I often wondered why anaerobic and aerobic exercises are named as they are. Surely, while running, you should not be out of breath to avoid “switching to anaerobic metabolism”. But why is it called anaerobic metabolism when doing short bursts of weight training even though I am barely out of breath? Recently, I refreshed my biology class 11 knowledge with the help of wikipedia and want to share my findings.
Adenosine Triphosphate (ATP) – The Body’s Energy Currency
To make a muscle work, it needs energy. That energy is primarily generated when ATP (Adenosine Triphosphate) splits off one phosphate group, turning into ADP (Adenosine Diphosphate) and releasing energy in the process.
ATP + H2O → ADP + P + Energy
However, we only have a tiny reserve of ATP in our muscle cells, enough for maybe 2–3 seconds of maximal contraction. To provide a constant stream of energy, ATP needs to resynthesized from other stored energy sources like glycogen and fats (which aren’t always stored right in the muscle cells). An important part of this resynthesis relies on energy carriers such as NADH and FADH₂, which are produced during earlier breakdown steps of these fuels. Inside the mitochondria, these carriers are then used to generate most of our ATP.
wikipedia bild
Aerobic Metabolism
Aerob means, that this kind of metabolismn is done under use of oxygen. Although this proceses produces a lot of ATP, it takes several sub steps and is therefore slower to deliver energy.
aerob-glykolytic
In a first step, glycogen is broken down to pyruvate in the cell’s cytoplasm (glycolysis). If oxygen is available, the pyruvate enters the powerhouse of the cell – the mitochondria – where oxidative decarboxylation is performed, converting pyruvate into Acetyl-CoA and releasing one CO₂ molecule. In the citric acid cycle, Acetyl-CoA is completely processed, generating the majority of NADH (and some FADH₂). These electron carriers are then used in oxidative phosphorylation to produce the majority of ATP.
| Step | Whats Happening |
|---|---|
| Glycolysis | Glukogen → Pyruvat + ATP + NADH |
| Oxidative Decarboxylation | Pyruvat → Acetyl CoA + NADH + CO₂ |
| Citric Acid Cycle | Acetyl CoA → NADH + FADH₂ + ATP + CO₂ |
| Oxidative Phosphorylation | NADH + FADH₂ + O₂ → ATP + H₂O |
We can simplify it to:
Glycogen + Oxygen → Water + Carbon Dioxide + Energy
aerob-lipolytic
Fats consist of long hydrocarbon chains that, given enough time, can be broken down in the mitochondria via β-oxidation, step by step, into Acetyl-CoA. From there, they follow the same path as glucose: into the citric acid cycle and then into oxidative phosphorylation to generate Energy.
Fats + Oxygen → Water + Carbon Dioxide + Energy
Anaerobic Metabolism
Anaerobic metabolism kicks in when oxygen supply can’t keep up with demand. It’s fast but produces limited energy. There are two main types: There are two main types: anaerobic alactic (no lactate produced) and anaerobic lactic (lactate produced).
Anaerob-Alactazid – Phosphat metabolism
After the short burst from the limited ATP stored in the muscle cells is used up, creatine phosphate (also stored directly in the muscles) can donate its phosphate group to quickly regenerate ATP.
ADP + Creatine Phosphate → ATP + Creatine
Anaerob Lactacid – Glycolysis Without Oxygen
When the demand for energy is high and oxygen delivery can’t keep up, pyruvate (from the breakdown of glycogen in the glycolysis) is converted into lactate in the muscle’s cytoplasm, producing a small amount of ATP in the process.
Glycogen → ATP + Lactate
Lactate is released into the bloodstream and can later be converted back into pyruvate for use in the citric acid cycle or into glucose via gluconeogenesis. It’s not harmful by itself, but when it accumulate, the associated hydrogen ions cause an increase in acidity (also called acidosis). This slows enzyme activity and muscle contraction, which is a protective mechanism to prevent damage to proteins, but also contributes to the feeling of fatigue.
So what did we learn?
Our muscles store only a tiny amount of ATP, which is enough for a couple of seconds of work. We rely on different systems to replenish our ATP supply.
Aerobic metabolism uses oxygen. It’s slower to start but produces a lot of energy and can keep us going for a long time. Especially
Anaerobic metabolism doesn’t use oxygen. It’s fast and powerful but can’t be sustained for long, either because the fuel runs out quickly (creatine phosphate) or because acidity builds up (lactate), making the muscles slow down.
Training Implications
Weight Training: Primarily involves anaerobic metabolism due to the need for quick energy bursts during short, intense efforts. The body relies on ATP and creatine phosphate for immediate energy. Supplementing with creatine can enhance the storage of creatine phosphate in muscle cells allowing for a greater reserve of quick energy. A side effect is that the high concentration of creatine in the muscle cells draws water into the cells through osmosis.
Cardio Training: Relies heavily on aerobic metabolism, which can sustain energy production for long periods. Fat metabolism needs a short warm-up period and typically becomes a significant fuel source only after about 20 minutes of exercise.
Specifically when running, we want to improve three main capabilities:
- the aerobic base, which allows us to sustain effort for long periods;
- VO₂max, an indicator of how much oxygen our body can use during intense exercise;
- and the lactate threshold, the highest intensity we can maintain until we reach the tipping point where lactate is produced faster than it can be cleared, and the resulting acidity forces us to slow down (https://link.springer.com/chapter/10.1007/978-3-642-85404-0_4).
Improving Aerobic Base (Zone 2 Running)
Running at a low heart-rate (Zone 2) improves your aerobic foundation by:
- Stimulating mitochondrial growth in the muscle cells, which boosts energy production efficiency (https://doi.org/10.1007/s40279-024-02120-2) .
- Increasing the capillary network around muscle fibers, improving oxygen delivery (https://doi.org/10.1007/s40279-024-02120-2).
- while offering a low-fatigue training zone, so you can do it savely, frequently and build endurance steadily.
however volume is important. As paper point out etc
3. Practical Implication
- If you’re sedentary or doing only 2–3 h/week → Paper A is more relevant (you need vigorous exercise too).
- If you’re training long hours (athletes, or 6–10+ h/week amateurs) → Paper B’s rationale holds: Zone 2 gives the biggest “return” without burning you out.
- Both agree: Zone 2 should not replace all other intensities, but its relative importance depends on your training volume.
✅ So: They don’t directly contradict — they complement. One zooms in on why Zone 2 works, the other zooms out and says “yes, but context matters.”
Improving VO₂ max (Interval Training)
To improve the maximum amount of oxygen our body can use during intense exercises, we need to push our heart, lungs, and muscles close to their limits, forcing them to adapt. We can do this most effectively by doing High-intensity aerobic interval training (https://pubmed.ncbi.nlm.nih.gov/17414804/). VO₂ max is determined by three key factors (Fick equation):
- Stroke volume — the amount of blood the heart pumps per beat.
- Oxygen extraction — the muscles’ ability to pull oxygen from the blood.
- Maximal cardiac output — the total amount of blood delivered to working muscles per minute.
Improving Lactate Threshold (Tempo Runs)
of course if you do one thing you also exercise the other thing
https://www.nature.com/articles/s41392-022-01151-3
