Moderate evidence

Muscle soreness is not a valid indicator of how well a session worked.

In practice

Soreness mostly tracks novelty — a new exercise, a long eccentric, a layoff. A session that leaves you fine can be a better session than one that leaves you wrecked. Judge training by whether the numbers move, not by how you feel two days later.

What it doesn't say

Soreness isn't meaningless either: a sudden jump in it usually means you added too much too fast.

Source

• Schoenfeld BJ, Contreras B (2013). Is postexercise muscle soreness a valid indicator of muscular adaptations?. Strength & Conditioning Journal, 35(5):16–21. doi.org/10.1519/SSC.0b013e3182a61820