You are treating a patient with cardiac disease who rates the intensity of her exercise as a 12 using Borg's Original Rate of Perceived Exertion (RPE) Scale. Which of the following percentage of the patient's age-adjusted maximum heart rate best corresponds to a rating of 12 on the exertion scale?
1. 60
2. 70
3. 80
4. 90
The solution will be posted in a few days.