ALT and AST are the two transaminases you see on almost every liver panel. ALT (ALAT) is fairly liver-specific, while AST (ASAT) also sits in your muscles and heart. That single difference explains why a raised AST in a keen lifter often has nothing to do with the liver.
I run into this pattern so often that I almost always explain it: a high AST just after a heavy leg session is usually muscle, not a liver problem.
What are ALT and AST?
ALT and AST are enzymes released when cells get damaged. If liver cells break down, they leak these enzymes into your blood. Measure them and you get a sense of how your liver cells are doing.
The difference lies in where the enzymes come from. ALT sits mostly in your liver, so a raised ALT points fairly precisely at your liver. AST also comes from muscle tissue and heart, which makes the source less clear-cut.
The full picture of your liver values is in the pillar liver values explained. For the bile-duct marker, read high gamma-GT.
The difference between ALT and AST
The ratio between ALT and AST often hints at the source. If mainly your ALT is raised, that points more precisely at your liver. If mainly your AST stands out, especially with a high CK, muscle is a likely explanation.
This table sets the two side by side. Use it as a reading guide, not a diagnosis.
| Marker | Where it mainly comes from | What a rise can mean |
|---|---|---|
| ALT (ALAT) | Mainly liver | Fairly targeted signal toward the liver |
| AST (ASAT) | Liver, but also muscle and heart | Can be muscle, especially after hard training |
| AST high, ALT normal | Source often lies outside the liver | Think muscle load, check CK |
| ALT and AST high together | Liver cells are being irritated | Fatty liver, alcohol, substances |
According to Thuisarts.nl, raised transaminases can fit fatty liver, alcohol or medication among other things. The context decides what is likely.
Why does AST rise after training?
Heavy or unusual strength training damages muscle fibres a little, and AST is released with that. Your liver is fine, your muscles simply worked hard. This is the most-missed explanation in athletes.
A good check is your CK value, a true muscle enzyme. If AST and CK rise together while ALT stays calm, that strongly points to muscle. What that pattern looks like is in spotting overtraining through your blood values.
You see the same effect with creatinine, which comes out higher with a lot of muscle mass without your kidneys working less. We explain that in high creatinine from muscle mass.
My advice: do not test within two to three days of a hard session if you want to read your liver honestly.
When does it really point to your liver?
If your ALT stays raised after you have taken a few days of rest and drunk no alcohol, that weighs more. A persistently high ALT apart from training is a clearer liver signal than a one-off AST spike.
Substances play a role too. The Dopingautoriteit lists liver dysfunction as a possible side effect of anabolic substances, and the RIVM raises questions about the safety of some supplements. More on that in liver values and substances.
What can you do about high transaminases?
Repeat the measurement after a few days of rest, without alcohol and hard training. If you then see a more normal value, training was probably the culprit. If it stays high, that belongs with your GP.
You can have ALT and AST drawn together with the 360 Health test and look again after a few months. That way you track the trend instead of a single number.
What a raised result can mean further is in elevated liver values: causes and symptoms.
Frequently asked questions
Is a high AST always a liver problem? No. AST also comes from muscle, so after hard training it can be temporarily high without your liver having any issue.
What does a high ALT mean? ALT is fairly liver-specific, so a persistently high ALT points more precisely toward your liver. Discuss that with your GP.
What is the AST/ALT ratio? That is the ratio between the two. Doctors sometimes use it as a hint about the possible cause, but it is not proof.
How long after training are the values normal again? That varies per person and per session, often a few days. A repeat measurement after rest gives you a fairer picture.
Conclusion
ALT and AST look alike, but the difference is exactly what athletes should know. ALT points more precisely at the liver, AST can simply be your leg day. Read them together, and watch your CK.
Measure rested, look at the pattern, and discuss a persistently high ALT with your GP.
References
- Thuisarts.nl. The liver tests in my blood are not good. Accessed 2026.
- Dopingautoriteit. Anabolic substances. Accessed 2026.
- RIVM. Use and safety of doping and sports nutrition supplements. Accessed 2026.
Disclaimer
Every blood test result includes a professional assessment from a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. For treatment decisions, discuss your results with your GP.
Tagi
Autor
