Sports practice and athletic training are subject to permanent evolution, and it's no wonder that traditionally effective sit ups are not recognized as generally valid anymore. The essential move of the sit ups used to be the lifting of the torso from the lying position towards the bended knees. At present, the lift is done only partly with a tightening of the abdominal muscles and almost no bending towards the knees. There are a few tricks to effective sit ups that you should be aware of.
First of all, the body position is very important. There is a common risk to strain the neck muscles instead of tightening the abdomen. No effort should affect the head during the move. This is in fact the whole purpose of the laced fingers behind the head: to support the movement and allow only for the abdomen muscles to take over the effort. The distance between the body and the floor during the lift should not be higher than eight inches. If you work out at the gym, the coach should teach you how to do effective sit ups, but if you train at home, it is important to read a few materials before taking up the exercises.
Anyone can appreciate how effective sit ups are by noticing the adaptation of the body to the training conditions. If sit ups seem difficult to perform at first, the more you practice, the easier it gets. Do not increase the difficulty level immediately or rapidly. If you train with regular sit ups for one or two weeks, all you have to do is just to increase the number of reps per week, then, you can think of another difficulty element to include in the routine. A Swiss ball can allow you to perform more difficult but highly effective sit ups too.
Lie on the ball with the lower back and keep the torso parallel with the floor. The feet should keep you balanced during the exercise. If you are horizontal on the exercise ball, put your hands behind the head and lift the torso for a few inches. To maximize the effort in these effective sit ups, you can lower the body a bit under the horizontal line so that the abs have to work more to lift you up. Regardless of the position of the legs during the exercises, it is highly important that you don't work too hard for the lower back. It is false to judge effective sit ups by the way they push the body limits and cause pain, since a certain comfort level has to remain permanent.