Despite the exercise industry's frequent creation of new ab-exercise gadgets, one of the most effective ways to train the abdominal muscles is with the crunch. The "Encyclopedia of Bodybuilding" explored the exercise routines of the world's most famous bodybuilders and found that at the core of their ab routines is the crunch. But knees-in-the-air crunches must be performed with proper form and intensity if you want to get the best results.
How to Perform
Lie back on an exercise mat. Bend your knees and lift your feet until your thighs are perpendicular with the floor. Cross your arms over your chest, or place your fingertips behind your ears to get a better stretch in your abdominal muscles. Roll your shoulder blades off the ground, tilting your ribcage towards your hips. Contract your abdominal muscles hard for two seconds. You can either lower your shoulder blades back to the ground or not quite to the ground to maintain tension in your abdominal muscles.
Muscles Used
Crunches with the feet and knees elevated do an effective job of isolating the rectus abdominis and the external obliques. The rectus abdominis is the wall of muscle that runs from the lower ribcage to the pelvis and, when developed, creates the six-pack look. The external obliques connect to each side of the ribcage and to the center of the pelvis. Although they are responsible for twisting the body and tilting it from side to side, they also aid the rectus abdominis in crunching the ribs and pelvis straight towards each other. Compared to the situp, hip flexor involvement is less during knees-in-the-air crunches, but the rectus femoris head of the quadriceps and the tensor fasciae latae do work to hold your legs up.
Advantages
Knees-in-the-air crunches have a number of advantages over other abdominal exercises. Unlike in situps, the abs work far harder than the hips. With the feet in the air, it's impossible to lift the lower back from the ground, making it much safer for the spine. The simplicity of the exercise is also an advantage. It allows you to focus on hard contractions instead of a lot of movement. This is why the crunch is still the core of the routines of some of the most muscular people on earth, including eight-time Mr. Olympia Arnold Schwarzenegger, according to "The New Encyclopedia of Modern Bodybuilding." His tiny waist and well-defined abs, molded largely with crunches, made the rest of his body that much more impressive. As you gain better control over your muscle groups, crunches develop with you, since the harder you crunch, the better results you'll see.
Variations
Variations on the knee-in-the-air crunches can be worked into your routine to keep your body guessing. Many people can feel the exercise better in their upper abs than the lower abs. Positioning your thighs less than perpendicular to the ground will increase lower abdominal activity, as will pumping your feet in and out. However, this will also increase the involvement of the anterior hip flexors. To minimize involvement of the front hip flexors and allow full concentration on the abdominal muscles, place your feet on a bench. Although the intensity of the crunch is primarily influenced by how hard you contract, you can also increase the resistance by holding a weight plate against your chest.
References
- "The New Encyclopedia of Modern Bodybuilding"; Arnold Schwarzenegger; 1998
- "Strength Training Anatomy, 3rd Ed."; Frederic Delavier; 2010
- "Encyclopedia of Bodybuilding"; Robert Kennedy; 2008
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