During any sort of moderately intense workout, you will probably see your MyZone app putting you somewhere in the yellow or red zone. These zones signify that your heart rate is significantly raised from its resting level. The blue zone, meanwhile, is showing that you are at 60-69% of your maximal heart rate.
What kind of exercises would put you in the blue zone? You should only be in the blue zone during warm-up activities, recovery workouts, and long-duration, less intense workouts (power walking, hiking, etc.) You should not find yourself in the blue zone if you are doing intense weight lifting or cardio. If you are in the blue zone for these exercises, you probably aren’t working hard enough!
The benefits of the blue zone are that being in it can build vascularity (capillary beds supplying blood, oxygen, and nutrients to working muscles), increase mitochondrial density (fuel production capability), improve the ability to use fat as a fuel source. Again, this applies to relatively light workouts, warm-ups, and cool-downs.