What is the difference between a vertical and a horizontal relationship?

vertical is on the y-axis and is the output (range) while the horizontal is the x-axis (domain).

the more fit you are, the faster the recovery. your heart rate drops most sharply in the first minute after you stop exercising; it should then fall about 20 beats a minute—a drop of less than 12 beats a minute is considered abnormal. this “recovery heart rate” is measured as part of an exercise stress test.