Module 7a: Aerobic Capacity

Ventilatory thresholds. | Module 7 - Aerobic Capacity and Anguish | Technical Essay

Aerobic capacity (AER) might be the most complicated, most misunderstood, and simultaneously most misused energy system to develop. In recent years, fitness trends and research love affairs have fluctuated between walking to rucking, Zone 2 to sprinting; each marginalizing fundamental steps along the way.

Photo by VO2 Master on Unsplash

As the anti-thesis to endurance (which seeks to answer “how far” or “how long”), aerobic capacity is the threshold of intensity where we seek to answer “how fast?” That is, we seek to increase our work capacity — the amount of work (calories, reps, watts, etc.) we can produce in an given time frame.

Mechanistically we can characterize this as:

• Oxygen update (VO2max)

• CO2 clearance (tolerance)

• Lactate clearance

• Blood pH (indicated by the above).

The National Academy of Sports Medicine (NASM) definition in their own publications for “metabolic conditioning” (METCON) itself is confusing; where “conditioning” is equated with “cardio.” In my opinion “conditioning” is a very broad term with a very specific application. Much like the term “fitness”, what task do I want to be fit for or stimulus do I want to be conditioned to?

On the other hand, is “cardio” short for “cardiovascular” or “cardio-respiratory?” Either would imply a specific set of organs to which we’re driving adaptation of. Can we train the vascular tissue without respiratory tissue? Well, tell me again what it is that is “pumped” during those previous hypertrophy sessions? Can we train respiratory tissue without improving vascular flow? Breathwork is an entirely different subject — that we’ll touch on later.

Recent training trends have both glorified “Zone 2” and tried to make “a case for never jogging again” while shilling the metabolic and hormonal benefits of sprinting. Meanwhile, the underlying premises are still being missed.

Where most people, myself included, go awry with endurance training is that they start at way to fast of a pace. In other words, what we think we’re training is endurance and Zone 2, but we’re really at a capacity / Zone 3 heart rate.

From there people tend to go one of two directions. They downshift to walking or rucking and miss Zone 1; or they try to redline to Zone 5 (alleged sprinting). The reason I say “alleged” is because the discipline cult and grind-mindset have us often adding too much volume to be useful here. As a result we’re either trying to drive with the emergency brake on, or never actually have the gumption to drop the hammer into a true Zone 5.

Never mind that along the way we also skipped the grueling and painful aerobic threshold work of Zone 3 that is precisely where aerobic capacity is developed.

On the other hand, when we skip Zone 1, we actually skip the vital foundation of our aerobic limitation. A casual stroll (< 50% MHR) isn’t stimulating enough to drive adaptation — though walking and general movement have a host of benefits overall. Rucking is okay, except adding load to your body weight tends to make overcompensation (e.g. in the back and hips) worse rather than better compared to the “forced march” or “airport / power walk” of a real Zone 1 focus.

Image Credit: Stages of Cycling

We can’t build a robust aerobic foundation on an upside down pyramid (e.g. always focusing on and trying to add more high intensity work) any more than we can expect a lemon to stand up right (e.g. always focusing on the middle zones).

In the long run this “regression to the mean” is detrimental because our training is neither easy enough to promote recovery, nor hard enough to drive novel adaptation. Sessions only “feel” hard (hence the misappropriation of RPE) but our objective performance becomes incongruent from our applied effort. This is a classic example of “overtraining” being much more a case of “under recovery.”

For all the hubbub about “metabolic flexibility” from a dietary perspective, its very interesting to consider that ventilation may be a much more indicator and primary signal to fuel substrate turnover than dietary inputs. In other words, respiratory changes create changes in blood and brain chemistry much faster than dietary ones like macronutrient ratios.

Alan Couzens suggested a benchmark test of running 1 mile in 11 minutes (about a 5.5 mph pace) without exceeding 70% MHR. Similarly, Brian Mackenzie has suggested 20 minute on a Bike Erg about about 20 nasal breaths per minute and maintaining the same HR threshold. If you can’t do either of these, you’re not aerobically fit and not metabolically flexible — your ventilatory in/efficiency will dictate fuel substrate accordingly.