Background Risk factors for ultramarathon injuries are poorly understood.

Objective Effects of human and environmental factors on predicting injuries.

Design Observational study using electronic surveys prior and 10-days post-race.

Setting Leadville-100 is a difficult high-altitude trail ultramarathon (160.9 km) with a course elevation of 2804–3840 m in Leadville, Colorado.

Participants All runners completed the pre-race survey and half (n=308, 48%) completed the post-race survey.

Assessment of risk factors The dependent variable was visiting a physician/health care provider for injuries due to the race. The independent variables were age, gender, prior completion of the race, foot type (normal, flat feet, high arch), Body Mass Index (BMI), height, weight, wearing orthotics, shoe type, changing shoes during the race.

Main outcome measurements The primary outcome measure was whether stability running shoes are correlated with fewer injuries compared to other types of shoes.

Results Out of 646 participants, 361 (55.9%) runners finished the race under the 30-h time cut-off. Majority (n=676, 84.9%) were male with average age of 41 years (range 21–73). Majority were first time participants (n=468, 73%). Among those who completed the post-race survey, 109 (35%) visited the aid stations during the race and 37 (12%) sought medical attention after the race. Runners primarily visited aid stations for musculoskeletal, gastrointestinal, and respiratory complaints. Half (n=171, 55%) were able to walk without assistance and majority (n=216, 72%) return to work after 1 day of rest. Runners with cushion shoes were more likely to seek medical attention compared to those with instability shoes (p<0.005; OR=3.59; CI 1.33 to 9.66). There were no correlations between gender, foot type, BMI, height, weight, having orthotics, and prior race completion and seeking medical attention post-race.

Conclusion Compared to other running shoes, the stability type is correlated with fewer injuries requiring medical visits among participants in a high-altitude ultramarathon.