Abstract: OBJECTIVE: To investigate the association between weight loss before joining the U.S. Army and rates of musculoskeletal injury (MSKI) during physically demanding Basic Combat Training (BCT). METHODS: Self-reported weight loss was collected on 3168 Army trainees who were followed through electronic medical records for diagnosis of any and region-specific MSKI. Cox regression models were stratified by sex and COVID-19 pandemic and adjusted for age, height, maximum-ever BMI, race/ethnicity, smoking history, prior physical activity, and history of injury. RESULTS: A total of 829 trainees (26.16%) reported losing weight to enter the Army with mean (SD) weight loss of 9.06 (8.62) kg, most commonly through exercise (83.72%). Trainees who lost weight to enter the Army had lower rates of any (HR: 0.86; 95% CI: 0.74, 0.99) and lower extremity (HR: 0.84; 95% CI: 0.72, 0.98) MSKI during BCT compared to trainees who did not lose weight. Rate of weight loss (mean [SD]: 1.27 [1.06] kg/week) was not associated with any or region-specific MSKI. CONCLUSIONS: Results indicate that losing excess weight before military training may minimize injuries during training and the relatively gradual rate of weight loss in these trainees did not pose a higher risk of injury.