How Do Novice Runners With Different Body Mass Indexes Begin a Self-chosen Running Regime?

BACKGROUND: Overweight and obese novice runners are subjected to a higher load per stride than their normal-weight peers. Do they reduce their running dose accordingly when beginning a self-chosen running regime? OBJECTIVES: To describe and compare the preferred running dose in normal-weight, overweight, and obese novice runners when they commence a self-chosen running regime. METHODS: In this exploratory, 7-day prospective cohort study, 914 novice runners were categorized into 1 of 3 exposure groups, based on their body mass index (BMI): (1) normal weight (BMI less than 25 kg/m ², n = 405; reference group), (2) overweight (BMI of 25 to less than 30 kg/m ², n = 341), and (3) obese (BMI of 30 kg/m ² or greater, n = 168). All runners were equipped with a globalpositioning- system running watch, which provided information about distance, duration, speed, and date of each running session during the first week of a self-chosen running regime. RESULTS: During the first session, overweight runners (difference, -0.5 km/h; 95% confidence interval [CI]: -0.8, -0.2 km/h; P<.05) and obese runners (-1.7 km/h; 95% CI: -2.0, -1.4 km/h; P<.05) ran slower than normal-weight runners. Obese runners also ran a shorter distance compared to normalweight runners (-0.4 km; 95% CI: -0.7, -0.2 km; P<.05). During the first week, overweight runners (-0.5 km/h; 95% CI: -0.7, -0.2 km/h; P<.05) and obese runners (-1.7 km/h; 95% CI: -2.0, -1.4 km/h; P<.05) ran slower than normal-weight runners, while running distance and duration were similar. CONCLUSION: Overweight and obese runners selected a similar training dose to that of normal-weight runners when starting a self-chosen running regime. This may partly explain the higher running-injury risk among overweight and obese runners compared with normal-weight runners observed by other studies.