Last week, I listened to an interesting interview with Iñigo San-Millán and wanted to share it with you.
Iñigo is the Head of Performance at UAE Team Emirates and a University of Colorado School of Medicine professor. San Millan’s research and clinical work focus on mitochondrial function, diabetes, cancer, and lactate metabolism.
Iñigo appeared on the Proof podcast with Simon Hill.
The science of zone 2 cardiovascular exercise (Part 1) | Iñigo San Millan, PhD
The podcast explores much of the science behind the health and performance benefits of Zone 2 training. Iñigo and Simon provide guidelines for structuring your Zone 2 training.
Here are a few of the things I found most interesting:
300 to 400 minutes a week of Zone 2. The CDC, the AHA, and the NHS recommend that adults engage in at least 150 minutes of moderate-intensity aerobic activity per week. For optimizing mitochondrial health, Iñigo recommends more than doubling that amount.
60 minutes minimum duration.
Iñigo believes that to stimulate an adaptive response properly, one needs to spend a minimum of 60 minutes in Zone 2.
Sixty minutes of accumulated duration is okay under certain conditions.
For example, training for 90 minutes and spending 15 minutes in higher intensities (Zone 3-5) may not subtract from your 60-minute minimum Zone 2.
However, ending your Zone 2 session with a high-intensity set may have less impact than putting it in the middle. Simon, the host of the Proof, agreed and admitted he does higher intensity work following his Zone 2.
Iñigo believes training at higher Zones will cause lactate to accumulate in the blood, which will take time to clear. Of course, it depends on the metabolic flexibility of the individual. Healthier individuals will clear lactate more quickly than less healthy ones.
The “talk test” is a good measure of intensity. Though Iñigo prefers and uses VO2/lactate tests to find training zones, he recommends the “talk test” over any formulas for calculating training zones. If you can carry on a conversation (though difficult) while exercising, you’re likely at the high end of your Zone 2.
All training requires oxygen and is therefore aerobic until Zone 6. Iñigo doesn’t like using “aerobic” and “anaerobic” to define training Zones. We now understand that all training Zones use oxygen except for Zone 6. Iñigo incorporates a Zone 6 in his program. Zone 6 is the point where energy production is truly anaerobic.
Zone 2 produces the most significant adaptation in mitochondria. But all Zones offer performance benefits. How much time you spend on each will depend on your performance goals.
Wearing a heart rate monitor during a weightlifting session, we will see Zone 2 level heart rates. Is this Zone 2? Iñigo’s answer was “no.” What you’re seeing is recovery from the effort. Zone 2 and the action of the mitochondria to burn fat as energy comes from sustained contractions from slow twitch muscle fibers. Weightlifting efforts use larger motor neurons and fast twitch fibers. Fat would not be the primary energy source.
80/20 rule for endurance athletes. Simon brought up the 80/20 rule for endurance athletes. The recommendation is that endurance athletes spend approximately 80% of their training in Zone 2 and 20% in higher Zones. In many of Iñigo’s articles, I’ve read that he prefers a 90/10 split for his athletes.
From a CrossFit perspective, I would flip the rule to 20/80 or even 10/90. And recommend that someone pursuing “fitness” give 10-20% of their training time to Zone 2 level efforts.
Giving 10-20% of training to Zone 2 won’t get you anywhere near Iñigo’s recommended 300 to 400 minutes a week of moderate intensity exercise.
As always, it comes down to what are you training for? What are your goals?