When I follow the normal routine of my gym including stretching after the workout, I strongly feel a shortening of my lower back muscle, to the point where I have a distinct hollow back after working out.
I don't know the english name of the exercise for the lower back, but basically I lie on a platform inclined at roughly 45°, tilt my torso downward till the angle torso-legs is 90° or a bit smaller, and up again. I do (as advised) 15 reps, 3 sets, that's barely doable for me.
I concentrate strongly on my lower back when stretching after exercise, doing stuff I've seen in yoga or pilates, but I still have a stronger hollow back after a workout (or at least it feels like that).
Why is this so? Any advices to avoid long term trouble?
edited to add/clarify: My subjective feeling is that the lower back muscles are shorter (and don't have that feeling that strongly with other muscle) and I see that it affects my posture.