In the last few years the expression ‘energy systems’ has come into general use in the climbing world to describe the various ways the body creates and uses energy. Along with it, however, has come a rather bewildering collection of sub divisions (aerobic threshold, anaerobic power, aerobic capacity etc). The differences between these various categories have been explained by several commentators yet often, in my experience, those explanations have left people more confused than before! The following is an attempt to make this complex subject as simple as possible. With a little bit of study it will be seen that a clear understanding of the various elements that make up ‘energy systems’ will help any climber to train more effectively and efficiently.

There are two types of energy system: Aerobic and Anaerobic.

(1). Aerobic Energy System

This system uses fats or carbohydrates plus oxygen to fuel the synthesis of ATP which fires muscles; the beauty of this system is that no waste products are created. The more developed the system is the more able you are to do work ie. Exercise without stopping. Via training a climber is able to develop their aerobic system (or Aerobic Base) so that they are able to increase the percentage of their VO2 max (the maximum amount of oxygen that one’s body can process and sustain for several minutes) for long durations (over 30 minutes) of exercise. The enzymes in the muscle cells (mitochondria) that help create ATP are key and the more of them there are the fitter the climber will be. More and faster work can be done ie. endurance and speed of movement will increase via the correct training. However, the muscle fibres that are used for such work (slow twitch or ST fibres) have limits to the intensity of work that they can perform. At a certain point of intensity the body will start to change the energy system it uses and operate increasingly via anaerobic energy. There is a certain amount of crossover here as the body begins to use a hybrid muscle fibre called Fast Twitch A (FTA). These fibres are larger in diameter than ST fibres and more powerful and initially use aerobic energy as their fuel source. Soon, however, they become mainly glycogen ie anaerobically, fuelled. They can be converted into ST fibres (or at least given some fatigue resistance) by training.

 When the body is operating at a very high intensity (90-95% of maximum heart rate) the metabolism switches to purely anaerobic; this point is called the Anaerobic Threshold.

(2). Anaerobic Energy System

This uses glycogen as a fuel and does not need oxygen. It provides ATP quickly and is much more powerful than aerobic energy. The pure Fast Twitch fibres (FT) that are used are very strong but have little fatigue resistance. They require real mental effort to be stimulated due to the high electrical threshold needed to fire them so a highly developed nervous system is required to maximise their efficiency. The big problem with this system is that production of ATP from glycogen (glycolysis) creates lactate as a by product. For a while the body can remove this by product to be used as a fuel elsewhere in the body-this process is called the Lactate Shuttle. Eventually though, the body’s ability to do this reaches a limit and lactate levels rise very quickly as the H+ ions created by glycolysis increase acidity in the body leading to extreme fatigue ie. “I’m totally pumped!”

This, very roughly, is the general situation but how to improve the operation of these energy systems in the most effective way? A route climber will see from the above that both the Aerobic and Anaerobic systems are required on any route near/at/beyond the climbers limit. A debate rages over the merits or otherwise of various training programmes but, before descending into the twilight world of what exercise when, the following may be of value.

No matter how strong a climber (pure  Anaerobic Power) they are, on routes, at the mercy of the Lactate Shuttle ie. If they have a poorly developed lactate Shuttle they will pump out quickly when the climbing gets intense. Although FT fibres give high muscle power outputs the length of time that you can sustain that output for is dependent on the Aerobic Capacity (AeroCap) of ST fibres as it is the AeroCap that improves the shuttles ability not the FT fibres.( Nb. The AeroCap is the combination of one’s VO2 max and the percentage of your maximum strength you are capable of for long durations. Whilst VO2 is difficult to improve the second element is very trainable).

In other words, AeroCap is extremely important for high exertion climbing; whilst high and super high intensity training is important to improve the capacity of the nervous system to work as effectively as possible when anaerobic energy is being used, overtraining in this area leads to a drop in aerobic fitness. It is, therefore, important to raise and maintain the Aerobic Threshold (AeT) to as high a level as possible (the AeT is the point where blood/lactate levels first rise above normal). If this is done it is then easier to raise the Anaerobic  Threshold ie. raise the level where the Lactate Shuttle becomes overloaded, and slow down the onset of ‘pumping out’.

A high volume of low intensity training at/below the AeT is essential to start raising the shuttles level then, by progressively increasing the volume of training at moderate intensity the shuttles effectiveness is further increased. In so doing the Aerobic Power of ST fibres and the AeroCap of FT fibres increases. The ‘at/below’ AeT training is essential to maximise the process, there are no shortcuts!

As you can see (I hope!), there is a tricky juggling act to be performed. However, whilst all climbs are different and require different balances of aerobic and anaerobic abilities it seems clear that, if you were new to climbing the main focus initially would be on developing the Aerobic Base (ie. raising the AeT). Many more experienced climbers may not want to go back to basics but it does seem that this is the most sensible course of action to take. For newcomers or those who tend to climb more than train a useful training plan is easier to create as improvement in all areas is so much easier to achieve! A simple way to focus indoor (or even outdoor) climbing time into something of long term benefit is to divide up that time by a simple ratio method. 5:4:1  equates to 50% of ones climbing time being devoted to easy routes, roughly 60% of your maximum onsight level but making sure that you do a lot of them! 40% of your time is spent on quite high intensity routes ( 90-100% of your maximum onsight level) and 10% bouldering, campussing etc. This is a very rough outline but is simple to follow and helps build up your Aerobic base as discussed before.

For climbers who have been pushing their limit for a long time the situation is more complicated and it is here that a lot of research, self analysis and/or a good coach are important. At this level the balance between low/medium intensity and high intensity training becomes critical in reaching ones maximum potential and requires a very carefully structured training plan. At a certain point in any climbers career a ceiling will be hit beyond which it is hard to progress. The answers are out there, it’s just a case of how determined you are. Good luck!


The above is obviously based on the work of others-I am no sports scientist! There is a mind boggling amount of literature out there but be warned, once you start its hard to stop!

The simplest guide I found and the most related to climbing was:

Training for the New Alpinism   A Manual for the Climber as Athlete   S.House  S.Johnson Patagonia Books 2014  Chapters 2&3 are particularly relevant though the whole book is invaluable!

For the keen the following are a taste of what’s out there:

Periodisation Training for Sports 2nd ED.  Tudor O. Bompa & Michael C. Carrera   Human Kinetics 2005

Science of Sports Training: How to Plan and Control Training for Peak Performance  2nd Ed.  Thomas  Kurz   Stadion Publishing 2001

“The Lactate Shuttle During Exercise and Recovery”  Brooks 1986  Medicine and Science in Sports and Exercise 18(3) 360-68

“Skeletal Muscle, Mitochondria and Myoglobin, Endurance and Intensity of Training   Journal of applied Physiology 54(3): 798-802






Back to Blog
Share this post