I have been training in flats (Nike Katana Racer) for quite a while and thinking about why they work so well for me. I hypothesize that they are better biomechanically not because of their weight but simply because their heel/toe drop is less than most trainers. Reviewing the history I find that I got injured with "flats" that have higher heels (Brooks ST, Asics Speedstar for example) and not with trainers and trail shoes that had pretty equal heel/toe cushioning (Brooks Epiphany for example). I'm a fore-to midfoot striker.
If this is correct then maybe it makes sense to train in a shoe that is more cushioned than a flat but avoids the "hig heel" effect.
Any thoughts on this?