1 · Acidosis during high-intensity effort
In maximal efforts the acid comes from H⁺ released by hydrolysis, not lactate, and above steady state it builds up and lowers pH, one fatigue mechanism among others.Maximal efforts of 10s-2min (400m, heavy sets) run mainly on glycolysis and the phosphagen system. First we have to dismantle an 80-year-old story: the acid does not come from lactate.H⁺ actually comes from hydrolysis — every time an ATP is split into ADP + Pi, a proton is released. Below steady state the mitochondria consume those protons for oxidative phosphorylation, so nothing accumulates; once intensity exceeds steady state and ATP is regenerated largely outside the mitochondria, H⁺ builds up and pH slides from 7.0 toward 6.5.
Lactate production does not cause acidosis — it retards it. Making lactate consumes H⁺ and hands back to glycolysis. Lactate coincides with acidosis because the same cellular conditions trigger both — it is a useful marker, not the cause. If muscle did not make lactate, acidosis and fatigue would arrive sooner.
Acidity is genuinely one fatigue mechanism: it inhibits phosphofructokinase, reduces Ca²⁺ release from the sarcoplasmic reticulum, and lowers myofilament Ca²⁺ sensitivity. But it is not the only one — inorganic phosphate (Pi) accumulation is also a major mechanism. Hold on to that, because it is what makes β-alanine's small but consistent effect size make sense later: it can only act on the H⁺ line.