Many are familiar with the concept of periodization as it applies to training. For example, you cannot always be pushing heavier weights, there needs to be phases (micro cycles) where you emphasize hypertrophy, deloads, and using other methodologies to ensure progression and to reduce the chance that of your body adapting to the training stimulus. This concept of adapting is most often noted by those that favor metabolic (cardio) based conditioning. Over time the body will become more efficient at running on the treadmill. As efficiency is gained, the net caloric loss or energy expenditure is reduced. This adaptation can stall fat loss if not taken into consideration.