Life Fitness 8500 Operation Manual page 20

Defined by the American College of Sports Medicine's "Guidelines for Exercise Testing and Prescription" as equal to
†
220 minus an individual’s age.
* Target Heart Rate (THR) is a percentage of the theoretical maximum. For example, a 40-year-old user's THR for the HEART
RATE HILL workout is 144. This workout targets 80 percent of the maximum, so the equation would be (220-40)*.80=144.
A 20-year-old user’s THR is 160, so the equation would be (220-20)*.80=160.