The science behind how it happens is not simple and most people simply don’t understand the details behind the mechanics of what happens during prolonged levels of very high contributions from anaerobic glycolysis. There’s a couple of ways that mitochondrial destruction can happen.
First, calcium begins to accumulate as long as H ions are causing the electrochemical potential to stay negative and this accumulation is followed by water intake down the osmotic gradient, leading to swelling and stretching of the inner membrane. This can cause a chain of events that leads to rupture and activation signals that cause cell death.
Second, high ROS concentrations can also change the membrane permeability and lead to leakage of cytochrome C into the cytosol. This interacts with APAP-1 to form dATP. Deoxygenated adenosine triphosphate, which begins another cascade that leads to cellular aptosis as well.
There’s some Russian textbooks by a guy named Seluyanov that discuss their research and changes in mitochondrial density following various types of training and they give some specifics as well. I’ll see if I can dig some of it up, but you will certainly have to look around pretty deep into the science to get to the details of how it happens, but yes, it does happen and whoever tells you differently hasn’t done their homework.