Aerobic Deficiency is all too common among the people who approach Uphill Athlete for coaching and training. Don’t worry: Aerobic Deficiency Syndrome is not a fatal disorder. It’s a reversible condition we often see in those athletes that have spent too much time training in Zone 3 and above. These athletes often have finely-tuned anaerobic capacities from years of working out at higher intensities. They feel fit, fast, and strong, but their aerobic bases, and therefore their endurance,  are woefully underdeveloped—sometimes virtually nonexistent. Aerobic Deficiency is pretty much a given among the un-fit.

The Importance of the Aerobic Base

Sub-aerobic threshold work, what we call base training, is not event specific when it comes to shorter athletic events, such as a 5K or 10K running race or even a half marathon. You run those events at a high intensity—at or just above your Anaerobic Threshold—so your basic aerobic capacity plays a supporting role for the higher-intensity, event-specific work. In events shorter than about an hour, your performance is best predicted by your Anaerobic Threshold pace. You can think of this as your endurance limit—the fastest pace you can sustain for the duration of the event. If you were to pick up the pace even a tiny bit, you’d have to slow back down.

But if you’re training for an event over 3 to 4 hours in length, like a big alpine or mountaineering climb or an ultra-distance race, then the basic aerobic training is the event-specific training and the base training all rolled into one. That’s because the intensity you compete or climb at—your race pace or event-specific speed—is your Aerobic Threshold. In these longer events, your aerobic capacity is a direct measure of your event-specific endurance. You can’t spend too much time above your Aerobic Threshold in a long event, or you’ll blow up later and slow down significantly.

The Risks of Overdoing High-Intensity Training

At Uphill Athlete, we get a lot of individuals who have been training consistently above their event-specific pace, often at quite high intensities. They’ll go out for a 45-minute run and push as hard as they can, pegged right up against their endurance limit. Or maybe they’ve thrown themselves into high-intensity interval training (HIIT), where they rarely work out for longer than an hour and a half. That frenetic, pedal-to-the-metal approach doesn’t improve the aerobic base. In fact, it will have a deleterious effect on the base if done over a long period of time.

There is a time and a place for high-intensity training for endurance athletes. But high-intensity and low-intensity training cause very different endurance adaptations, and you need the right doses of each to maximally improve endurance. Overemphasizing the high-intensity work for too long will leave an athlete with Aerobic Deficiency Syndrome. Correcting this deficit will take months of a high volume of low-to-moderate-intensity work. There is no shortcut. So if you have been drinking the high-intensity Kool-Aid, you’d better be ready for the hangover it produces.

What Does Aerobic Deficiency Syndrome Look Like?

Your body adapts to whatever it does routinely. If you’re always training right at your endurance limit (Zone 3), your anaerobic and glycolytic metabolic system gets notably tuned up, which de-conditions the aerobic metabolic pathway. (It’s the aerobic pathway that primarily burns fat as fuel.) Another common adaptation is a reduction in aerobic enzyme concentration, because those enzymes are not getting enough aerobic training stimulus.

For people who have been on a steady diet of CrossFit or a similar HIIT-style program for even a year, their Aerobic Threshold may actually be at a walking pace. Their aerobic metabolism can’t produce any more power than this pace because they’ve left it untrained for so long.

Slowing Down to Get Back on Track

Patience is an important virtue when you have dug a huge hole in your aerobic base. When we inform an athlete with Aerobic Deficiency Syndrome that their aerobic capacity is in the basement and they need to train at that level, they oftentimes protest. “How can this possibly be doing anything?” they complain when we tell them they have to walk. “It’s too easy.”

Convincing people to take two steps back and slow way down is difficult. There’s this disconnect, this misconception that all training has to be done at a hard effort. These folks are accustomed to pushing the needle right up to their maximum sustainable pace, then holding it there as long as they can. In their minds, that’s training, and their muscles have grown really strong as a result. Now with their muscles no longer getting taxed to the same degree, they don’t feel like they’re training anymore.

A strong aerobic base is crucial to longevity in any endurance sport—and it is integral to long-duration activities, where it equates to the pace you will hold for the entirety of the event or objective. High-intensity training is a perfectly valid supplement to base training, when done on top of an already solid base. But it should never replace aerobic training. If it does, you’re on track for developing ADS. You may be able to run a 20-minute 5K or hike uphill for a couple miles at a faster clip than your friends, but that speed won’t translate into endurance over multiple hours or days. No one sprints up Everest.

To avoid or correct Aerobic Deficiency Syndrome, slow down. That’s how you’ll go longer, farther, higher.

-by Uphill Athlete co-founder Scott Johnston

Further Reading and Listening:

Interested in reading another viewpoint from another sport?

We recommend this article from VeloNews, the cycling website. They do a great job breaking down the why into understandable concepts. (Thanks to Uphill Athlete Bruno S for the link.)

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