Atenolol is a beta blocker to stablize the heart rate. I'm not sure of the numerical values you have posted as medical significant, but I've been taking coreg (beta blocker) for more than 7 years and I can't get my HR above 120 (systolic).
At your age 116 might be adequate for an aerobic excercise, you may want to consult with a professional physiologist for the proper exercise therapy or contact the doctor who prescribed the medication to get an idea of the expectations for the medication and exercise parameters.
Thanks for your question, and if you have any further questions or comments you are invited to respond. Take care,
Ken