A very popular form of ab exercise is the bicycle. This exercise works your upper, middle, and lower abs as well as your oblique muscles. It is performed by laying flat on your back then raising your head about six inches off of the floor. You want to place your arms in the same position as you would for a sit-up. Next, make a bicycle motion with your legs, ensuring they are as close to the ground as possible without actually touching the ground. If these are too difficult, a good way to make them slightly easier is to let your head rest on the floor; another way to decrease intensity is to raise your legs higher into the air. The higher you raise your legs, the easier it will be. I would encourage you to do this at the most difficult level you are capable of to push yourself to your limit.
For girls who want a slimmer waist line and not necessarily strong six pack abs, do the bicycle where it is not too hard but after about 20 seconds you feel the burn. This will both serve as a slight cardio exercise as well as a calorie burning movement that firms your abs, but does not cause major muscle building.
Another fantastic ab exercise is the hanging leg raise. If you are just beginning I would recommend starting these on a knee raise machine (which has a big half ball on the back and then two almost horizontal handles where you can rest your forearms.) To start you want to bring your legs up so that the upper part of your leg is parallel with the floor. You also want a ninety degree angle at the knee. Then you lower your legs straight down until they are free hanging, and then repeat the movement. A variation of this is to instead of raising your legs straight up, raise them to either side of your body, this focuses on the obliques while still maintaining good contraction on your main abdominal muscles.
For those of you who are more advanced, try doing the same exercise hanging straight from a bar. There is no back rest so the exercise will test how much ab strength you actually have and good form is key, otherwise you will be hanging from the bar swinging back and forth. Another good way to increase difficulty is to bring your legs up straight, instead of bent at the knee, until they are parallel with the floor; and to get even harder, bring your legs up straight all the way until they are perpendicular with the floor.
On all of the hanging exercises, make sure not to swing. This creates a momentum boost and will greatly decrease the effectiveness of your workout. Next time I will look at a few more abdominal exercises and then next week I will provide some good workouts for beginners, those who have been working out for a while, and those who are in great physical shape.