Physiology and Metabolism

Rather than rewrite a whole section on the physiology of endurance, if you are unfamiliar with this topic, please review the Physiology here. Or this subject is handled in depth in the Physiology chapter 2 of Training for the Uphill Athlete.

Here is a summary of metabolism as it relates to endurance:

• Your speed is a function of your working muscles’ ATP recycling rate.
• ATP can be recycled by the aerobic and the anaerobic metabolic pathways.
• Your endurance, the duration of that speed, is a function of which metabolic pathway (aerobic or anaerobic) does most of the recycling.
• Both systems are essential and contribute to the total ATP demand at different
  percentages depending on the exercise intensity.
• Aerobic ATP production is used for low-intensity exercise, whose duration is virtually unlimited due to its use of fat for fuel and the vast fat stored in even the leanest athlete.
• The anaerobic pathway should* be used mainly for high-intensity exercise.
• Anaerobic ATP production is limited in duration by the relatively small stores of glycogen.
• Anaerobic ATP production is limited in intensity by the accumulation of the metabolic by-product lactate.

*the should is what this article is going to discuss.

The greater the capacity of the aerobic metabolic system to recycle ATP, the less you will need to rely on the anaerobic system with its inherent downsides. Increased aerobic capacity should be the goal of all endurance athletes interested in improving their performance. Unfortunately, many athletes, even some who consider themselves very fit, suffer from an underdeveloped aerobic system. It is so common that Phil Maffetone coined the term Aerobic Deficiency Syndrome and first described it to me during a chance meeting in 1985.

How can you tell if you have ADS? Here are some tests you can perform to decide for yourself.

• Do your breathing rate and depth increase a lot with the slightest uphill?
• When out for more than an hour of continuous exercise, do you need to eat a gel per hour, or do you bonk?
• Are you unable to carry on a conversation in complete sentences or breathe through your nose during most of your endurance training?
• Are you one of those exercisers that feels you need to end each workout exhausted?
• Have you been swept up in one of the fitness fads like Cross Fit, Orange Theory, P90x, Boot Camp, or similar high-intensity exercise programs?

If any of these apply to you, there is a very good chance you are aerobically deficient.  The implications of aerobic deficiency on performance are twofold.  First, the glycogen fuel tank is tiny compared to the fat fuel tank. So you risk running out of fuel before your event is finished. Second, lactate accumulation beyond a certain level (Anaerobic Threshold, Maximum Lactate Steady State, and Lactate Threshold are common names) will limit the speed you can sustain for more than a few minutes before being forced to slow.

How this Affects Your Endurance

If you want to run, ski, or climb faster for longer, you must address aerobic deficiency before you get overly concerned with high-intensity training. But that is the opposite of how most people approach aerobic exercise. There is only one way to increase that aerobic ATP recycling rate. That is, with a high volume of activity below the capacity of the aerobic system to produce ATP without much involvement of the anaerobic system.  It is nearly impossible to reduce the involvement of the anaerobic system to zero. But with proper training you minimize it for all intensities. We call this aerobic base training. Famed Soviet sports scientist Yuri Verkhoshansky coined the very descriptive term “Anti Glycolytic” training since it minimizes the use of glycogen for fuel.

Increasing speed while minimizing glycogen use is the basis for all the training methods used by the most successful endurance athletes. The inexperienced endurance athlete often misses that adding much (and in severe ADS cases, ANY) high-intensity training will reduce that all-important aerobic capacity and slow the needed improvement.

For those worst afflicted with ADS, the pace and perceived exertion will be so slow/easy that it is hard for them to accept that this could have a training effect. These folks think they need to “feel” like they are training. What they have done with the almost exclusive use of higher-intensity training is detrain their aerobic system to such a low state that it can support only a slow jogging pace. Some need aerobic base training the most and sometimes push back against it the most.

ADS sufferers are slow at aerobic efforts because their aerobic system is so poorly trained that it can only supply enough ATP to support very slow jogging or sometimes just walking. But it need not be like that. The marathon is an event that is competed at one’s maximum aerobic capacity. A world-class male marathoner can sustain a sub-5min/mile pace for 26 miles while in the same metabolic state as a 4-hour marathoner.  The point is that aerobic does not mean slow. It is only slow if your aerobic capacity is low.

It Ain’t Rocket Surgery

The good news is that this quality is one of the easiest physical properties to improve in the endurance realm. All it takes is patience and consistency. Patience because it takes time. Training harder will not shorten this process. It will slow the process. Consistency because the aerobic system needs frequent stimuli to get the message that a change is necessary and make the appropriate adaptations. If you train too infrequently, the aerobic system reverts to its untrained state. The body is amazingly adept at eliminating unneeded transformations that cost it something to maintain. How frequent is enough? That depends on your fitness and goals. For someone just starting on this ADS journey, it might be 2x a week. That world-class marathoner I mentioned above will need daily and often twice-daily training sessions to maintain and build the aerobic system’s capacity.

Specificity plays a role in this training. For general fitness, any aerobic activity will help. Swimming, rowing, and cycling are great exercises for general aerobic fitness. However, if you are engaging in a foot-borne activity like mountain climbing or running, you should also try to do most of your aerobic base training in a foot-borne modality.

Doing it Right

To pinpoint the maximum capacity of your aerobic system, usually called the aerobic threshold. To quantify the degree of your aerobic deficiency, there are some more involved tests you can conduct, from going to a lab and spending hundreds of dollars for a gas exchange test to the heart rate drift test that I explain in another article about aerobic assessment. But for now, let’s assume you have answered yes to several of the above bulleted test questions.

A very effective low-tech methods of ensuring you are not training at too high an intensity is breathing through your nose or carrying on a conversation while exercising. If you can do those things, you are, almost without a doubt, under your aerobic threshold and getting the maximum training effect for your aerobic metabolic system. This is the fastest way to remedy ADS. We have used this method successfully with thousands of athletes over several decades. It works! But you must be patient.

Rules of Thumb

The aerobic needle will move very slowly if you do less than 3 hours of aerobic base training per week. Do not expect a noticeable improvement in your aerobic pace in less than six months. If you consistently get in 5-6 hours a week of aerobic base training, you will probably notice an increase in aerobic pace in 3-4 months. Things pick up when you hit 8 hours a week, and we have seen people cure ADS in 2-3 months.

Gaging Improvement

What do we mean by “cure ADS”?  How do you know when you have improved your aerobic capacity?  Initially, both your heart rate AND pace will improve at the same time.  Eventually doing the course of aerobic base training your aerobic threshold heart rate will cease to climb in lock step with your pace.  However, with continued aerobic base training (below the aerobic threshold) your pace will continue to increase. We have seen athletes improve their aerobic threshold running pace continuously for 10 years.  That is how the elite marathoners mentioned above keep getting faster and faster.

Since you are interested in improving your performance rather than just your heart rate, the pace you can move (running, hiking up hill, etc) is something you can track with an aerobic threshold test or even casually observe when you training on the same trail frequently. Are you moving faster than a month ago while maintaining the same heart rate?

At some point on your journey to cure your ADS you no longer be moving slowly.  Z2 will no longer feel easy.  In fact Z2 can become very demanding to the neuromuscular system.  Referring back to the marathon example; running sub 5 minute miles takes a lot of muscle power.  Those elite athletes may be in the same metabolic state as someone running a 7 minute mile pace but they are producing significantly more power.  The same could be said for improving your aerobic threshold pace from 13 minute miles to 10 minute miles.  To run faster you have to produce more muscle power. That speed takes nervous system energy and is much more fatiguing than when you started this ADS journey because your aerobic metabolic system is now able to supply a great deal more energy.

We’ve discovered through testing athletes and from decades of observations that when the spread between the aerobic and anaerobic thresholds is 10% or less measured either by heart rate or pace the athlete has “cured”any aerobic deficiency and has reached good balance between the aerobic and anaerobic metabolic systems.

When you reach this level of fitness and your pace at aerobic threshold is fast enough to be quite fatiguing you must make adjustments in your training to account for the increased neurological muscular stress imposed by the faster pace.  Zone 2 running, skiing and even hiking will become taxing enough that you will need to reduce that Zone 2 training volume significantly to avoid over training. You’ll replace it with Zone 1 training.   At this same time you can begin to introduce more Zone 3 and even some Zone 4 training into your overall plan.