High impact exercise reverses damage to mitochondia?

[PoetInSF]

Now, once I've built up a sort-of moderate baseline, I sometimes will do things that I feel are outside of what I technically should be doing (like I will full-out RUN a block or two hard-ish, then walk a few blocks). It is sort of amazing, that it does feel good in a way.

After a 100m run (more like jogging actually) and 5 min rest, it does feel good indeed. But feeling good and improving are not necessarily the same thing. I've been walking for 3 years, even when I was pretty sick, because it makes me feel better and sleep well at night. But I'm not convinced that all that walking is the reason that I'm improving, for the progress has been way too slow. And I'm coming to the same conclusion about running too. I still think the exercise is only helping the healing, not causing it. And we are probably lucky cases that exercise does help.