I think I'm going to be careful with the superman one, because in the back exercise class we were introduced to one that I think stretches the lower back in a similar way -- looking at English sites that one is called "Sphinx pose", but I find that quite uncomfortable. It doesn't cause me an alarming pain or anything like that, that would make me break off a movement, but it doesn't feel good either, like for example stretching my back in the other direction, i.e. really making it round, like in that position that yoga calls "child pose" for example, does. Though the superman/locust one seems to bend the back less, so maybe it is worth a try to see how that one feels.