Draw a line about a yard long on the pavement. Walk 30 feet forward and draw a similar line on the ground. Set up two markers -- which can be small blocks of wood -- behind the furthest drawn line.
Crouch down in the middle of the line without markers. Have a friend say, "Go." Run to the opposite line as fast as you can..
Pick up one of the markers when you reach the line 30 feet away.
Turn and sprint back to your original line and drop the marker behind the line.
Run again to the opposite line and after picking up the second marker, sprint back to the original line. Drop the marker. This constitutes one repetition.