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This or That: Crunches vs. Leg Raises

By Devin Wicks

Welcome to "This or That?", a weekly series in which I help demystify the different exercises you can do in the gym. There are many familiar exercises that seem very similar—but which should you do to accomplish what result? In this series, I'll try to give some answers. Ab exercises offer a dizzying array of possibilities, but how many of us really know which exercises do what? Today I'd like to give you two different exercises that cover the full range of your ab muscles. So, let's compare the classic crunch with leg raises. Here we go:

Floor Crunches
Lie on your back with your hands behind your head and feet in the air so your thighs are vertical. Keeping your chin off your chest and elbows wide, exhale and lift your shoulders off the ground, leading with your sternum bone. Note that I am not describing the version of the exercise where you keep your feet on the floor as you lift. That version leads many people to push off the floor with their feet. For true muscle isolation, try the feet-in-the-air version.

Seems familiar. So here's what it does (and doesn't):

  1. Work the major upper ab muscle: The rectus abdominis is the large, paired, central muscle forming the surface of your abs. It is thickest at the top, where this exercise targets. (The entire muscle is your "six-pack".) It is the primary muscle worked with this exercise, but you can add the transversus abdominis by drawing your bellybutton in toward your spine as you perform the crunch. The transversus abdominis is the horizontal girdle of deeper muscle running across your lower abdomen, below your belly button. Engaging this muscle will give you a much deeper contraction and will aid in developing important posture muscles.
  2. Variations: This is a simple exercise, but small changes in position will shift the workload to different muscles. For a variation, add intensity by drawing your knees in toward you as you crunch upward. If you alternate bringing your right elbow to your left knee and then your left elbow to your right knee as you perform the crunches, you will help develop your obliques. These are the muscles along your sides, above your hips, and help to give your abs definition and strength in turning motions.
Crunches are the most basic ab exercise there is. But you absolutely must mix them up with other kinds of exercises or you cannot develop true functional strength. By isolating the rectus abdominis and to a lesser extent the transversus abdominis, crunches don't give you a full development of your ab muscles. One option for variation is the incline leg raise.

Floor Leg Raises
Lie face up on the floor with your hands behind your head. Bring your body up in crunch position and hold at the top. Keeping your legs straight, draw your bellybutton in toward your spin as you exhale and begin raising your legs. Curl your tailbone under and roll up the spine as though you were trying to bring your knees to your head. Slowly return to the start position.

Here are the benefits of leg raises:
  1. Lower ab-intensive: In this exercise, you begin by working the quadriceps (iliopsoas, tensor fascia lata and the rectus femoris) during the initial phase of the movement. But as you begin rolling up the spine you increase the intensity on the abdominal core and contract mainly the infraumbilical (lower abs) portion of the rectus abdominis, rather than the upper portion as in a crunch. You can also increase the intensity on the transversus abdominis by drawing your belly button into your spine as you perform the movement..
  2. Intensity variations: You can really up the intensity on this exercise by taking away the floor's leverage. Try doing them lying on a flat bench with your legs (though not your hips) hanging off the end. Grab the grips behind your head for stability. Now, perform the leg lifts just as you would otherwise, lifting the legs up over your head from your center. Lower back down only to horizontal in between lifts.
Let's sum up: The crunch is basic to any ab workout, but should be used in multiple variations to diversify the exertion, and in the context of a wide assortment of core and ab exercises. One such other exercise is the leg raise, which helps to target the typically weaker lower abs.

About Devin Wicks: Devin Wicks (ACSM-HFI, USAW Club Coach) is creator of the RealJock Strength Foundation 12-Week Workout program and the fitness operations director at the University of California, Berkeley, where he acts as specialty strength coach for some of the university's premier sports teams, and is coordinating a pioneering new campus employee wellness program.