A common misconception of the arm swing at max velocity is that it will help propel the athlete horizontally, increasing stride length. Think of two people hooked up by a single rope and they were told to run in opposing directions. Assuming both people were running at the same velocity, once the rope reached it’s full length, the middle of the rope wouldn’t have moved in either direction. Just as both arms are synchronized in sprinting, any horizontal propulsion you could be gaining from the front-side arm, will be muted by the back-side arm due to the opposing momentum that each arm is creating.
Arm-swing can, in fact, aid in vertical propulsion. In contrast to the cancellation of horizontal propulsion, both arms are synchronized in a vertical direction at toe-off. Because of this, arm swing can aid in up to 10% of vertical propulsion.
Trying to artificially enhance arm swing could be very detrimental to sprint mechanics seeing as the arms really don’t play a major role. The outcome of vertical propulsion is from a rhythmic arm swing. So rather than try to “reach” with the arms, it’s better to allow the arms to stay rhythmically in balance with the legs during max velocity.