What does lactic acid buildup primarily cause?

The correct answer is that lactic acid buildup primarily causes soreness immediately following a workout. When muscles engage in high-intensity exercise, they may not receive enough oxygen to produce energy solely through aerobic metabolism. As a result, the body resorts to anaerobic metabolism, which leads to the production of lactic acid as a byproduct. This lactic acid accumulation can lead to the sensation of soreness and fatigue in the muscles, especially during and shortly after intense physical activity.

This phenomenon is often referred to as delayed onset muscle soreness (DOMS), which typically sets in after the workout session has completed, sometimes peaking 24 to 72 hours later. The presence of lactic acid is a temporary condition that subsides as the body clears it from the muscles and restores balance.

The other options relate to various aspects of exercise physiology but do not accurately capture the primary effect of lactic acid buildup. Long-term muscle fatigue is more related to overall training volume and recovery, while increased blood flow to the muscle occurs as an adaptive mechanism to support exercise performance but is not caused by lactic acid. A decrease in performance can occur through various factors during a workout but is not a direct outcome of lactic acid buildup itself.