For stress tests purposes ( regular treadmill and nuclear exercise imaging) physicians typically use the formula : Maximal heart rate =220-age.
Another formula is the Tanaka formula; Maximal heart rate =209-.7age
More recently based on a Norwegian study by Nes and co workers the following formula is suggested :
Maximal heart rate= 211-.64 with an error term of +/- 10.8. See here for reference.
For the three formulas applied to a 75 year old we get maximal heart rate predictions of
145,156 and 163 . (Standard,Tanaka,Nes)
Frequently stress tests are terminated at when the patient reaches 85% of the predicted max heart rate.
For the three formula we get :
The validity of a stress tests depends in part on having the patient exercise to a high enough level to induce some degree of stress into the stress tests and use of 220-age formula would seem to make false negative tests more likely.This is not breaking news, Tanaka said as much in his 2001 article in the American College of Cardiology Journal but still some stress test facilities still use the 220 formula . See here.