A drawn runner never physically moves across the page. Yet a few lines can make the panel feel as though the character is rushing forward, the background is passing or the viewer is being pulled towards an impact.
Look first at the direction of the lines. Do they run parallel behind the figure, converge towards a point or radiate away from it? Each arrangement guides attention differently, and the surrounding panels help establish what is actually moving.
Find a short sequence in a legally obtained manga. Identify where the environment is shown clearly and where it becomes simplified into motion marks. The detailed panel may establish the space that lets a later panel omit the background without losing the action.
Notice whether the figure remains sharply drawn while the surroundings become lines. That can create a different emphasis from a blurred or repeated figure against a relatively stable setting. Treat this as an observation of the specific page, not a rule every artist follows.
Try a small original drawing
Draw a simple invented figure moving towards a doorway. Make two versions with the same figure and framing. Leave one background still; add a restrained set of directional lines to the other.
Ask what changed. Is the direction clearer? Did the marks cover an important hand or object? Did the panel become more energetic but less readable? More lines do not automatically make a better action image.
Speed lines can also emphasise a sudden reaction or dramatic focus rather than literal travel. Read the expression, lettering and sequence before deciding that every mark represents physical velocity.
When discussing the page, describe the effect precisely: “The lines draw my eye towards the doorway” explains more than “This looks dynamic.” It also gives you something useful to test in your own original art without copying a published character or panel.