Knife Sit-Up
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The Knife Sit-Up is a bodyweight strength exercise where you lie on your back, extend your arms overhead, and perform a sit-up while reaching one hand toward the opposite foot in a "knife-like" slicing motion, then alternate sides. Its primary purpose is to intensify abdominal engagement and hip flexor activation for enhanced core strength and rotational power. It benefits athletes, fighters, and anyone seeking advanced abs training beyond standard crunches, requiring no equipment.
How to Perform Knife Sit-Up
- 1Lie on your back on the floor with knees bent at 90 degrees and feet flat on the ground, hip-width apart.
- 2Extend both arms straight overhead toward the ceiling, keeping them close to your ears with palms facing forward.
- 3Engage your core by pressing your lower back into the floor.
- 4Inhale to prepare, then exhale as you simultaneously curl your upper body off the floor and reach your hands forward toward your knees in a "knife-like" slicing motion.
- 5Continue curling up until your torso is perpendicular to the floor and your hands reach as close as possible to your shins without rounding your lower back.
- 6Inhale as you slowly lower your torso back down with control, keeping arms extended overhead.
- 7Repeat for desired reps, maintaining constant core tension.
- 8Key form tips: Keep your lower back pressed into the floor throughout to avoid strain—do not let it arch. Move slowly to prevent momentum; focus on hip flexor and ab contraction, not neck pulling. Common mistakes: Jerking up too fast, lifting feet off the ground, or hyperextending the neck.
