By Uphill Athlete co-founder Scott Johnston
Aerobic Deficiency Syndrome (ADS) is all-too-common among the people who approach Uphill Athlete for coaching and training. Don’t worry: it’s not a fatal disorder. It’s a reversible condition that results from doing too much training in Zone 3 and above. People who exhibit it often have fine-tuned upper ends (anaerobic capacities) from years of working out at higher intensities. They feel fit, fast, and strong, but their aerobic bases are woefully underdeveloped—sometimes virtually nonexistent.
Sub-aerobic threshold work, what we call the base, is not event-specific training for shorter athletic events like a 5 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 the role supporting 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 start significantly slowing down.
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). They rarely work for longer than an hour and a half. That frenetic, pedal-to-the-metal approach doesn’t improve the aerobic base, and in fact it has a deleterious effect on the base if done over a long period of time.
There is a good case to be made for including some 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 ADS. 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.
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 deconditions the aerobic metabolic pathway; this pathway primarily burns fat as fuel. Another adaptation is the reduction in aerobic enzyme concentration because they are not getting enough aerobic training stimulus.
For people who’ve 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 equivalent to this pace because they’ve left it untrained for so long. When these people find out their aerobic capacity is in the basement and we tell them they need to train at that level, they don’t feel like they’re training anymore. “How can this possibly be doing anything?” they complain. “It’s too easy.” Their muscles are really strong from doing all that high-intensity work, and now that they have to walk, their muscles aren’t getting taxed to the same degree. Patience is an important virtue when you have dug a huge hole in your aerobic base.
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 the maximum sustainable pace, then holding it there as long as they can. In their minds, that’s training.
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, so slow it down to go farther and higher.
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.)