Final answer:
Recent research has revised the traditional view that lactic acid buildup is the main cause of muscle fatigue. Now, it's understood to be more complex, involving lactic acid as one of many contributing factors. Elevated lactic acid is a part of the body's response to high-intensity activity, with muscle fatigue being influenced by both physiological and psychological factors.
Step-by-step explanation:
Current research about lactic acid suggests that lactic acid builds up during strenuous activity due to anaerobic glycolysis and can contribute to muscle fatigue by lowering intracellular pH, thus affecting enzyme and protein activity. However, elevated lactic acid levels alone are not solely responsible for muscle fatigue. Fatigue in muscles is multifactorial and includes aspects such as energy availability, oxygen delivery, and psychological factors.
The traditional view that lactic acid accumulation contributes to muscle soreness and stiffness has been challenged by more recent research. Lactate is removed from muscles into the blood circulation and used by the liver for metabolism. This process may not be the primary cause of muscle fatigue, according to newer perspectives which highlight the complexity of factors involved in muscle fatigue and performance.