Unlike many core exercises, which focus primarily on the upper or lower abs, the V-Up engages the entire rectus abdominis and obliques. By lifting both your upper and lower body simultaneously, you create an intense contraction throughout your entire core. The V-Up, also known as a jackknife, is a full-body move that works your core, legs, back, and shoulders. The exercise works the upper and lower abs muscles simultaneously to build an impressive six-pack abs
