They apply more effort! More effort, when applied at the appropriate time during the casting stroke, is a great thing and can certainly add distance when needed. However, a great casting stroke is built on timing.
Watch some of the greatest casters in the world, and the fluidity of their stroke along with their ability to properly time the backcast transitioning into the forward cast are what make them so proficient.
Today's episode marks day 14 of 21 Days of Fly Fishing Education, and discusses three actionable tips for increasing the distance in your casting stroke.