The waste product traditionally believed to build up in muscles causing soreness and fatigue is lactic acid. It is produced during anaerobic metabolism when the body breaks down glucose without enough oxygen, such as during intense exercise
. However, modern research shows that lactic acid itself is not the direct cause of muscle soreness or fatigue. Lactic acid is quickly cleared from muscles and does not cause the delayed muscle soreness experienced after workouts, which is actually due to microtears in muscle fibers
. The sensation of muscle "burn" during intense exercise was once attributed to lactic acid buildup and the resulting acidosis (increased acidity), but this view has been challenged by more recent studies
. Other factors, such as the accumulation of inorganic phosphate and changes in ion concentrations (potassium, chloride), also contribute to muscle fatigue by interfering with muscle contraction processes
. Lactic acid may even have some protective or ergogenic effects during exercise rather than being purely detrimental
. In summary:
- The waste product linked to muscle fatigue and soreness is lactic acid (or more precisely, lactate and associated hydrogen ions)
- Lactic acid buildup causes temporary muscle acidity but is not the main cause of muscle soreness or long-term fatigue
- Muscle soreness after exercise is mainly due to microtears in muscle fibers, not lactic acid
- Other metabolites like inorganic phosphate and ion imbalances also play key roles in muscle fatigue
Thus, the name of the waste product commonly associated with muscle fatigue and soreness is lactic acid , though its role is more complex and less directly harmful than once thought.
