Oh no, Pikachu on a rampage!!!

First of all instead of using % of max HR, use heart rate reserve (HRR). Take your max HR, subtract your resting heart (just before the workout). Take your goad percentage of that number (85-90%) then add your resting heart rate back in. This is a better number to use. If you want to improve VO2 consumption, you have to workout near or above 85-90% of HRR depending on your current fitness. To improve overall endurance, including the bodies ability to burn fat and carbs more efficiently, it is important to do those long slower rides. But unless you put intervals in your workout, the long slow rides will not improve VO2max. Does that help?