The problem is that after 10 seconds of contraction time, the ATP fuel extinguishes and to support further muscle contraction, glycolysis (glycogen burning) has to kick in. Lactic acid is a byproduct of that mechanism. Lactic acid is what causes the burning sensation at the end of the set. When too much lactic acid is produced, your muscle contractions stop, forcing you to stop the set. By taking creatine, you can extend the 10-second limit of your ATP system because creatine provides ADP, the phosphate molecule that it is missing. By upgrading your body's ability to regenerate ATP, you can exercise longer and harder because you minimize your lactic acid production. You will be able to take your sets to the next level and reduce fatigue levels. More volume, strength and recovery equal more muscle mass.