Original:   In 2004, Robergs et al. maintained that lactic acidosis during exercise is a "construct" or myth, pointing out that part of the H+ comes from ATP hydrolysis (ATP4 + H2O ADP3 + + H+), and that reducing pyruvate to lactate (pyruvate + NADH + H+ lactate + NAD+) actually consumes H+.
Revised:  Some causes of this are metabolism in red blood cells that lack mitochondria, and limitations resulting from the enzyme activity that occurs in muscle fibers having high glycolytic capacity. In 2004, Robergs et al. maintained that lactic acidosis during exercise is a "construct" or myth, pointing out that part of the H+ comes from ATP hydrolysis (ATP4 + H2O ADP3 + + H+), and that reducing pyruvate to lactate (pyruvate + NADH + H+ lactate + NAD+) actually consumes H+.
Edit intent: meaning-changed