Everyone has heard about the aerobic base. It is one of the most popular buzzwords in endurance coaching. But most athletes misunderstand what base training should actually include.
The Problem With Zone 2 Only Base Phases
Base training is usually defined as low intensity, high volume in the lead-up to a period of heavy race-specific work. And while low-intensity training is genuinely beneficial - it builds mitochondrial density, improves enzymatic efficiency, and enhances oxygen uptake in the muscle - doing weeks or months of exclusively zone 1 and zone 2 work is leaving performance on the table. This is one of the reasons 80/20 training may be holding you back.
Outside of injury rehabilitation, there is little reason to completely exclude high-intensity work from your base phase.
VO2 Max Is Also a Base
Your maximum oxygen uptake sets the ceiling for everything else. The higher your VO2 max, the more room you have below it for threshold work, sub-threshold efforts, and race-pace training.
Having a strong VO2 max already in place when you enter your race-specific phase means you can focus on efficiency at race pace rather than trying to build your aerobic ceiling during the season. This aligns with the principle that you should get fast before you go far. That is a far more productive use of your race-prep block. Keep in mind that the ceiling is only half the story: efficiency is what decides how much of that ceiling you can actually sustain in a long race.
How to Incorporate VO2 Max Into Your Base Phase
It does not need to be complicated. One VO2 max session per week, rotating through swim, bike, and run, is enough. Skip the high-intensity session during your recovery week.
In triathlon, the shortest race you will ever do is roughly an hour long - far outside the two-to-six-minute range where VO2 max is directly utilised. But that ceiling determines how sustainable everything below it feels. A higher ceiling means the same race pace requires a lower percentage of your maximum capacity.
Volume Does Not Need to Be Extreme
Base training does not require massive weekly hours. Whatever time you have available is enough. The priority is doing the right training to build the physiological foundations that support improvement in your specific event when race season arrives. In fact, your off-season should look similar to your in-season in terms of session types.
Low-intensity work provides the volume base. VO2 max work raises the ceiling. Together, they create a foundation that race-specific training can actually build on.
Speed is the base of endurance, not the other way around. Build your ceiling first, then learn to sustain effort below it.