Strong lines define the dynamic forces that the eye perceives when it looks at a subject. To use an example, if you watch a boxer giving a punch, you will only very quickly, see the group of muscles in action to achieve this gesture. However, you will be able to feel the movement really well and itís this ability that we are going to concentrate on.
Letís take a specific example and look at the first drawing of this man running. Though this drawing, that loyally reproduces the photograph, is anatomically and gesturally correct, he is static, as if on a piece of paper. The reason for this is simple: the illustrator has simply reproduced what he could see, without trying to give it an impression of movement.
To give it movement, letís look at the drawing and find the main strong line, that will allow us to get to figure 2, representing the main movement; in other words, the movement of the body, through the left foot. Then letís look for the other strong lines, or what could be called the secondary movements or induced movements. Once these have been found, letís have fun redoing the drawing, whilst forcing ourselves to keep the strong lines that we found beforehand. These will need to be our guidelines that we can still feel once the drawing has been finished. We can then see that this drawing, which was based on the first drawing and essentially covering the same movement, has much more life in it.
Letís study other examples, like the boxer in action. We tend to think of a punch as a straight line, but the straight line will be too neutral, as shown by the first arrow. The second arrow shows the rhythm of the arm, or how to use the anatomy to give life to a body, by playing with curves. The last arrow, which reproduces the main dynamics of the arm, shows that the strong line of the arm is far more expressive than a "simple" right hook.
Letís then focus our attention on the nude, in order to see how anatomy creates a group rhythm, that gives life and charm to a body.
For this last example, I have used a dancer in action, as the model and I have only drawn the strong lines of the body and dress. Please donít hesitate to do these two types of sketches, as well as quick sketches, in order to understand the strong lines of the human body and their influences on clothing.