So, here’s how it would work for a 40-year old person:
40 multiplied by 0.88=35.2
170.8 multiplied by 0.65= 111.02 (the low end of the target heart rate range)
170.8 multiplied by 0.85=145.18 (the upper end of the target heart rate range)
So a 40-year old’s target heart rate would be 111 to 145. Always check with your doctor before beginning an exercise regime.