Estimating Target Heart Rate Zone (THR)

220-age (years) = age adjusted maximal heart Rate (HR)

Example for 20 year old person

220-20= 200 beats/min

70% maximal HR = low end of THR zone

.70 X age adjusted maximal heart Rate (HR)  = low end of THR zone

.70 X 200 = 140 beats/min

This is the low end of your THR

85% maximal HR = high end of THR zone

.85 X age adjusted maximal heart Rate (HR)  = high end of THR zone
.85 X 200 = 170 beats/min

When you workout you should keep your heat rate between these 2 rates for maximum cardiac benefit.