Soreness comes from lactic acid buildup: It’s an often-quoted principle that the delayed onset muscle soreness (DOMS) you feel in the days after your workout is from lactic acid in your body. In fact, DOMS is a symptom of micro tears in the muscles that happen when you work out. Lactic acid does play a part in your workout, however, since it is the cause of that burning sensation you feel when working your muscles. It actually fuels muscles to help you work out longer, so pushing past that burning sensation will help you increase your strength and endurance.
What to do:
As a follow-up: What can you do to prevent/ alleviate muscle soreness?
Proper light cardio/ dynamic stretching as a warm-up and a proper cool-down afterwards
Apply Ice after a workout
Anti-inflammatories like ibuprofen (not really recommended if you can help it. I wish we had Ibuprofen gel available in the US…),
Massage (use a foam roller), exercise (yep!),
Moderate amounts of protein after a workout (like that found in BB’s Results & Recovery Drink.) :)
Read this article about other Strength-Training Myths. :)