior to failure, is a strong function of strain magnitude (Carter et al, 1976). The metatarsal bones of the foot are susceptible to stress fracture owing to the high strains they experience during the stance phase of running. Shoe cushioning and stride length reduction represent two potential interventions to decrease metatarsal strain and stress fracture risk

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