6-Minute Walk Test reference equation for individuals with Class III obesity in the U.S.: a comparison with an Italian cohort.

Purpose: This study aimed to develop a U.S.-specific reference equation for the 6-Minute Walk Test (6MWT) in individuals with Class III obesity and compare its performance with the Italian model by Capodaglio et al. The goal was to provide clinicians with a more accurate tool for assessing functional capacity.

Methods: A retrospective review was conducted on 307 adults with Class III obesity referred to outpatient physical therapy from 2017 to 2023. Of these, 295 completed the 6MWT. Multiple linear regression was used to build a predictive model using age, sex, and BMI as independent variables. The model was validated internal cross-validation and compared with Capodaglio et al.'s equation. Subgroup analyses by age group were also conducted.

Results: The final model included age, BMI, and gender, explaining 41% of the variance in 6MWT distance. The mean absolute error was 53.2 meters, and the Spearman correlation was 0.67. Compared to Capodaglio's model, ours predicted 6.52% lower distances overall, with the largest differences in adults over 60.

Conclusion: The new U.S.-based model provides more accurate 6MWT predictions for individuals with Class III obesity, particularly older adults. It may help guide functional assessment and pre/post-metabolic and bariatric surgery care in this population.