Letters to the Editor Lactic Acid Still Remains the Real Cause of Exercise-Induced

To the Editor: We appreciate the article of Robergs et al. (5), which gives a complete overview of the biochemistry of metabolic acidosis originating from intense muscular exercise. However, with the intention to clarify the causes of the pH decrease, the authors try to prove that lactic acid plays no role in this process and thus declare that generations of exercise physiologists have been using a false concept. We feel that this attempt results in confusion. A number of statements cannot be accepted: Source of Increasing Pi in Exercising Muscles “...the origin of accumulating intramuscular Pi is ATP hydrolysis, not creatine phosphate breakdown, which is still mistakenly interpreted by many physiologists. ” (p. R509) As known from numerous studies, creatine phosphate (CrP) concentration in hard-working muscle is massively reduced while changes in [ATP] are only small. Binding of Pi to the latter is a transitory step only. Consequently, CrP breakdown is the real and the most important source of accumulating Pi. Amount of Proton Release During Glycolysis Most problematic is the calculation of the balance of proton release provided by Robergs et al. (5). Equations 1 and 2 ending with pyruvate show that glycolysis produces 2 H or 1 H starting with glucose or glycogen, respectively: glucose 2 ADP 2Pi 2 NAD3 2 pyruvat