Knee ups are an advanced exercise for your abdominal muscles. You hang from a bar or dip machine and pull your knees up toward your chest. This is a type of reverse crunch -- you pull your legs toward your chest instead of crunching your torso toward your legs. You can substitute knee ups with other reverse crunch variations.
Function
Lifters do reverse crunches to work their lower abs versus upper abs. Although several bands of connective tissue called tendinous inscriptions divide the rectus abdominis into upper and lower parts, you cannot contract one part independent of the other part. The entire abdominal sheath contracts as one unit. However, stabilizing the torso and lifting your legs toward your chest results in more shortening in the lower part of the abdominal wall.
Standard Reverse Crunch
During the knee up exercise, you lift your legs directly against gravity. The standard reverse crunch is less challenging than a knee up because you are lying on the floor. Start with your knees at a 90-degree angle and your thighs perpendicular to the floor. Your knees should be stacked over your hips. Exhale and pull your knees toward your chest, bringing your hips off the floor. When you lower your legs, do not lower them to the floor. Return your legs to the starting position.
Stability Ball Knee Tucks
This is a more challenging reverse crunch because you are on an unstable ball. Lie on your stomach over a stability ball. Walk your hands forward until your knees are on top of the ball. Make sure you are a straight line from your shoulders to your ankles. Your wrists should be directly below your shoulders. Exhale and pull your knees toward your chest, rolling the ball under you. Continue pulling in until your shins are resting on the ball and your knees are under your hips.
Seated Leg Tucks
This exercise is similar to the knee up in that you pull your legs up against gravity. However, it is less challenging because you angle your body instead of being vertical to the floor. Sit on the edge of a bench and place your hands behind you. Lean your torso back slightly. Pull your feet off the floor. This is the starting position. Exhale and pull your knees to your chest, allowing your lower back to round.
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