ALT is short for ALanine Transaminase
AST is short for ASpartate Transaminase
They are enzymes that can transfer amino groups between amino acids. They exist both in the liver and in skeletal muscle since they have an important job in both tissues.
When you train hard, your muscles break, causing these enzymes to leak out into the blood. When your blood is tested, noone sees where it came from, they just se high ALT.
Your liver is (probably) fine, high AST/ALT just means your muscles are temporarily damaged. In this case.