If you find out after the session that it was too hard or too easy you may be too late. I will start my session off by describing a modified version of the RPE. To find out what their pain tollerence is I will explain what the scale is, what the numbers represent and start them on a controlled modality (treadmill, elliptical). I will watch how their heart rate responds to intensities ask them what number they feel they are at and then check the HR monitor to see where they are actually. This helps me to understand how they respond to exercise intensities to ensure a positive experience.