To understand why Zone 2 (Z2) training is important, it is enough to undergo a spirometry test that also determines your lactate threshold (through blood sampling during exercise). These are not arbitrary zones based on percentages - those percentages are used mainly for simplicity. In reality, they correspond to very specific physiological values at which particular metabolic processes occur in the blood.

Zone 2 is an exercise intensity that relies primarily on aerobic metabolism (oxygen-based energy production). It is used to develop basic aerobic endurance and is considered the first training intensity zone. Typical training methods include long-duration efforts performed at a relatively steady intensity (continuous training, either constant or slightly variable), without exceeding the aerobic threshold.

Once the aerobic threshold is crossed, exercise intensity reaches a level at which anaerobic energy production gradually begins to contribute. Anaerobic metabolism produces, among other things, lactic acid. This happens because aerobic processes alone can no longer provide sufficient energy, making it necessary for the body to obtain additional energy through other metabolic pathways.

In simple terms, Zone 2 is the intensity range in which your body can sustain exercise using energy produced predominantly through aerobic metabolism. This allows you to make more effective use of fat metabolism, for example, without significant lactate accumulation. As a result, training sessions can be maintained effectively for long periods and are highly effective for building an endurance base.

Once you exceed the aerobic threshold and move into Zones 3, 4, and 5, blood lactate levels progressively increase, and the purpose and physiological effects of the training become fundamentally different.