While this exercise does strengthen and build muscle in the obliques, it does so at a cost. Similar to the crunch, this movement places extra stress on the spine, which can lead to a plethora of injuries like a disc bulge. Instead try a unilateral kettlebell carry (holding a kettlebell in one hand with the arm extended). This move will strengthen your quadratus lumborum, your abdominal wall, obliques, back, and shoulders. It's extremely effective because it requires you to create tension in your muscles in order to maintain an upright position.
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