Sure, some (not a huge fraction, I'm guessing single digit percentage) of very physically active people are poorly modeled by BMI but it shouldn't matter if the

Sure, some (not a huge fraction, I'm guessing single digit percentage) of very physically active people are poorly modeled by BMI but it shouldn't matter if they are explictly handling these covariates. It's more an issue if there is something they haven't accounted for, as they point out.