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Are you in the Zone?

Most endurance athletes have come to realize the importance of training in levels. With improvements in technology and best practices, we’ve come to learn the necessity of spending specific amounts of time at different levels.

Michael Pellegrino
March 3, 2018

Training Levels

Most endurance athletes have come to realize the importance of training in levels. With improvements in technology and best practices, we’ve come to learn the necessity of spending specific amounts of time in different levels resulting in a physiological response by the body. In other words, getting stronger! The number of levels used can vary depending on the metrics used by the athlete in their training (ex. Heart Rate vs. Power). Regardless of the number of levels you use, all training can be simplified down to 2 basic levels: Aerobic and Anaerobic. Let’s clarify these levels and clear up some common misconceptions.

Training Levels


The term “Aerobic” has both Greek and English roots translating roughly to “air living”. Air refers to the use of oxygen in this biological (living) process. So where does this air come from?? Yep, you guessed it, it comes from breathing (respiration). Hence the full name of the process is Aerobic Respiration. Now, most folks know that breathing is required for life in animals but most have no idea why. The oxygen you inhale is actually used to extract the energy from the food that you eat which ultimately powers your muscles during training. The food contains stored energy in its chemical structure (potential chemical energy). Your cells receive the digested nutrients from the gut via blood vessels. The energy providing nutrients can be amino acids, simple sugars, glycerol, and fatty acids depending on what foods are eaten. The cell’s job is to remove the chemical potential energy from these nutrients and convert that energy to a usable form for the cell to complete its work including the important muscular contractions used in your training. To accomplish this, the food’s energy is converted to ATP (Adenosine Triphosphate). ATP is the body’s universal energy currency. All cellular processes that keep you alive and help you train are powered by ATP. The oxygen that you inhale is an important part of this process. It allows your cells to fully break down the ingested nutrients from your food resulting in approximately 30-38 molecules of ATP depending on the type of nutrient. The end product of this process is water and carbon dioxide. You actually exhale part of the food that you eat!


So, what happens if your cells have to produce ATP and there is no oxygen available at the moment? Anaerobic respiration (without oxygen) is used. Anaerobic respiration has some limitations. It only produces 2 ATP (instead of 30-38) and the by-product Lactic Acid due to the inability of the cell to fully break down the nutrients. The Lactic Acid then has to be broken down into less harmful wastes. This probably doesn’t sound very efficient but that’s because it really isn’t meant to replace Aerobic Respiration. It’s meant to augment it. Think of Anaerobic Respiration as a “Human Turbo”. This process is designed to provide a short-term turbo boost. In evolutionary terms, it was designed to give a person that extra burst when faced with a life-threatening situation. Let’s face it, someone isn’t apt to think about the lactic acid induced burning of their lungs and muscles while being chased by a bear set on making them dinner. Most of the body’s cells are still using oxygen (Aerobic Respiration) to produce the 30ish ATP per nutrient molecule. You haven’t stopped breathing while being chased. Instead, the body has devised a way to squeeze out some extra energy (ATP) from muscle cells that don’t have access to oxygen at that moment because of its increased consumption by other muscle cells. That extra ATP provides the “boost”. It does come at a cost, however. Your body can only carry this process out for around 90 seconds or so at the highest intensity levels. This is where your training comes in. Your body’s ability to increase training intensity without going into the farthest reaches of anaerobic respiration (Lactate Threshold) is highly trainable.


A common misconception is that your body switches from Aerobic to Anaerobic Respiration like a light switch. The reality is there’s a lot of “grey area” with any number of your body’s cells carrying out either at any given moment. A more accurate illustration would be a dimmer switch. During lower intensity training levels, a majority of your cells will be utilizing aerobic respiration. However, there will still be a much smaller amount of cells carrying out anaerobic respiration due to the absence of a molecule of oxygen at the precise moment of its necessity. As for exercise intensity increases, there will be a growing number of muscle cells making ATP without oxygen resulting in the dreaded lactic acid build up. As I mentioned before, appropriate training can be of great value here. The correct amount of stress for a specific period of time in the correct zone can keep that dimmer switch from becoming as bright as quickly. In other words, you can train your body to become more efficient resulting in fewer muscle cells forced to go anaerobic. The more muscle cells able to squeeze out 30ish ATP per food molecule, the more POWER!

Individualized Training Levels

The current systems of training levels use the area where the scales begin to tip between aerobic and anaerobic respiration as a baseline from which to calculate all other zones. This range is called Threshold or FTP (Functional Threshold Power) for power users. At this value lactic acid begins to be produced faster than the body can break it down. This results in a build-up leading to a burning sensation in the lungs and muscles. Aerobic training levels (ex. recovery, endurance, tempo) are below the threshold value. Anaerobic levels (ex. Functional Reserve Capacity, Anaerobic Capacity) are above it. Using these zones correctly can provide you with the maximum gains for your hard work.

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