September 2019

Association Between Running Shoe Characteristics and Lower Extremity Injuries in United States Military Academy Cadets

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By Gary Helton, PT, DSc, SCS, OCS

Running-related overuse injuries are very common among recreational runners with the reported annual injury rates ranging from 39% to 85%. There are few large prospective cohort studies investigating injury risk associated with different running shoe characteristics and they are often contradictory. Our goal was to prospectively investigate the relationship between running shoe characteristics and lower extremity musculoskeletal injury with a hypothesis that there would be an increased risk of injury associated with individuals wearing shoes with minimal torsional stiffness and heel height when compared to those wearing shoes with greater levels of torsional stiffness and heel height.

This large-scale prospective cohort study included 1025 incoming cadets with 827 participants included within the final analysis. Shoe torsional stiffness and heel height were calculated and recorded using a novel torsional shoe stiffness device designed and manufactured for the specific purposes of this investigation (see Figure). Lower extremity injuries sustained over 9 weeks during cadet basic training were documented. Kaplan-Meier survival curves were estimated with time to incident lower extremity injury as the primary outcome by level of the independent predictor variables. Risk factors or potential covariates were carried forward into multivariable Cox Proportional Hazards Regression Models. Also, absolute and relative risk reduction and numbers-needed-to-treat were calculated.

Approximately 18.1% of participants incurred a lower extremity injury with a median time to lower extremity injury of 15 days. Cadets wearing shoes with mild and moderate lateral torsional stiffness were 36% and 49% less likely to incur a lower extremity injury than cadets wearing shoes with minimal lateral torsional stiffness, both statistically significant observations. Injury risk was statistically similar among cadets wearing shoes with minimal and extreme lateral torsional stiffness; however, those wearing shoes with extreme lateral torsional stiffness were still 21% less likely to incur a lower extremity injury than those wearing shoes with minimal lateral torsional shoe stiffness. Cadets wearing shoes with mild and moderate heel height were 39% and 31% less likely to incur a lower extremity injury than those wearing shoes with minimal heel height, observations likely of clinical importance yet not statistically significant. All observations were made with the influence of gender, ethnicity, and history of injury controlled.

Shoes with mild to moderate lateral torsional stiffness and heel height may be appropriate in reducing risk of lower extremity injury in cadets. Shoes with minimal lateral torsional stiffness should be discouraged in this population. Risk reduction analyses indicated that one only needed to treat 8-11 people with a shoe with mild to moderate lateral torsional stiffness and heel height to prevent 1 lower extremity injury.

The observations of this study have important implications for shoe wear policy and recommendations within the military and athletic training environment. Other agencies that conduct training similar to the military may want to consider avoiding the extremes of lateral torsional stiffness and heel height as well. Last, this study provides guidance for shoe manufacturers that can be used to manufacture shoes less likely to contribute to injuries within the military and athletic training populations.

Source: Helton GL, Cameron KL, Zifchock RA, et al. Association Between Running Shoe Characteristics and Lower Extremity Injuries in United States Military Academy Cadets. J Sports Med. 2019; 2019;doi: 10.1177/0363546519870534. Epub 2019 Sep 9.

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