The lactic acid energy system uses glucose to create energy. Glucose is broken down during intense exercise, when the body cannot supply enough, oxygen to the muscles, producing lactic acid as a byproduct, lactic acid energy system also known. as the anaerobic energy system is one of the mechanisms are body uses to produce energy during exercise it kicks in when our body can't supply enough oxygen to our muscles for aerobic energy producing instead, this system rapidly breaks down glucose to produce energy by the buildup of lactic acid.