Third Gear: The Aerobic Energy System

by Steve Bechtel

A few years back, I was asked during an interview how important running is to climbing performance. Somewhat reactively, I said, “Running is as important for climbing as climbing is for running.” Over the years, I’ve received more than a fair number of messages and emails about this statement. Although there are some exceptions, I stand firmly behind this sentiment. 

One of the truths of training is that your body adapts very specifically to the demands put on it. The reason many of us take up running is because we feel our “cardio” is lacking in hard climbing efforts – since we find ourselves sucking wind as we work through the crux section near the anchors. The problem with “Me breathe hard when climbing and me breathe hard when running so both are the same” is that cardiorespiratory fitness developed by low-intensity activity like running is not the issue in climbing. In climbing, uptake of oxygen is not difficult, it is the delivery of fuel to the muscles, and the mechanical difficulty of breathing with most of your muscles contracted while trying to hold onto the wall. 

Climbing is not a cyclic steady-state activity. Climbing is an acyclic anaerobic-aerobic activity. So never run, right?

Well… the truth is that anything you do that lasts more than a couple of minutes is primarily aerobically fueled. As we dive deeper into the methods of developing aerobic fitness for climbing, we’ll see that there’s a place for general aerobic training in developing cardiac output, but that we then need to hone that conditioning with more specific exercises. 

We build aerobic fitness by using aerobic pathways. Although you might hear some buzz about super-high intensity training having some profound effect on the cardiovascular fitness, this is very limited in nature and tends not to be a great overall endurance modality. 

In short, the longer your effort (or day in the mountains) the more important aerobic endurance becomes.

Aerobic Energy Production 

The aerobic system is the primary energy system we use for long efforts of exercise…and for being alive. The system uses fat as a fuel source, as well as sugars, and ends up providing around 90% of our daily energy. This fabulous system can literally fuel your movement for as long as you can stay awake in a day, yet this great capacity comes at a cost. The aerobic system’s endurance comes at the cost of power. 

The aerobic system is 100% dependent on having sufficient oxygen supply. If enough oxygen is not available, the body begins to use anaerobic energy sources, and endurance drops precipitously. 

Although there are many steps in the production of energy aerobically, this pathway is limited only by substrate (carbohydrate and fat) availability, oxygen utilization in the muscles, oxygen supply to the blood, and aerobic enzymes. Improving these four areas is what we do when we train for greater aerobic capability. 

Aerobic Power

When we go climbing on long and step routes or when we hammer through a 3-hour bouldering competition, we can feel the pump in our forearms and the general fatigue that sets in. Even though we are generating a lot of energy anaerobically in these situations, it is important to understand that the majority of energy still comes to us aerobically. Additionally, remember that all recovery from anaerobic training is achieved via aerobic modes. 

It follows, then, that if our aerobic fitness is poor, both our anaerobic output and our recovery from anaerobic efforts will also be poor. This has been a major revelation in my coaching over the past few years. Although deeply interested in improving sport-specific conditioning, I was dismissive of the tremendous potential of the aerobic system. 

If we train for aerobic power, and eventually increase overall energy production via this pathway, we will see a significant decline in reliance on anaerobic energy stores. An increase in pulling power from the aerobic system effectively moves the anaerobic threshold (the point at which our bodies switch to primarily anaerobic energy sources instead of aerobic ones) up. The anaerobic threshold moves closer and closer to your maximum heart rate the more aerobically fit you become. 

With greater aerobic power production, it follows that at any given heart rate, power production increases. In the real world, this means that after improving your aerobic power, a route at a given level can be done at a lower heart rate (energy cost) than before, or a harder route can now be done at the same heart rate as a slightly easier one did. In the realm of pure endurance climbing, this is a major gain. On routes where fatigue is the major limiter, I suspect you can improve 1-2 grades just by improving aerobic power. 

System Adaptations to Aerobic Training

A common misconception is that aerobic fitness = “cardio.” It is not just cardiovascular endurance and it is not just about improving the cardiac and pulmonary interaction. As important as improving these factors might be, in most sports (climbing included) specific development of the muscles is just as important. 

To improve aerobic energy production you need to do one (or more) of the following three things:

1. Increase the supply of oxygen to the working muscles. This happens by improving cardiac output, by expanding the peripheral vascular (blood) network, or by improving respiration.
2. Increase the amount of oxygen the muscles can use. This occurs by improving the availability and number of aerobic enzymes, by improving the ability of fast twitch (high power) fibers to use oxygen, and by increasing the size and number of slow twitch (high endurance) fibers.
3. Increase the substrate availability for aerobic energy production. This includes improving the efficiency of the aerobic energy production, increasing storage capacity of substrates in the body, and hormonal regulation.

Once again, we revisit an energy system’s power and capacity. The first two categories above are improved by training aerobic power. Training capacity, we can improve some of the factors in oxygen utilization, and see big increases in substrate availability. 

We can improve the endurance of all the muscle fiber types, and contrary to popular belief, can do so without a significant loss in power if training is done right. Through training intelligently, we can increase the mitochondria (aerobic power plants inside cells) and aerobic enzymes. We can also train the body to increase fat and carbohydrate storage, which is essential for big days and long routes. 

Training the Aerobic System

“Many trainers and coaches in start-and-stop sports believe they have to train more in the anaerobic systems to improve that metabolic quality within the sport. It is possible to get so focused on repeated sprinting and intervals that athletes do not develop the aerobic engine to sustain that kind of training.” – Darcy Norman, High Performance Training for Sports

Training the aerobic system, as I have said earlier, is more nuanced than just getting your heart rate up and starting to sweat. Aerobic fitness comes both from increasing the power and the capacity of the system. 

The primary type of nonspecific session you’ll want to use will be a cardiac output session. These long, slow efforts are typically sustained exercise for 30+ minutes at (for most athletes) a heart rate of 120-150 beats per minute. Early in your training phase, nonspecific modes are fine, such as running, cycling, or uphill walking. Better methods would be exercises that involved the upper body, such as rowing, cross-country skiing, air bike, or swimming. As the season progresses, sustained extensive endurance (sometimes referred to as ARC) climbing, weight circuits, or combinations of climbing and non-specific exercise can be implemented effectively. 

The goal of cardiac output training is to increase the stroke volume of the heart, which leads to lower working heart rates, and higher cardiac efficiency. Higher intensity modes (such as HIIT training or Tabata intervals) lead to concentric hypertrophy of the heart, which can lead to a reduced heart volume (the heart chambers contract before full, thus no eccentric overload).

The aerobic system can also be trained via a variety of intervals, tempo weight training, anaerobic threshold training, or explosive repeats. 

Training Aerobic Capacity

In a performance sense, aerobic capacity is the ability to climb continuously without getting fatigued. Through proper training, your athlete will be able to do climbs of greater sustained difficulty fueled by the aerobic system. This means being able to execute a greater percentage of each climb without noticeable fatigue. This manifests in the ability to climb longer sections without resting and also in the ability to recover more quickly on rests as well as between routes. 

In endurance sports, athletes are monitored via heart rate or power output to assure they are maximizing the aerobic system. We don’t use our aerobic system to near the degree that a runner or cyclist might. The aerobic capacity climbers are addressing is more in terms of local muscular endurance. At this time, sport science doesn’t have a great way of monitoring climbers to help them stay in the aerobic capacity zone. Here are a few guidelines to help you hold the proper zone:

1. Climbing should be somewhat continuous in nature, with few long pauses or rest, and should be done on technical terrain. If climbing movement is too easy, the muscles will not develop properly. 
2. Climbers should have an elevated breathing rate, but not to the point that it is labored. Nasal-only breathing is an excellent way of assuring intensity stays low.
3. A second measure of proper intensity is the “talk test.” If you can speak in full sentences without gasping for air, the intensity is sufficiently low.
4. There should be no forearm pump. For some climbers, this intensity for any duration over a couple of minutes, will have to be very easy at first. 
5. In general endurance training, such as hiking or using cardio equipment, you can monitor heart rate. Aerobic capacity is best developed near the aerobic threshold, which can be roughly estimated at a heart rate of 180 – age. This heart rate zone should be monitored in conjunction with breathing or with conversational intensity. 

Aerobic capacity sessions will normally be driven by duration. As a general rule, you should look for continuous aerobic activity of at least 20 minutes and as high as 90. These periods can be split up with rests within a workout, but an aim toward completing the total duration is the key to adaptation. Over time, your program should ask that you do more total work and potentially increase the duration of individual sets. 

Cardiac Output 

We all know about “cardio” and its overall benefits to health. We also know that our bodies show some of the same responses to hard climbing as they show to difficult cardiovascular training, such as sweating, fatigue, increased heart rate, and labored breathing. The idea of doing more of this to get better at that is not a tough connection for most climbers to consider, yet we have to be cautious. Simply adding in several hours of running or cycling per week to your plan will not magically increase your ability to avoid getting pumped.

Although using cyclic endurance exercises (running, cycling) to build climbing endurance is not recommended, Cardiac Output training has its place in your conditioning program. The cardiac output modes can be just about anything that increases the heart rate and is sustainable for 20-90 minutes, but a few guidelines should be followed. By holding the intensity fairly low, your adaptations differ from harder interval-style efforts. Long, slow training increases the stroke volume of the heart, which results in eccentric cardiac hypertrophy. This, in turn, improves cardiac efficiency, decreases resting heart rate, and decreases working heart rates at any given level of work. Higher intensity exercise (tempo-paced efforts or exercising close to anaerobic threshold) result in concentric hypertrophy – and instead of increasing stroke volume will increase the heart’s ability to exert more pressure…essentially by increasing heart wall thickness and size. You don’t need this high level of cardiac development for climbing.

If we plan interval-style efforts, we train the heart to contract quickly, often before the chambers fill completely with blood. This doesn’t allow for the eccentric overload we are looking for. What we need is lots of slow, steady activity, preferably using the whole body. 

For Cardiac Output sessions, follow these guidelines:

• Plan them 1-3x per week. If you are challenged by these efforts, more frequent and shorter sessions are the key. These can be done on the same day as other training if desired. 
• Program exercise for 20-90 minutes in as close to a non-stop mode as possible. 
• Cross-country skiing, swimming, rowing, or machine training that requires both upper and lower body involvement (SkiErg, air bike, rowing machine) are the best. Hiking or easy jogging are OK. 
• Maintain conversational intensity (being able to speak in full sentences), or a heart rate of 120-150 beats per minute. 
• Increase the training effect by adding more sessions or longer durations – not by increasing speed.

Continuous Climbing at Low Intensity

This workout is a staple of endurance training. In a climbing gym or bouldering area, you should either do multiple laps on a route or combination of routes that allows for continual, steady difficulty. You can also do this in a bouldering gym that has plenty of holds and easy problems. At the crag, a toprope or two on adjacent routes should suffice. Following the same general guidelines as Cardiac Output, most climbers should aim for 10-30 minutes of nearly continuous climbing. Up and downclimbing is good, but climbing up and quickly lowering then immediately starting again works as well. 

The key is to build volume of climbing over the course of several weeks of training, and build up the time of each climbing set. It is probably not necessary to climb longer than about 20 minutes per set at first. 

For Continuous Climbing sessions, follow these guidelines:

• Train 2-3x per week. If you are challenged by these efforts, more frequent and shorter sessions are the key. These can be done on the same day as other training if desired. 
• Program exercise for 20-90 minutes in as close to a non-stop mode as possible. When climbing with a partner, 20 minute sets alternated between partners is fine. 
• Toprope laps, bouldering traverses, or combos of routes are good. 
• Climbers should maintain conversational intensity (being able to speak in full sentences), or a heart rate of 120-150 beats per minute. Be sure you avoid developing a pump. 
• Increase the training effect by adding more sessions or longer durations – not by increasing difficulty of climbing.

Route 4x4s

This is a good partner session or session for teams. Each climber picks a sufficiently easy and sustained route, leads it, then topropes it 3 more times with no rest other than a quick lower-off. After these 4 laps, you get to rest and belay your partner for roughly the same amount of time. You then repeat this for 3 more times on routes of similar difficulty, getting a total of 16 climbs in. You should not get super pumped, but just feel warm. If you go through the whole thing easily, up the grades slightly, but don’t reduce rest or add sets. Far more often, climbers err on going too hard and end up not completing the session in the right energy system.

For Route 4×4 sessions, follow these guidelines:

• Plan in conjunction with other Aerobic Capacity modes, 1-2x per week. Can be combined with weight training days or with Cardiac Output sessions.
• Climbers should start at approximately 4-6 grades below onsight level, and pay close attention to staying near aerobic threshold by paying attention to breathing through the nose or doing the talk test.
• Toprope laps or lead + 3 topropes are fine. Hard to do in a bouldering situation. Can be done on a treadwall.
• Climbers should maintain conversational intensity (being able to speak in full sentences), or a heart rate of 120-150 beats per minute. Be sure your athletes avoid developing a pump. 
• Increase the training effect by increasing the difficulty of the routes or by adding another set of 4 to the end of the session. 

Training Aerobic Power

Aerobic Power is what most of us call power endurance or resistant climbing. In a real-world setting, it is a sustained effort of climbing that is relatively difficult with no good rests that results in a large amount of accumulated fatigue. Maximizing this zone has to do with being strong enough that holding on is not an issue, having enough bouldering power that the moves don’t require big anaerobic efforts, and having a high aerobic capacity. Once your check all these boxes, aerobic power can be maximized. 

Aerobic power sessions are built around handling being very pumped, where your capacity sessions were all about building the systems to avoid it. I can’t overstate the importance of spending most of your endurance training time working on putting out less total energy per pitch (via improved movement, increased aerobic capacity, and staying calm) instead of always chasing aerobic power. Don’t forget it. 

In general, the sessions you do should feature very sustained sets of climbing that force you to keep going, rather than having cruxes that shut you down or rests that give you something back. Instead of progressing the sessions by adding more and more volume as you might in a capacity session, you can advance aerobic power sessions by reducing rest between sets. 

Boulder 4x4s

This is a staple of hard power endurance training, and is especially attractive to climbers with a densely set wall or a bouldering-only gym. The beauty of this session is in its simple structure and its near-immediate feedback that you have done something hard. Work on good movement, focused breathing, and progress across a series of several sessions. 

To start, pick 2-4 problems that are slightly below your onsight level. You will do four problems, either a combo of doing one problem four times, alternating between two problems, or doing four separate problems. You climb these back-to-back with no rest, then rest for a fixed amount of time. Somewhere in the realm of a 1:1 work to rest ratio is a good start, so 3-4 minutes is usually prescribed. 

You then repeat the same effort three more times at the same level of difficulty, always taking that same 3-4 minutes of rest between groups of four problems. If performance really declines in the latter part of the session, reduce the overall difficulty of the problems.

This session is normally combined with other training, such as being tagged on to the end of some hard bouldering. If it’s done on its own, you can program two or even three full series (32 or 48 total problems), with 15-20 minute rests between series. 

Campus Foot-On Ladders

Boring but effective. This workout is done on a Campus Board with foot rails. The idea is to do a fixed amount of simple laddering – don’t worry about getting fancy here – to destroy the forearms’ local muscular endurance. The key is to give just enough recovery between sets that you can have a usefully long session. If you pump out on the first set, your training effect will be almost nothing. 

Warm-ups will feature some bouldering and a few minutes of movement prep. Some athletes benefit from 2-4 minutes of threshold-level work on the air bike or rowing machine to really get the blood flowing and the breathing up.

Pick a set of rungs that you can ladder up and down on for at least a minute when fresh. This is a good place to start. If the rungs are too small…again the session duration becomes a problem. 

A good starting point is to ladder for 30 seconds, then rest for 1 minute, repeating for 10 sets. 

To advance, you can use one of the progressions below. Use only one per training block. 

1. Increase the work per set. Sticking with the 90 seconds per set framework, you can move from 30 seconds work and 1 minute rest to 40:50, 45:45, and so on. Once an athlete can go to 60:30, the rung size or reach distance needs to go up.
2. Increase the number of sets per workout. This actually aims at capacity more than power, but is an option. Program up to maybe 15 sets before splitting them into groups. Doing two groups of 6-7 sets with a long rest between will keep you more focused and performing at a higher intensity.
3. Decrease the training rung size or increase the reaches. Simply making each movement a little bit harder pays big benefits in this realm. The first time you go to the next-smaller rungs, you might not be able to stick with the same work:rest ratios. If you increase the difficulty and start to fail at, say, set 6, go ahead and stop the round, take 10 minutes’ rest, and then do a second round with the goal of getting that same 6 sets. Increase from there as fitness improves.

Two Problem Links

In the Two Problem Links session, we see a longer output of continuous climbing, so you are working at the top end of the aerobic power zone. With this in mind, the climber can be very specific with hold type, angle, and difficulty of the problems. In general, you’ll start with a good bouldering warm-up that ends with some longer problems or shortened rests – with the goal being getting a slight endurance pump on. Rest 4-6 minutes, then set up for the session. 

The standard session is 4-8 sets of two linked problems. Select problems that are around your onsight grade or just slightly easier. You will climb problem one to its end, then downclimb on open holds, but avoid resting and taking too much time. Once back close to the bottom, you will traverse to the beginning of a second problem of roughly the same difficulty, then climb that problem to the top. 

Most athletes will complete this set in 60-90 seconds. Aim to start with at least a 1:5 work:rest ratio, so if your set takes 90 seconds, rest about 8 minutes before the next set. If you see solid performance across all sets, you can increase the difficulty in the next session. Over the course of a training cycle, you can strip this rest down to probably a 1:2 work:rest ratio.

This session usually takes 35-75 minutes after warm-up.