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EDIT: The finished version of this article (with some additions, some corrections, a few extra links and a few extra FAQs) can be found here: Conditioning FAQ v2.0.
This thread is meant to provide general info on the conditioning part of the S&C equation. “Conditioning” is about achieving and sustaining the max amount of power output inside the requirements of an athlete’s sport, but in a more general sense, one could define conditioning as “not getting tired easily while doing various shit”. If that’s what you’re looking for, make yourslef comfortable and keep on reading.

Energy Systems
“Energy systems” is literally the different ways the body can use energy substrates to provide energy for muscle force production. Understanding how the different energy systems work and interact with each other to satisfy the different energy demands of the body is fundamental to understanding how to work on your conditioning.
But first, a few words about the energy substrates:
All energy comes from the main substrates: ATP (adenosine triphosphate), PCr (phosphocreatine), glycogen/glucose and fatty acids (hereby referred to as fat). ATP is the only chemical compound that can be used by the muscle fibers as energy to produce force, so basically PCr, glycogen and fat are used to create ATP, which then is used to produce power.
Basic facts about the energy substrates:
And now the energy systems:
The ATP/PCr System - very high power/very short duration
The ATP/PCr system is anaerobic (“aero” means “air”, and “anaero” means “no air”, i.e. it doesn’t use oxygen) and provides energy FAST but can only provide energy for a very short time. Power being the rate of work production, “fast energy” translates to high power production. It uses what little ATP is ready and waiting inside the muscle cell, and it also uses what little PCr is there to create new ATP. When going all out, both those substrates will be depleted within 8-10 seconds. It will generally take around 3-5 minutes for phosphocreatine stores to be nearly fully restored, a process which takes place in the mitochondria and utilizes the aerobic energy system (kind of like recharging your cellphone).
The Glycolytic System - high power/limited duration
The glycolytic system is also anaerobic, it provides energy fast (without caps!) and can provide energy for a fairly long but still limited amount of time. It uses glycogen to create new ATP, which is a pretty fast procedure but not quite as fast as PCr to ATP, and it also creates some “byproducts”. Those byproducts are metabolized by the aerobic system, but if the exercise intensity is high the aerobic metabolism can’t keep up with glycolysis and accumulation of byproducts occurs.
The main problem with the glycolytic system duration in high-intensity attempts is not the depletion of substrates, but the accumulation of byproducts (once thought to be lactic acid) that lower the pH of the muscle cells and render them useless (that’s why in the last few meters of a 400m sprint you “stiffen up” and can barely will your legs to move). Some of those byproducts are gradually metabolized in the mitochondria of the muscle cell and the rest enter the blood and are metabolized in other cells, thus the pH of the blood also drops (this process is sometimes referred to as “buffering”. A fair indicator of this procedure is the blood lactate level (Lactate accumulation, proton buffering, and pH change in ischemically exercising muscle) and the process of the blood (and the muscle cells) returning to normal levels can take north of 10 or even 20 minutes if the original lactate accumulation was really high.
The famous “anaerobic threshold” (AT), which you’ve probably heard of before, sometimes interchangeably referred to as “lactate threshold” (LT) or “onset of blood lactate accumulation” (OBLA), is basically roughly the level of continuous effort above which glycolytic byproducts accumulate. Anywhere bellow that threshold you can sustain your activity for a very long time, anywhere above that threshold fatigue will eventually occur (the further above the threshold, the faster the byproducts will accumulate, and thus the faster you will get fatigued). The terms AT, LT and OBLA are not exactly identical, for further information you can start here: http://edulife.com.br/dados\Artigos...etodos de verificacao do limiar anaerobio.pdf
The Aerobic System - low power/unlimited duration
The aerobic system provides energy slowly but can last for a fucking long time! The aerobic system is all about the mitochondria, which use glycogen (or rather, glycolytic byproducts), fat and O2, and through many many slow chemical reactions they produce ATP and CO2. No byproducts are produced and the aerobic system can go on and on for hours as the substrates are virtually unlimited. Another thing the mitochondria do is use oxygen to restore the PCr stores and to help metabolize the accumulated glycolytic byproducts (sort of like “aerobic recycling”. This little detail can have significant implications in maintaining a higher energy output, as well as in recovering faster between bouts of higher energy production. It takes a couple of minutes for the aerobic system to “wake up”, that’s why sometimes when you start running the first couple of minutes may feel more tiring until you “find your pace”.
Unlike the anaerobic systems, the aerobic system relies not only on energy substrates but also on oxygen supply. The oxygen pathway is simple: you breath, oxygen goes into your lungs, it diffuses into your blood, the hearth pumps the oxygen-rich blood through the vessels to your limbs and the oxygen is diffused from the local capillaries into your muscle cells and eventually into the mitochondria. The aerobic system can be divided in two components: the central or “oxygen transport system”, comprising of the lungs and the cardiovascular system (the heart, the blood and the blood vessels), and the peripheral or “oxygen uptake/consumption system”, comprising of the muscle capillaries and the aerobic system-related parts of the muscle cells (the number and size of the mitochondria, the myoglobin content and the various aerobic enzymes concentrations). Those two components together determine the VO2max and both components can be limiting factors to maximum aerobic power production.
Barring health-related issues (like chronic lung issues, iron deficiencies, or different forms of anemia), the main limiting factor in the oxygen transport system is the cardiac stroke volume (SV, i.e. the amount of blood your heart pumps with each beat). The most effective type of training to improve your stroke volume seems to be lower-intensity/longer-duration work, because at high intensities, as the heart rate increases, there isn’t enough time between heart beats for the ventricles to full up. Your resting heart rate (RHR) is a rough indication of your SV (generally speaking, the lower your RHR the higher your SV).
The oxygen uptake system can be significantly influenced by both lower-intensity and higher-intensity training (start here for more info). An important difference here is that, while the adaptations of the oxygen transport system can be equally applied to all types of exercise (running, swimming, MMA, etc.), the adaptations of the oxygen uptake system are muscle-specific:

Energy System Interaction
This graph shows the theoretical ATP production over time when exercising at 100% effort:
But what happens you are not doing a continuous all-out effort?
Here is the simplified description: At low intensities, the aerobic system burns fat and provides clean but slow energy. As the energy demands rise and the aerobic system alone is too slow to satisfy them, there is an increasing glycolytic system contribution and the aerobic metabolism gradually shifts from burning fat to burning glycolytic byproducts. As the intensity increases, the aerobic system reaches a point (when it crosses the AT) where it can no longer keep up with the glycolytic byproduct accumulation and the pH starts dropping. While the aerobic and glycolytic systems function in a continuum, the ATP/PCr system can be seen as a separate mechanism that provides brief bursts of energy, sort of like pushing the “nitro” button, but then needs some time to recharge.
For more details on energy system interaction, this article is a good place to start: Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise
This thread is meant to provide general info on the conditioning part of the S&C equation. “Conditioning” is about achieving and sustaining the max amount of power output inside the requirements of an athlete’s sport, but in a more general sense, one could define conditioning as “not getting tired easily while doing various shit”. If that’s what you’re looking for, make yourslef comfortable and keep on reading.

Energy Systems
“Energy systems” is literally the different ways the body can use energy substrates to provide energy for muscle force production. Understanding how the different energy systems work and interact with each other to satisfy the different energy demands of the body is fundamental to understanding how to work on your conditioning.
But first, a few words about the energy substrates:
All energy comes from the main substrates: ATP (adenosine triphosphate), PCr (phosphocreatine), glycogen/glucose and fatty acids (hereby referred to as fat). ATP is the only chemical compound that can be used by the muscle fibers as energy to produce force, so basically PCr, glycogen and fat are used to create ATP, which then is used to produce power.
Basic facts about the energy substrates:
- a very small amount of ATP is stored in the muscle cells and is ready to be used immediately
- a very small amount of PCr is stored in the muscle cells
- significant amounts of glycogen are stored in the body (in the muscles and the liver)
- the body has plenty of fat and them some (some in the muscles and most in the adipose tissue)
And now the energy systems:
The ATP/PCr System - very high power/very short duration
The ATP/PCr system is anaerobic (“aero” means “air”, and “anaero” means “no air”, i.e. it doesn’t use oxygen) and provides energy FAST but can only provide energy for a very short time. Power being the rate of work production, “fast energy” translates to high power production. It uses what little ATP is ready and waiting inside the muscle cell, and it also uses what little PCr is there to create new ATP. When going all out, both those substrates will be depleted within 8-10 seconds. It will generally take around 3-5 minutes for phosphocreatine stores to be nearly fully restored, a process which takes place in the mitochondria and utilizes the aerobic energy system (kind of like recharging your cellphone).
The Glycolytic System - high power/limited duration
The glycolytic system is also anaerobic, it provides energy fast (without caps!) and can provide energy for a fairly long but still limited amount of time. It uses glycogen to create new ATP, which is a pretty fast procedure but not quite as fast as PCr to ATP, and it also creates some “byproducts”. Those byproducts are metabolized by the aerobic system, but if the exercise intensity is high the aerobic metabolism can’t keep up with glycolysis and accumulation of byproducts occurs.
The main problem with the glycolytic system duration in high-intensity attempts is not the depletion of substrates, but the accumulation of byproducts (once thought to be lactic acid) that lower the pH of the muscle cells and render them useless (that’s why in the last few meters of a 400m sprint you “stiffen up” and can barely will your legs to move). Some of those byproducts are gradually metabolized in the mitochondria of the muscle cell and the rest enter the blood and are metabolized in other cells, thus the pH of the blood also drops (this process is sometimes referred to as “buffering”. A fair indicator of this procedure is the blood lactate level (Lactate accumulation, proton buffering, and pH change in ischemically exercising muscle) and the process of the blood (and the muscle cells) returning to normal levels can take north of 10 or even 20 minutes if the original lactate accumulation was really high.
The famous “anaerobic threshold” (AT), which you’ve probably heard of before, sometimes interchangeably referred to as “lactate threshold” (LT) or “onset of blood lactate accumulation” (OBLA), is basically roughly the level of continuous effort above which glycolytic byproducts accumulate. Anywhere bellow that threshold you can sustain your activity for a very long time, anywhere above that threshold fatigue will eventually occur (the further above the threshold, the faster the byproducts will accumulate, and thus the faster you will get fatigued). The terms AT, LT and OBLA are not exactly identical, for further information you can start here: http://edulife.com.br/dados\Artigos...etodos de verificacao do limiar anaerobio.pdf
The Aerobic System - low power/unlimited duration
The aerobic system provides energy slowly but can last for a fucking long time! The aerobic system is all about the mitochondria, which use glycogen (or rather, glycolytic byproducts), fat and O2, and through many many slow chemical reactions they produce ATP and CO2. No byproducts are produced and the aerobic system can go on and on for hours as the substrates are virtually unlimited. Another thing the mitochondria do is use oxygen to restore the PCr stores and to help metabolize the accumulated glycolytic byproducts (sort of like “aerobic recycling”. This little detail can have significant implications in maintaining a higher energy output, as well as in recovering faster between bouts of higher energy production. It takes a couple of minutes for the aerobic system to “wake up”, that’s why sometimes when you start running the first couple of minutes may feel more tiring until you “find your pace”.
Unlike the anaerobic systems, the aerobic system relies not only on energy substrates but also on oxygen supply. The oxygen pathway is simple: you breath, oxygen goes into your lungs, it diffuses into your blood, the hearth pumps the oxygen-rich blood through the vessels to your limbs and the oxygen is diffused from the local capillaries into your muscle cells and eventually into the mitochondria. The aerobic system can be divided in two components: the central or “oxygen transport system”, comprising of the lungs and the cardiovascular system (the heart, the blood and the blood vessels), and the peripheral or “oxygen uptake/consumption system”, comprising of the muscle capillaries and the aerobic system-related parts of the muscle cells (the number and size of the mitochondria, the myoglobin content and the various aerobic enzymes concentrations). Those two components together determine the VO2max and both components can be limiting factors to maximum aerobic power production.
Barring health-related issues (like chronic lung issues, iron deficiencies, or different forms of anemia), the main limiting factor in the oxygen transport system is the cardiac stroke volume (SV, i.e. the amount of blood your heart pumps with each beat). The most effective type of training to improve your stroke volume seems to be lower-intensity/longer-duration work, because at high intensities, as the heart rate increases, there isn’t enough time between heart beats for the ventricles to full up. Your resting heart rate (RHR) is a rough indication of your SV (generally speaking, the lower your RHR the higher your SV).
The oxygen uptake system can be significantly influenced by both lower-intensity and higher-intensity training (start here for more info). An important difference here is that, while the adaptations of the oxygen transport system can be equally applied to all types of exercise (running, swimming, MMA, etc.), the adaptations of the oxygen uptake system are muscle-specific:

Cycling won’t do much for you upper-body uptake system
Energy System Interaction
This graph shows the theoretical ATP production over time when exercising at 100% effort:
But what happens you are not doing a continuous all-out effort?
Here is the simplified description: At low intensities, the aerobic system burns fat and provides clean but slow energy. As the energy demands rise and the aerobic system alone is too slow to satisfy them, there is an increasing glycolytic system contribution and the aerobic metabolism gradually shifts from burning fat to burning glycolytic byproducts. As the intensity increases, the aerobic system reaches a point (when it crosses the AT) where it can no longer keep up with the glycolytic byproduct accumulation and the pH starts dropping. While the aerobic and glycolytic systems function in a continuum, the ATP/PCr system can be seen as a separate mechanism that provides brief bursts of energy, sort of like pushing the “nitro” button, but then needs some time to recharge.
For more details on energy system interaction, this article is a good place to start: Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise
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