|RER represents respiratory exchange ratio. This is the ratio of CO2 expired to O2 consumed
Predicted (or estimated) maximum heart rate is 220-Age. So, a predicted maximum heart rate for a 20-year-old student is 220-20=200 beats per min. Remeber, we look at heart rate in beats per min.
Plateau of VO2 means the following: A maximal aerobic test progressively gets harder for the sujbect. When the oxygen consumption (VO2) plateaus < 150 ml/min VO2 as the test continues to get harder it is very good indicator that the subject is at or near their actual VO2max capacity.
Note the Rating of Perceived Exertion chart below. It shows an example of the %intensity with each number. The two anchors are 6 (which is very quiet seated rest) versus 20 (which is the point of exhaustion from working as hard as you can).
Although VO2peak varies from textbook to textbook, for PEP326L a VO2 peak test is when a subject gives a maximal effort in an aerobic capacity test but does NOT attain the VO2max criteria. It means the subject worked as hard as she/he could, but did not attain the VO2max criteria.