In my Crealde Urban Sketching class, we take one class to do fast five or ten minute poses with each student taking a turn.
As a demo I sketch each student in turn and try and encourage the students to capture more that the person but the entire scene.
There is a frantic energy to working so fast and the goal to get the students to work just as fast and frenetic. Sketches become less detail oriented and more simplified. Detail is only added where it is needed.
I am always pushing students to look for the curve of the back so in this sketch there is one curve drawn behind the figure to show that curve. It was the first line to go on the page.