Final answer:
During hard exercise, lactic acid causes muscles to feel sore and fatigued as it builds up during lactic acid fermentation, which happens when muscles are deprived of oxygen. The enzyme lactate dehydrogenase facilitates this fermentation process, and though lactic acid was once blamed for soreness, current research offers different hypotheses about its role in muscle fatigue.
Step-by-step explanation:
Lactic acid, C₃H₆O₃, is what causes your muscles to feel sore and fatigued during hard exercise. During strenuous activities, such as running a race or lifting heavy weights, our muscles use lactic acid fermentation to produce ATP, which is necessary for muscle contraction when oxygen levels are insufficient. This process is facilitated by the enzyme lactate dehydrogenase (LDH). Lactic acid is a byproduct of this fermentation process, and its accumulation in the muscles has been associated with symptoms like stiffness, fatigue, and soreness.
The reaction involved in this fermentation is Pyruvic acid + NADH → lactic acid + NAD+, and lactate dehydrogenase catalyzes this process. Although the buildup of lactic acid was once widely believed to be the direct cause of muscle soreness, recent research suggests that it might be related to a decrease in internal pH leading to the activation of motor neurons, which could contribute to the sensation of muscle fatigue. Nevertheless, lactic acid is eventually removed from the muscles and transported to the liver, where it can be reconverted into pyruvic acid and used in further catabolism for energy.
Understanding the role of lactic acid in exercise is crucial for athletes and anyone engaged in physical activities to manage their performance and recovery effectively. It is a natural part of the body's response to oxygen deficiency in the muscles during intense exercise and is not harmful in the long term as the body clears lactate efficiently under normal conditions.