In fly casting, there is a direct correlation between the length of aerialized fly line and the length of the casting stroke. For the most proficient technique, there must be a corresponding lengthening of the casting stroke as the amount of line in the air is increased. In other words, a long length of line requires a long casting stroke while a shorter line calls for a stroke that is proportionately reduced. Furthermore, as the stroke increases in length, the casting arm should progressively extend a greater distance in front of the body on the forward cast and further beyond the elbow on the backcast.
By adjusting the length of the stroke to the amount of line in the air, you have a far greater potential to build more line speed, flex the rod deeper into its powerful butt section; and make longer casts with significantly less effort than if you rely on the same short, abbreviated motion all the time regardless of the amount of line you are handling. The inherent fluidity produced by lengthening the stroke also makes it much easier to form smooth, slack-free, and aerodynamic loops than if you always use a constricted stroke with its abrupt and jerky nature. To make consistently efficient casts at all distances, the concept of “long line, long stroke; short line, short stroke” is a good one to follow.