Interesting study. I started out writing a study analysis, decided to put it as a response to this so the uninterested could skip it. You're welcome :-)

Mitochondria are fascinating. They essentially turn chemical energy into electrical, then use that to drive little motors that build ATP. Yeah, I was gobsmacked, too.

The best way I know to increase mitochondrial flux is extended level 2 exercise (max continuous exertion at which you can carry on a conversation). This looks to be another way. I wonder if they're synergistic - and whether this might also increase mitochondria in fat (adipose) cells, leading to 'beige' fat and increased metabolism. Pity they didn't also measure anything that might hint at changes there (e.g. body temp). I'd also have expected more efficient O2 usage, given the higher aerobic capacity that comes with increasing mitochondrial flux, but the ways to measure that are either expensive or unpleasant for the subject, or both.