That isn't what is measured though. The study measured for a change in fat burning by addition of anthocyanins into the diet, not whether fit people burn more fat. It is not useless to untrained people because these effects in trained people are a measure of the effects of blueberries for fat oxidation during exercise, so untrained people would theoretically have greater benefit from exercise by adding anthocyanins into their diet.

Your other reply isn't visible to me in the comments.

I'm not sure what is difficult to understand. Trained people burn more fat, yes. Untrained people burn less. So the experiment wants to see what eating blueberries does in regards to the fat burning effects of exercise. To remove the potential of beginner gains from skewing the results, use trained individuals to study the effects. The participants abstained from anthocyanins, and tested the fat oxidation. Then introduced anthocyanins, and tested again, showing an increase. Your point is irrelevant. The result of the study is that blueberries in the diet increase fat oxidation in response to exercise in humans. Like i said, if it showed effects in trained people, it would likely show effects in untrained people. There isn't some switch that just rejects anthocyanins because you aren't aerobically trained.

A small sample size isn't necessarily bad, it provides a stepping stone for the next group to investigate.

Edit: the authors of the study also declared the funders (blueberry company) basically didn't touch the study, and it is published in a peer reviewed journal.