Often, one of the hardest concepts for triathletes to understand and implement is the notion of base training. The idea of running slowly to boost performance later in the season can seem counterintuitive. It is also difficult to hold oneself back, but if you have the discipline to train aerobically this winter when everyone else is hammering away, it will pay dividends down the road.
Physiology of Base Training
There are two basic energy systems you use when training: anaerobic and aerobic. Unfortunately, you cannot simultaneously maximize both your aerobic and anaerobic systems. The idea behind base training is to train your aerobic energy system specifically. Why is this important? The more work you perform aerobically the more efficient this system will become.
Prolonged aerobic training produces muscular adaptations that improve oxygen transport to the muscles, reduces the rate of lactate formation, improves the rate of lactate removal, and increases energy production and utilization.
Fat is a primary fuel source for the aerobic energy system. Over the course of a base-training period, your body learns to readily break down and utilize fat as an energy source. The fat we currently have stored in our bodies could provide enough energy to perform many marathons back to back, whereas muscle glycogen depletion can occur in as little as one hour.
Other physiological adaptations of aerobic training include increased stroke volume of the heart, capillary density and mitochondrial density. Stroke-volume increase simply means 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 number of these structures1.
By increasing capillary density, we can effectively transport more blood to working muscles. The process of building capillaries occurs gradually. Because high-stress, high-impact running breaks down capillaries, base training is best to promote the slow growth of capillaries.
Base Progression
Over the course of the 12- to 16-week base phase, training should gradually progress from the low end (i.e. 71 percent of lactate threshold (LT), or around 61 percent of max heart rate) of the aerobic energy system to the high end (i.e. 90 percent of LT and 80 percent of max heart rate).
I also incorporate specific strength training at an aerobic level. This entails slow hill running or even walking. These workouts increase in duration throughout the base phase.
Base training is an excellent time to work on form and economy as well, since, as intensities increase later in the season, it becomes harder for an athlete to concentrate on form. Toward the end of the base phase I start power work but use brief durations and full recovery between efforts.
How Does This Transfer Into Performance Gain?
Let me give you a hypothetical example. Suppose Sam runs a seven-minute mile at lactate threshold (85 to 90 percent of max heart rate). His fastest aerobic pace, or aerobic threshold (around 65 percent of max heart rate), is an eight-minute mile. We start off Sam's base training at the low-end aerobic zones, at which he runs nine-minute miles. At the end of his 12-week base phase, Sam is able to run 7:30 miles aerobically. This is the base for Sam to build on for the rest of his season.
The hard part of base training is having the discipline to train at these low intensities, because even spending short amounts of time above your aerobic zone spoils the workout. The area between the top of the aerobic threshold and the anaerobic threshold is somewhat of a no-man's-land of fitness since such intensities do not train the aerobic or anaerobic energy systems effectively. Unfortunately, however, this area is where I find a lot of athletes spending the majority of their seasons.
The bottom line is you have to let your anaerobic system atrophy during the base phase. This means you will lose some of your anaerobic endurance, so expect to surrender some top-end speed coming out of your base phase, but take comfort in knowing this is what you are going to spend the rest of your season working on.
It often takes several seasons to see the results of sound base training if you are a novice athlete. Be patient; it is a slow process that cannot be rushed, but the sooner you get started the faster you will be.