The abdominal muscles are usually the weak link in anyone’s “core” development. While endless sets of crunches and leg raise will strengthen the anterior abdominal wall,¹ these exercises provide a less direct activation pattern to the muscles living on the side of the waist (yes, the ones that seem to be so easily covered with extra calories). These side muscles, the obliques, are strongly activated during twisting functions, as well as straight trunk flexion. The kettlebell twist is an extremely effective core exercise because it targets the twisting functions of the oblique muscles.

Almost any sport that involves cross-body twisting and/or throwing motions, such as tennis, golf, swimming, softball or cross-country skiing,^2,3,4 goes better with stronger and firmer obliques. But even if you are just looking to firm up the sides of your waist, the kettlebell twist will help you reach your goals faster than you thought possible.

Primary Muscles Activated

The external oblique is the largest and most superficial of the lateral abdominal muscles.⁵ It is anchored from the fifth through the 12^th ribs by small bundles of muscle fibers. These bundles are intermingled with the serratus anterior muscle of the upper rib cage, and the latissimus dorsi muscle of the upper and middle back. The muscle fibers of the external oblique run from lateral to medial and superior to inferior, in the same direction that your fingers would point, if you were to put your hands in the pockets of your slacks. As the external oblique extends towards the center of your abdomen, it unites to form a flat, fan-shaped muscle. This muscle inserts into the pubic and iliac bones of the pelvis and hip, respectively.⁵ When both left and rights sides of the external oblique muscles work together, they can act to flex the trunk and move the head towards the feet. When one side contracts (e.g., the right external oblique), the body twists to that side (i.e., twists to the right side).

The internal oblique is another important muscle that lies just deep to the external oblique. It begins from a thick connective tissue sheath located in the lower back, called the thoracolumbar fascia, and from the iliac bone of the hip.⁵ Its fibers run at right angles to the external oblique muscle, fanning out from their origins and running towards the head (superiorly). They run approximately in the direction that your thumb would lie if you placed your four fingers in the front pockets of your pants, but left the thumb outside the pockets. The internal oblique inserts into the lowest three or four ribs, where they become continuous with the internal intercostal muscles (respiratory muscles of the rib cage). In contrast to the function of the external oblique, the internal oblique will twist the body towards the right if only the right side contracts, and towards the left if only the left side of this muscle contracts.⁵ However, similar to the external oblique muscle, the internal oblique will flex the trunk at the waist and move the head towards the feet, if both left and right portions of the internal oblique contract together.

Kettlebell Twist

1. Stand upright, with your feet about shoulder-width apart for good balance.

2. Hold one kettlebell in front of your chest with both hands. Lift your elbows out to the sides at shoulder height, with your palms pronated (towards your torso). Pull the handles of the kettlebell as if it were your goal to pull the handles apart. This will keep tension in your upper body as a secondary activator of back, shoulder, and triceps muscles.

3. Keep your hips pointed forward. Take a breath, then begin to exhale as you rotate your torso, shoulders, and head to the left as far as you can (do not twist your neck but keep your chin over the sternum and make sure that the twist is from your waist). Keep the elbows and upper arms at shoulder height throughout the twist.

4. After twisting as far as you can in one direction (remember: do not let your hips twist), inhale as you twist back to the center.

5. Continue, and now exhale as you twist to the right as far as possible. Continue the sequence of twisting to one side, then the other, and complete 12–15 twists on each side before taking a short break.

You should avoid holding your breath during the exercise, as this would increase intra-abdominal pressure and prevent the oblique muscle fibers from fully shortening during each twist. It is better to take a breath and then exhale as you are twisting to each side. The exercise is rather like squeezing a sponge out each time you twist to one side.

If you participate in weekend sports, you might occasionally experience pain in the lateral abdominal wall, and this might be an indication of micro tears resulting from straining the oblique muscles. This can occur by sudden and forceful twists, quick lateral flexion or sudden stretches that are often a part of many sports like softball, tennis and soccer, to name a few. Tearing of the internal oblique muscle from the undersurface of one of the lower four ribs or costal cartilages causes side strain injury.⁶ This is a painful condition, but the good news is that if your weekend activities involve sports that would be prone to side injuries, then these can be drastically reduced by strengthening the oblique muscles with kettlebell twists. And if your goal is to tighten and replace a soft waist with a firm one, while strengthening your core, then the kettlebell twist will become a new favorite exercise that will complement your healthy eating, cardio and exercise program to achieve that goal.

References:

1. Sternlicht E, Rugg S, Fujii LL et al: Electromyographic comparison of a stability ball crunch with a traditional crunch. J Strength Cond Res 2007;21:506-509.

2. Chow JW, Shim JH, Lim YT: Lower trunk muscle activity during the tennis serve. J Sci Med Sport 2003;6:512-518.

3. Irshad K, Feldman LS, Lavoie C et al: Operative management of hockey groin syndrome: 12 years of experience in National Hockey League players. Surgery 2001;130:759-764.

4. Kaneda K, Sato D, Wakabayashi H et al: EMG activity of hip and trunk muscles during deep-water running. J Electromyogr Kinesiol 2009;19:1064-1070.

5. Moore KL, and Daley AF. Clinically Oriented Anatomy. Lippincott Williams & Williams, Baltimore, 4th Edition pp. 1999. 178-187.

6. Stevens KJ, Crain JM, Akizuki KH et al: Imaging and ultrasound-guided steroid injection of internal oblique muscle strains in baseball pitchers. Am J Sports Med 2010;38:581-585.