During my evolution as a fitness coach, I geeked out hard on energy systems. In the world of CrossFit, the overwhelming trend was to go harder, faster, longer. The issue was that people began to burn out, get injured, or fail to sustain obnoxiously intense regimes. I quickly learned the value of a developing a solid aerobic base. It’s a key to longevity and one of the most time efficient methods to train the aerobic system is implementing aerobic interval training. But how do you know if one is primarily training that energy system?