Footnotes

• Twitter @NicolaPhillPT, @physiocolinp

• Contributors Both authors contributed equally to the manuscript, including writing and creating the model illustrated.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Patient consent for publication Not required.

• Provenance and peer review Not commissioned; externally peer reviewed.