Building An Aerobic Base
By Sarah Willis PhD.
We break down the macromolecules of our nutrition lifestyle, primarily carbohydrates and fats as our fuels. As we consume foods which contain these molecules, we begin chemical digestion and break down glucose for energy. This process of aerobic metabolism or cellular respiration starts with glycolysis as we break down glucose to pyruvate, then pyruvate oxidation which leads to the Krebs cycle (a.k.a., citric acid cycle) where we have products of NADH and FADH2 (these are electron carriers (like a truck that carries the electrons produced from the breakdown of molecules like glucose). These electron carriers deliver to the electron transport chain and begin the generation of ATP (the main energy currency of the cell). Thanks to the electron transport chain, initiated through oxidative phosphorylation (aerobic), we can produce many ATP – this is our most efficient energy metabolism.
Throughout a training year, you may have noticed that the workouts become less demanding, and activities become easier as a result of the incredible base we build as whole-body endurance athletes. This is stimulated by many hours spent at low intensities developing our aerobic metabolism. Additionally aiding our ability to practice technique in a fluid, relaxed, and smooth way to adequately deliver oxygen to our tissues while producing a lot of energy through aerobic metabolism and effectively burning primarily fats.
As skiers, we normally start the training season by building a base or a strong foundation on which to stand as we gear up for the season ahead. Having a base of fitness is a main goal of this period of training. This is related to the total volume of training and usually includes days and weeks of building back into the duration of sessions. In addition, strength training is in a building stage at this time of year – more on that another day. Let’s keep thinking about the volume and how this first period of the year works to improve our fitness. This is directly proportionate to the training load of the year and how your plan is developed regarding the number of hours of training in the coming season.
The purpose of building an aerobic base is three-fold; creating a foundation for sustained (endurance) aerobic exercise, improving cardiorespiratory function, and preparing the body for higher-intensity training. As mentioned above, it is about creating a foundation and building from the bottom of the pyramid. This foundation allows solid support for the body to set the tone and prepare physiologically to handle the demands of exercise and increase performance.
In relation to endurance, we often associate that with physiological terms such as aerobic metabolism (the same as oxidative metabolism). This means that we are generating energy with the presence of oxygen. Sometimes I think about ‘air’ as it sounds like ‘aerobic’ to help me remember that aerobic metabolism is with the presence of oxygen (whereas, anaerobic is without oxygen present).
We break down the macromolecules of our nutrition lifestyle, primarily carbohydrates and fats as our fuels. As we consume foods which contain these molecules, we begin chemical digestion and break down glucose for energy. This process of aerobic metabolism or cellular respiration starts with glycolysis as we break down glucose to pyruvate, then pyruvate oxidation which leads to the Krebs cycle (a.k.a., citric acid cycle) where we have products of NADH and FADH2 (these are electron carriers (like a truck that carries the electrons produced from the breakdown of molecules like glucose). These electron carriers deliver to the electron transport chain and begin the generation of ATP (the main energy currency of the cell). Thanks to the electron transport chain, initiated through oxidative phosphorylation (aerobic), we can produce many ATP – this is our most efficient energy metabolism.
When we assess gas exchange during exercise (think exercise testing with a mask), we measure several parameters including the volume of oxygen consumption (VO2) and the volume of carbon dioxide exhaled (VCO2). From the ratio of these parameters (VCO2/VO2) we have the respiratory exchange ratio (RER, a.k.a. – respiratory quotient). When the RER is <0.7 we are burning primarily fats, when RER is between 0.7 and 1.0 we use a mix of both fat and carbohydrates, while when RER is > 1.0 we utilize primarily carbohydrates. The more carbon dioxide we exhale, the harder we work and the more we use anaerobic metabolism (production of ATP without the presence of oxygen). Therefore, the more efficient we can be to exercise at lower intensities (RER < 1.0) the more aerobic/oxidative metabolism we utilize for energy, and we can sustain effort for longer. Yes, here comes the endurance! To be clear, energy production is most effective with aerobic metabolism. The more energy we can produce, the faster you can run/ski/bike using your aerobic energy systems and the faster you can race. So, we need to ‘get good’ at burning fats and using less energy to perform a given workload. And yes, this does translate to enhancing our fat metabolism and is effective for weight loss depending on what lifestyle and nutritional choices we make.
The more we train at lower intensities (RER < 1.0, and even more appropriately ≤ 0.8), the more efficient our bodies become at delivering and diffusing oxygen to our working tissues. So take these volume sessions in early season slow, refine your physiology in the easy lower intensities to build a foundation for the remainder of the season. In time, this will translate to us moving at higher speeds with less effort and becoming more economical in relation to how much energy it costs us to move at a given speed (running/skiing economy).
Therefore, the big goal of base training in late spring and throughout the summer is to increase training volume without excessively stressing the body. It is also worth mentioning that this will transition to improve the body’s ability to recover. In a special way, the body becomes ‘so efficient’ that it is quicker at recovering from training sessions. This is one way to know you are becoming more fit 😊
At this point, we have only briefly mentioned the cardiorespiratory benefits of endurance exercise. Let’s dig in there a bit more. We know that with more training we strengthen our heart and lungs, ultimately improving our ability to deliver oxygen to our working muscles. But what exactly is happening there? Specifically, the left ventricle (which pumps blood from the heart to the rest of the body) increases in volume. This means it can eject more blood with each beat. It is a structural change in the myocardium, or muscle tissue of the heart that gets stronger – especially in this chamber. Over time, this will lead to more blood circulating, so fewer beats are required to circulate the same amount of blood. Additionally, our bodies build more capillaries around the muscle cells to make the exchange between oxygen and carbon dioxide. Having more capillaries and close by will increase the efficiency of the diffusion of oxygen into the muscle cells, this improves the amount of work and the ease at which work can be completed. Another adaptation is a greater number of mitochondria (the organelle within the cell which energy is created – the “powerhouse of the cell”). But not only increasing the number, also the size of the mitochondria to be able to produce even more energy; and the body even moves them closer to the cell wall, so the transfer of oxygen is even faster and more effective. Wow!
This process of building a strong base includes increasing the number of red blood cells in your blood (kind of like strength training for your blood). This is important, as red blood cells have proteins called hemoglobin that carry oxygen (and carbon dioxide) throughout your blood stream. When we have more red blood cells, we have more hemoglobin and greater capacity for carrying oxygen.
Not only does this foundational base help us to sustain effort for longer endurance durations, it also provides a foundation (a wide-based pyramid) allowing for progression in intensity. As the year progresses, the more solid preparation of the base training will allow for interval training and high-intensity intervals with lower risks for overreaching or injuries.
Having a solid base or foundation of lower intensity will help in a multitude of reasons as the season progresses. Namely, increasing the durability of the musculoskeletal system, burning fats for longer and saving (sparing) glycogen, increasing capacities of both fast and slow-twitch muscle fibers, and developing a resistance to fatigue in that we can endure longer and longer durations of activities.
There are many benefits of preparing a solid foundation of aerobic training, which all correlated to improved performance (can lead to increased VO2max, improved cardiac output, and overall better performance). Think of it as priming the engine (cardiovascular system) before a big season. Can’t wait to join you out there as we build into the year ahead!