How close do the Heart Rate and RER match from my VO2max test? There is a pretty clear relationship. Here’s a graph of heart rate (x-axis) to RER x 100 (y-axis).
Point 1 is the actual point where my RER crosses over from pure fat burning and starts to burn a small amount of glucose. This correlates to a 118 bpm of heart rate.
Point 2 is the best linear fit and is pretty close to point 1. The fit of the entire line is really good with an R^2 of 0.9775.
My MAF number is 122 which is a bit higher and into the carb burning range. At the MAF number my RER would be around 0.72. That might explain why my blood glucose dropped a bit with my last 1 hour walk in the MAF range (from 105 before the walk to 87 after). I was burning some glucose.
Here is the chart of my Heart Rate vs RER and %Fat/%Carbs. Your mileage will vary.