As you may know, in deciding which papers to publish we have to make an editorial judgement about the immediacy of interest to our readers and the degree and nature of the advance demonstrated. In practice, this means that we decline a majority (and ever increasing proportion) of manuscripts without sending them to referees, in cases where we feel that, even if referees were to certify the manuscript as technically correct, there would not be a sufficiently strong case for publication in Nature Physics. I am sorry to have to say that we must take this view concerning your submission.
In the present case, we have no doubt that your mathematical description of the dynamics of human walking will be of inherent interest to fellow researchers working on this and related topics. However, I regret that we are unable to conclude that your paper provides the sort of new fundamental or general insight in physics, with sufficiently broad implications, that would excite the interest of a wide, non-specialist audience of physicists. Therefore, we feel that the paper would find a more appropriate home in a specialist journal.
Although I regret that we cannot offer to publish your paper in Nature Physics for editorial reasons, it may be appropriate for our sister journal Nature Communications, and we encourage you to transfer it there. If you would like to do this (or transfer to a different Nature Portfolio journal), a link to initiate the process can be found in the postscript of this email. Please note that the editorial team at Nature Communications would consider your manuscript independently of our suggestion to transfer. Also, please note that Nature Communications is a fully open access journal.
We are sorry that we could not be more positive on this occasion, but we thank you for your interest in the journal. Please understand that our decision does not reflect any doubts about the quality of the work reported, and I hope you will rapidly receive a more favourable response elsewhere.