Bill, I first learned of mitochondrial damage here when Pavel and Al discussed the implications in an earlier thread. It isn't an issue wildly known, I think, and in fact, paraphrasing Pavel here, that a Russian scientist wasn't taken very seriously when the effects of glycolytic training impacted strength and was pushed aside. It is in part I think to do with the whole sports conditioning model of strength and conditioning....training the glycolytic pathways has upsides and downsides and its damaging effect on mitochondria absolutely a downside if you have worked so hard to gain strength. It is really dependent on if you and your sport needs the conditioning effects of glycolysis, or lactate threshold training. And if so the sessions need to be brief, pre-competition and to be left alone during the season as your sport will provide the conditioning it needs. And if you have a strong strength and aerobic base to start with, then the effects will be reduced compared to someone who is de or untrained. So push, push, push all the time, something has to give. Slow and steady training with a little dip into glycolysis now and then but not too much. This may help, it is running biased but:
So Long runs can be used to increase mitochondria in some FT fibers. While a variety of paces does need to be used, too much faster paced running above the Lactate Threshold can actually damage mitochondria. Some studies have shown that after high acidosis training sessions, mitochondria have been damaged beyond repair. High acidosis training includes hard sessions that lower the pH of the muscle. These are intense sessions that are above the Lactate Threshold. In my training session, both VO2max and anaerobic work such as Lactate Tolerance work can be considered high acidosis training. That's why this type of training should be used only so often and plenty of rest given afterwords for tissue repair.
from:http://magstraining.tripod.com/Physiology.html#Increase_in_size_and_number_of
I've learnt a great deal here on this forum that have changed a lot of my views and S&S - with its A&A conditioning focus - has been the biggest game changer for me.