VO2max training involves higher-intensity anaerobic work. Now you are working beyond your lactate threshold to increase the maximal rate of oxygen transport (aerobic capacity or VO2max), build lactate tolerance, and increase anaerobic endurance. These workouts are at the opposite end of the continuum from the endurance workouts.
During this training phase, your key higher-intensity sessions consist of work intervals of 1-6 minutes in duration with a recovery interval equal to or slightly less than the work interval. For example, after you’re warmed up, you might do 4 x 3 minutes in the “uncomfortably hard” zone with 2 minutes easy recovery between. Total time at intensity for these workouts can range from 12-24 minutes.
For the “uncomfortably hard” VO2max intervals, you will need to breathe through your mouth. You may be able to say a single, short word, but only if you have to. Breathing rate is rapid with short, forceful breaths.
Aside from these key intensity workouts, the bulk of your training during this and any phase includes endurance workouts in the “conversational” zone and recovery workouts in the “easy” zone.
VO2max training might span 3-6 weeks in your training plan.