Context:

Zone 2 cardio is not the singular key to building an aerobic base, and its popularity may outpace the evidence. A researcher critiques the reliance on proxies for zone 2 and argues that higher-intensity work often yields equal or greater adaptations in VO2 max and lactate threshold. With limited time, spending more effort above zone 2 can be more efficient for most people, and frequency matters—six sessions weekly can outperform fewer sessions. The takeaway is flexible: zone 2 is useful but not essential, and sustainable, time-efficient strategies that sometimes push beyond lactate threshold produce better or equivalent cardio benefits over time.

Dive Deeper:

• Zone 2 is defined as a very low steady-state blood lactate level, with some athletes using a lactate meter to stay below 2, while most rely on proxies like talk tests or heart-rate estimates; accuracy varies and many people train blind without lab equipment.

• Evidence shows higher-intensity exercise consistently enhances VO2 max and lactate threshold, whereas zone 2 alone did not outperform a control in a cited comparison across training modalities.

• The hype around zone 2 partly stems from observational data on elite athletes training 20–40 hours per week, where a large portion is in zone 2; experts caution that this does not translate to recreational schedules.

• There is no agreed definition of an 'aerobic base,' and literature supports including work above the lactate threshold to actually raise that ceiling rather than staying strictly below it.

• When time is scarce, integrating intervals or higher-intensity bouts provides meaningful gains; examples include 20-minute sessions with brief high-effort bouts and infinitely adaptable weekly plans.

• A meta-analysis cited suggests six training sessions per week yield better VO2 max improvements than four or two, independent of intensity or duration, underscoring frequency as a key lever.

• The interviewee personalizes training as flexible and sustainable, emphasizing variety over a rigid plan, and notes that her current approach adapts to pregnancy without claiming universal optimality.