I have noticed since I moved to India and sleep on the floor that my muscles relaxes much better. When I used to sleep in a soft bed the tension in the muscles from moving/working during the day, would still be there when I woke up, but I was so used to it that I didn´t notice. Not until I slept on a hard floor and the resistance made it nessecary for me to consciously let go of muscle tension. It is absolutetly impossible to sleep on hard surface if your body is tense, it hurts. It is like someone massages your muscles a bit hard, it hurts as long as you can´t relax them. I think that´s one of the reason why the people here has very flexible bodies even in old age in spite of malnutrition, they squat, they sleep on the ground/ floor and their body´s don´t get spoiled using to much furniture.