The authors have introduced the topic well, and covered the importance for using alternative measurement methods which are necessary in clinical settings where standing height is not possible. It would be better to describe the study population as being in ‘late adolescence’, as puberty can begin at a much earlier age than 15 years. It is important for the authors to note in the paper that adolescents have not yet reached their growth potential and therefore long bones lengths such as those measured in the ulna length will be impacted by these growth changes.
The methodology was well described and the statistical tests used were appropriate for the study objectives. The authors need to describe what they mean by ‘weight status’.
The results and discussion are well written and identify the potential for using ulna length as a surrogate measurement method. It would be interesting to add a bit more on the gender differences identified in the study, as well as differences identified between the ethnic groups.

The authors have made appropriate changes. No new comments.