This Aerobic Base Phase also known as the Base Phase consists those dreaded long runs and easy miles with minimal speed work. This phase tests the patience of an athlete like nothing else.
Since we runners spend so much of our time in the base phase, it makes sense to understand how it makes us more efficient runners. So let's understand the process.
To run we need: Energy
Energy comes from: Food
Food converts to energy using: Oxygen
Energy is produced in: Mitochondria
Oxygen is carried by: Red Blood Cells (RBC)
RBC are in the: Blood
Blood is pumped by: Heart.
It makes sense that more oxygen will give our body more energy provided we consume sufficient food.
Within the first few weeks of the base phase, the body creates more red blood cells to adapt to the running load.
Slowly as a couple of weeks pass, the left ventricle of our heart which is responsible for pumping blood to our body increases in volume. More volume means that with every beat, more blood is pumped throughout the body. A lower resting heart rate shows that your heart is capable of pumping more blood in one beat.
As you progress in the base phase, more structural changes take place:
The capillaries around the muscles that carry blood to muscles increase in number and the mitochondria which produces energy, increase in number and volume.
With an efficient heart pumping a higher volume of blood that contains a larger number of RBC (carriers of oxygen), our body carries a lot more oxygen to the working muscles. Now the oxygen actually reaches the muscles because of the capillaries, and the higher number of mitochondria help in using this oxygen to create more energy. More energy means faster running. The efficiency of the body is dramatically improved in the base phase without much speed work and so you can see your speed dramatically increase.
With all the long runs, the base phase also builds fatigue resistance which prevents the body from tiring out soon and also helps prevent injury by building strength into those muscles.
The base building phase has tremendous benefits if done right. So the next time you're on that long run or just logging those easy miles, know that it's not for nothing. Your body is slowly but surely preparing for the rigours of the next challenge: The Anaerobic Phase.