Kacy, DO NOT use target heart rate formulas for people who are on beta blockers or any other med that slows down heart rate. They won’t work. I agree with Karin and Natalie 100% – Use the RPE scale (0-10 version) and the Talk Test. These will be better.
While the 6-20 RPE scale can give an idea of exercise HR, its irrelevant in this instance since they are on Beta Blockers. I like the 0-10 scale since its easier to understand for most people.
I teach personal training and I instruct trainers to forget what the textbooks say about target heart rate. I don’t like it as the main mode of gauging exercise intensity.
The RPE scale and Talk test will work with 99% of your clients too -not just the people with blood pressure/heart problems.