Hard Training Can Raise Your Liver Enzymes Too

A lifter gets routine bloodwork back and two numbers on the liver panel, AST and ALT, are flagged high. The usual reaction is to assume the liver is in trouble. A 2020 review in the Journal of Clinical and Translational Hepatology looked at why people who lift hard so often get these flags, and its main point is that the same two enzymes leak out of damaged muscle as well as damaged liver. A high AST or ALT in someone who trains hard isn't a diagnosis on its own. It's a question about where the enzyme came from.

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1. What AST and ALT are, and where they live

AST and ALT are enzymes that move amino groups between molecules. Doctors measure them routinely to screen for liver disease, but neither one lives only in the liver.

AST is found, from highest to lowest concentration, in the liver, heart, skeletal muscle, kidney, brain, pancreas, lungs and blood cells. ALT is concentrated mainly in the liver, which is why it's considered the more liver-specific of the two. It still shows up after muscle damage, though.

The two also clear from the blood at different speeds. The review gives AST's half-life as about 17 hours for the form found in the cell fluid and about 87 hours for the form inside mitochondria, which most labs don't measure separately. ALT's half-life is around 47 to 48 hours. That difference matters later, because it changes what a panel looks like depending on which day the blood is drawn.