Question

Why does lactic acid fermentation “kick in” during a sprint race?

Answer 1

because tissues become depleted of \(O_2\) (which functions as the last electron acceptor in the electron transport chain) and it cane transported fast enough, a "salvage" pathway to continue with glycolysis (so your cells have energy and don't die) is to reduce pyruvate to lactate (lactic acid) to regenerate \(NAD^+\).

Answer 2

it can't be transported**