I'm writing you today post-VO₂max run, before my work shift starts with a sick dog to my left and a coffee to my right. We're taking it easy this morning while I think some more about aerobic training, and as I try to get back on track after missing a few newsletters while I got the *new* clinic/gym set up!

Here's what's on my mind: yesterday I posted THIS reel about Tabata training and got a question from a client that made me pause:

It reminded me that a lot of people are looking at the VO₂max number their watch spits out and assuming it’s accurate, useful, and actionable. Here’s the reality:

1. It’s a guess. Smartwatches use algorithms that estimate VO₂max based on your heart rate and pace during certain types of runs. Multiple studies have shown that these estimates can be way off - sometimes by 5–15%, especially if you don’t run regularly in the “right” conditions the watch needs for its calculations.
2. It tells you nothing about pace or power at VO₂max. A lab or field test gives you this - which is critical for programming high-intensity work. Without it, that “57” on your watch doesn’t help you target the right speeds or outputs in training.
3. Heart rate alone is not something we use to tailor your high intensity training. Your HR can drift for reasons unrelated to oxygen uptake (heat, dehydration, fatigue, low carb availability). This is why HR zones are best for submax training, while pace, power, or RPE are better for high-intensity intervals.

The studies I’ve linked below (Burnley et al., Stöggl & Sperlich, and others) make two things clear:

1. VO₂max is trainable, but not by hammering VO₂max intervals all the time. VOLUME of training tends to produce the largest gains, and if your volume box is checked ✅, then worrying about Polarized training is the next box to check ✅ (about 80% easy, 20% hard), rather than endless “middle” intensity or "junk zone" training.
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2. The “hard” 20% is specific. VO₂max intervals are typically 3-5 minutes at an intensity you could only sustain for ~6 minutes, with equal or slightly shorter recoveries. This is not the same as sprinting all-out for 30 seconds or cruising at a steady “comfortably hard” pace.

Consistency trumps short-term heroics. Improvements in VO₂max take weeks to months, and gains are much more about steady aerobic development than smashing one “killer” workout.

(If you want help structuring your training to build VO₂max while staying healthy, our Basic Endurance Coaching program is on sale right now for only $80/month (regular $110). Perfect if you want a personalized plan without weekly check-ins, and it includes group calls to guide you through the process.

Now if I still have your attention, let's talk about WHY VO₂max matters.... not just for athletes. Sure, for athletes, VO₂max is a key performance metric - it reflects your maximal aerobic capacity and correlates with endurance potential. But for the general population, VO₂max is one of the strongest predictors of overall health and longevity.

Low VO₂max is linked to higher risk of cardiovascular disease, metabolic disorders, and even all-cause mortality.

Improving VO₂max through regular aerobic training can lower blood pressure, improve insulin sensitivity, and enhance your body’s ability to recover from stress.

See attached chart for “good” VO₂max scores by age and sex so you can see where you stand:

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So the takeaway is that knowing your estimated VO₂max is like knowing the “miles per gallon” number from a car ad - interesting, but not necessarily what you’ll get in real life.

If you actually want to train at the right intensities, you need either:

• A maximal VO₂max test in the lab (gold standard)
• A validated sub-maximal test, tailored to your sport.

That way, you get both your real VO₂max and the training speeds or powers that match it.

Coming soon in Calgary (for the first time since COVID put a damper on our testing services), we’ll be re-opening VO₂max testing this fall. If you want to get your actual number (and more importantly, the training zones that go with it), reply to this email and we’ll send you details before bookings open.

Further reading & listening:

​Burnley et al., 2022 - Polarized Training is not optimal for Endurance Athletes​

​Stöggl & Sperlich, 2014 - Endurance Training Intensity Distribution​

​Tabata et al., 1996 - Intermittent vs Steady-State Training​

​Accuracy of Wearable Devices in VO₂max Estimation​

​Accuracy of Apple Watch in VO₂max Estimation​

​Peter Attia Podcast on VO₂max & Longevity​

Yours in physiology,

Carla