By Matt Russ

for Triathlete magazine

One of the hardest concepts for an athlete to understand and implement is aerobic base training. It is counterintuitive to run or bike sub pace in order realize performance later in the season. It is also very difficult to take a step back from intense training performed in season, and bring the speed and pace way down. But if you have the discipline to train aerobically for a period of time (when everyone else is still hammering themselves into the ground), it will pay you dividends you want down the road.

First and foremost at the end of a season or specific training phase you need a break. I prescribe a 3-4 week transition phase at the end of each season and immediately follow it with base training. Transition is a time to rest and recover both physically and mentally. We do not take total time off because the fitness loss takes too long to make up. Instead I give my athletes maximum flexibility with their training, plenty of rest, and let them leave the electronic devices at home. This gives them time to dis-associate a bit, then refocus, before we begin structured base training. It is important to note that you cannot train hard (effectively) year round without taking regular periods of reduced volume and intensity. If you attempt to you will in all likelihood find yourself burned out, over trained, and likely injured. You will also find your performance degrading rather than improving. Most athletes build base in the fall and winter when there are not a lot of races on the calendar. If one of my athletes wants to race during base we call it a C fun / training race and do not set any performance goal, or we choose events that are longer and aerobic that will be done sub pace.

Physiology of base training

There are two basic energy systems you utilize when training for events beyond sprinting; anaerobic and aerobic. Unfortunately, you cannot build both your aerobic and anaerobic systems at the same time effectively. The idea behind aerobic base training is to train your aerobic energy system specifically and solely. Why is this important? The more work you perform aerobically, or in the presence of oxygen, the more efficient you become. Prolonged aerobic training produces muscular adaptations that improves oxygen transport to the muscles, reduces the rate of lactate formation, improves the rate of lactate removal, and increases energy production and utilization from stored fats. These adaptations occur slowly over time.

Fat is a primary fuel source for the aerobic energy system. Over the course of a base period your body learns to more readily break down and utilize fat as an energy source. As an added bonus this adaptation helps improve post exercise fat metabolism. The ability to break down and utilize fat as a fuel source is especially for long distance athletes. The fat we have in our bodies could provide enough energy to perform many distance events back to back, whereas muscle glycogen depletion can occur in as little as one hour. The less muscle glycogen you utilize, the more efficient you are. Contrary to the aerobic system, the anaerobic system consumes carbohydrate rapidly and the byproducts are lactic acid, heat, and fatigue.

Other adaptations of aerobic training include increased stroke volume of the heart, capillary density, and mitochondrial density. Stroke volume increase simply means that your heart pumps more blood per beat. Mitochondria are structures within muscle cells that produce energy from fat and carbohydrate oxidation. Think of them as tiny batteries for muscle contractions. Regular endurance training can double these structures (1). By increasing capillary density we can effectively transport more blood to the working muscles. The process of building capillaries occurs gradually. Because high stress training breaks down capillaries, base training is best for allowing the slow growth of capillaries.

Base progression

There should be progression during base season as with any other training period. I normally prescribe 10-16 weeks of aerobic base training. This will vary with athlete's fitness level, and the type of event they will be peaking for. Over the course of base I progress from the low end of the aerobic energy system and gradually proceed in steps to the high end. The heart rate zones I use fall into the 71-90% range of lactate threshold or 61-80% of max heart rate. I also incorporate specific strength training at an aerobic level. This entails different types of low cadence cycling and slow hill running or even hiking. These work outs also increase in volume throughout base. Base training is an excellent time to work on form and economy as well. As intensities increase later in the season it is harder for the athlete to concentrate and control form. By establishing good economy habits early in the season the athlete will carry them forth. It also important to keep the athlete's engaged with drills and technique work, as training at low intensity can become tedious. Base training does not mean you will never move fast. Run strides, foot speed drills, and fast pedal work should all be integrated to maintain neuromuscular firing. Towards the end of base I start power work but initiate with short bursts and full recovery between efforts.

How does this transfer into performance gain?

Let me give you a hypothetical example. Suppose athlete Sam runs a 7 min. mile at lactate threshold. His fastest aerobic pace, or aerobic threshold, is an 8 min. mile. We start off Sam's base training at the low end aerobic zones at which he runs a 9 min. mile and he begrudgingly complies. Over the course of his 12 week base program the above mentioned adaptations occur. At the end of his base season he now runs a 7:30 min. mile- aerobically. This is the base for Sam to build on for the rest of his season. Improving on the previous season is now more obtainable with proper training. If Sam's race is an IronMan in which the aerobic energy system is used predominantly, this improvement in aerobic speed is crucial.  This is where Sam will "cut his groove" on race day.

Now the hard part

The hard part of base training is having the discipline to train at these low intensities. It may mean running very slowly or even walking if you are relatively new to training. It may mean separating from your training group in order to pursue your individual goals. It also means avoiding the contest of egos that group training often turns into. If you can find a training partner with similar goals and fitness level you may be able to train with them, but more often than not what I see is a base work gone awry. Even spending short amounts of time above your aerobic zone degrades the work out.

The area between the top of the aerobic threshold and anaerobic threshold is somewhat of a no mans land of fitness. It is a mix of aerobic and anaerobic states. For the amount of effort the athlete puts forth, not a whole lot of fitness is produced. It does not train the aerobic or anaerobic energy system to a high degree. This area does have its place in training; it is just not in base season. Unfortunately this area is where I find a lot of athletes spending the majority of their seasons, which retards aerobic development. The athletes heart rate shoots up to this zone with little power or speed being produced when it gets there.

Another issue is having accurate zones. I regularly performance test my athletes in order to ensure their zones are correct and to confirm their training. After performing many of these tests, and comparing them to race data, I get a very clear estimate of lactate threshold. I use a percentage of LTHR to determine individual zones. I also recommend validation through clinical testing. I have witnessed athletes using zones that are several years old. Assuming fitness has improved over this time their zones would no longer be accurate and they may have spent an entire base season training the wrong energy system.

You have to let your anaerobic system atrophy during base. This means you will loose some of your anaerobic endurance and the ability to sustain speed near lactate threshold. Expect to loose some top end coming out of base, but this is what you are going to spend the rest of your season working on. It often takes several seasons to see the result of sound base training if you are a novice athlete. Be patient, it is a process that is slow and can not be rushed, but the sooner you get started the faster you will be.

Holloszy, J. Biochemical adaptations in muscle. Journal of Biological Chemistry 242: 2278-2282, 167

Matt Russ has coached and trained athletes up to the professional level, domestically and internationally, for over 15 years. He has achieved Elite licenses from both USA Triathlon and USA Cycling, and is a licensed USA Track and Field Coach. Matt is Head Coach and owner of The Sport Factory. He is a free lance author and his articles are regularly featured in a variety of magazines and websites. Visit sportfactory.com more information or email him at coachmatt@thesportfactory.com