Lactic Acid ≠ Soreness

After a long day benching at the gym, I sometimes wonder why my arms are so sore... this article explains why. This article talks about why lactic acid builds up in muscles and why it causes soreness. As we start to perform more strenuous exercises, we breathe faster to attain more oxygen to keep our muscles working. Although the body prefers to generate energy using oxygen, sometimes our bodies require energy production faster than we can adequately deliver oxygen. Our bodies have to produce energy without the presence of oxygen. Through glycolysis, glucose is broken down or metabolized into a substance called pyruvate through a series of steps. When oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown--and thus energy production--to continue. Sometimes the lactate levels get high because we cannot get enough oxygen over an extended period of time. This increases the acidity of the muscle cells. The same metabolic pathways that permit the breakdown of glucose to energy perform poorly in this acidic environment. This is a natural defense mechanism from the body. Eventually the body slows down, oxygen becomes available and lactate reverts back to pyruvate, allowing continued aerobic metabolism and energy for the body to recover.

 This is a diagram showing how lactate forms.

Lactic acid is not the cause of the soreness in the days to follow. Researchers who have examined lactate levels right after exercise found little correlation with the level of muscle soreness felt a few days later. Though the exact cause of delayed-onset muscle soreness is still unknown, most research suggests actual muscle cell damage and an elevated release of various metabolites into the tissue surrounding the muscle cells. These responses to extreme exercise result in an inflammatory-repair response, and are probably the  leading cause of the swelling and soreness that peaks a day or two after the event and resolves a few days later, depending on the severity of the damage.