When figure drawing, you will find that the most spontaneous and immediate drawings you produce are during the gestural drawings. During the gestural drawings you will aim to produce rapid sketches of the model based on careful observation; recording as much information about the pose as possible in a very short amount of time. The short time allocated for gestural drawings imposes a need to produce rapid sketches that capture and express the most important characteristics of the form, posture and action of the subject being portrayed, they do not aim to produce a detailed drawing of the aesthetic.
Scheduling time for rapid sketches in a life drawing class is standard across the industry, there are many reason for this, but arguably most significant is the need provide an important opportunity for artists to exercise careful observation of the nude figure. Gestural drawing is an essential exercise in gaining vital skills as an artist of practising careful observation while co-ordinating what observe with your drawings. By making rapid sketches of the life model you will acquire skills that will inevitably be reflected in even the most elaborate and complex drawings you may aim to produce, after all in order to draw well, it is fundamental to understand what you are seeing.
When I produce a gestural drawing, I carefully observe the entire figure; noting the posture and form of the model. To do this I assess the axes of the internal structure, especially the position of the spine and pelvis; the areas of tension between the various body parts (where they are placing weight or holding pressure on groups of muscles and how the model is balancing) as well as the direction of the movement or gesture.
If you haven’t tried gestural drawing before, I highly recommend using this exercise either at the beginning or end of a life drawing session. Regularly carrying out this exercise will result in you producing drawings that not only depict the posture of the model but also the psychological aspects of the pose.