This is a quick overview of the human body’s energy systems (metabolic pathways) as they relate to rock climbing. Most of the information herein is taken from a Power Company Climbing podcast, Energy Systems Training with Eric Horst. There are also bits taken from an earlier podcast from Power Company, Deadlifting with Steve Bechtel which also has great all around training suggestions.

Also, for the purposes herein I refer to strength and power synonymously in regard to maximum recruitment. Remember, power is just strength divided by time (maybe the a discussion of the benefits of each will come in the future).

Anaerobic - Alactic:

Fuel Source: ATP-CP

This energy system is responsible for short actions of the highest intensity. Maximal output with this system lasts about 10 seconds. So, a short, hard boulder, or the crux sequence of a route, or a weighted deadhang.

Noted rest:work ratios here are anywhere from 10:1 to 20:1. That means up to 3.5 minutes of rest for every 10 seconds of work. If you’re feeling pumped, you’ve stopped training strength and have begun working endurance. Consider using stopwatch or your smartphone to time your rests and make sure you’re getting enough between sets to truly give a maximal effort on the next go. If you have to ask yourself if you’re ready to really try hard again, you’re probably not.

The other energy systems may leave DOMS (Delayed Onset Muscle Soreness, but as far as this system relates to climbing, it’s far more taxing to connective tissues than muscles which tend to not tell you they’re on the fringe until it’s too late (i.e. little warning before a tendon “pops”). This training can also be very taxing on the central nervous system which doesn’t give as clear indicators as sore muscles either (see below link on Maximum Recruitment and this one from LiveStrong).

Anaerobic - Lactic:

Fuel Source: Glycogen (blood sugar)

This is the system associated with what’s commonly called “strength endurance”. Horst states that this system is the most difficult to train, but it seems to that that is simply because it is the fastest to detrain / regress. Ironically, it’s also the fastest to progress and see gains in.

It’s is also sometimes mentioned that this system is a function of the others. So, you my see benefits in the middle ground by training the extremes.

Rhis system has an upper limit of about 2 minutes. In climbing terms, that means 2 minutes to finish a long boulder or find a rest on a route.

More good information in the podcast comes from discussions about lactate. That is, “lactic acid” isn’t really a thing. Lactate is and Hydrogen ions are. This was news to me as I hadn’t really distinguished between “lactic acid build up” and DOMS; which I know now are not the same thing. Lactate isn’t bad, in fact, it fuels ATP production. However, the Hydrogen ions are bad as they cause a drop in your body’s PH level – making it more acidic. Hence the burning pump.

There is great term referenced in the podcast – “pump lust.” Not just climbers, but everybody (myself included) wants to “feel like they worked hard”, but there’s a difference between training with a purpose and doing something just to feel tired / sweaty.


Fuel Source: Oxygen (and fat)

This energy system is used for intervals over 2 minutes. It can take you up to several hours, but Horst recommends 10 minute intervals. The rationale is simple, the system needs to be taxed enough to force adaptation. So, how much capacity / work can you fit in to that 10 minute window. The numbers cited in the podcast are somewhere between 70% and 85% of your max. So, if you climb V10 that’s continuous V7/8 climbing.

With that information, the goal is a “controlled pump” rather than a “blistering, I’m about to fall” pump. You should notice that it’s taking some effort to maintain, but you’re not getting “winded.” If you’re thinking ARC training then you’re right on, but remember it should take effort (significantly more than half) and not be a lollygagging jug haul.

Putting Things Together:

Energy System Duration Fuel Source Training
Anaerobic Alactic < 10 seconds ATP-CP Weighted hangs, 5 move maxes, campus max
Anaerobic Lactic < 2 minutes Glycogen Hangboard repeaters, 4x4s, campus ladders
Aerobic > 2 minutes Oxygen ARC, > 2 min intervals

“All recovery is aerobic.” General aerobic conditioning helps regenerate the fuel (ATP and CP) required for the Anaerobic Alactic system.

The stronger you are, the higher your “try hard” threshold is for elongated Anaerobic Lactic tasks (e.g. 4x4s). What’s the average grade of the last 4x4 you did? How “hard” would the same problems feel if your highpoint was 2 grade higher?

Similarly, the more total recruitment (strength) you can generate on any given move, the more your perception changes about what constitutes a “rest hold” on an Aerobic task. The example in the podcast is a 5.14d climber on a 5.12a route thinking every hold is a jug.


Horst talks about a more traditional block peridization, which you can read more about in pretty much all of his books. But other perspectives do exist. Personally, I’m critical of the exclusion of traditional block periodization which seems most applicable when gearing up for a trip, or when you only get one good season per year.

I’m much more fond of Bechtel’s approach to “boil” one aspect while you “simmer” the other two. This is still periodization. But it’s an attempt to not regress during different periods of focus. Of course you’re route and boulder seasons have different focuses, but how great would it be to not have to spend the first month of each trying to make up lost ground?! The idea is to push hard in one domain while maintaining the others. However, that while you can train different systems within the same week, only the most elite in the world can train multiple systems (effectively) in the same day.

Steve Bechtel thinks the flatline for most people in a given facet seems to happen around 6 weeks with the lower end being about 4 weeks. That sounds right based on my experience. Steve has a good point that 4-week cycles are very convenient for how we schedule our lives, but I’m hesitant to pass judgment on any training routine I haven’t given a solid and consistent try for at least 4 weeks. So 6 weeks of training usually calls for reassessment and either a change of direction (boil a different facet) or method of stimulus.

The more I hear the concept, the more truth I think there is to it: Progress “doesn’t come fromw what you did in the last 10 days, but the last 10 weeks, or 10 years.”

Additional Resources:

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