The V-up, sometimes referred to as a jackknife crunch, is a dynamic and challenging bodyweight exercise. This advanced movement requires significant abdominal strength and coordination, making it a step up from foundational exercises like the standard crunch. Performing the V-up correctly involves simultaneously raising the upper torso and the legs, meeting the hands to the feet to form a distinct “V” shape with the body. This article explores the specific muscles targeted, details the proper technique, and outlines how to best integrate this exercise into a fitness regimen.
The Core Muscles Activated by V-Ups
The primary muscle targeted by the V-up is the rectus abdominis, the long, flat muscle that runs vertically along the front of the abdomen and is responsible for spinal flexion. This muscle works intensely to bring the ribcage and the pelvis closer together during the upward phase of the movement. Because the exercise requires lifting both the upper body and the lower body simultaneously, it places a demanding load across the entire length of the rectus abdominis, promoting greater muscle recruitment than simple crunches.
The oblique muscles also play a significant role. Their main function during the V-up is to stabilize the trunk and prevent unwanted rotation or tilting as the body balances on the glutes and lower back at the peak of the contraction. This stabilization demand makes the V-up a compound core movement, requiring synchronized effort from multiple muscle groups for balance and control.
Lifting the legs off the floor against gravity necessitates the strong involvement of the hip flexors. While the hip flexors are unavoidable in this movement, the goal is for the abdominal muscles to initiate and control the spinal flexion portion of the exercise, rather than allowing the hip flexors to dominate the lift. The simultaneous movement of the upper and lower body makes the V-up highly effective, demanding a level of strength and coordination often found lacking in less challenging core exercises.
Achieving Proper V-Up Form
Begin the V-up by lying supine on the floor with the legs extended straight and the arms stretched overhead, aiming to keep the lower back in slight contact with the ground. This starting position creates a long lever, increasing the challenge by maximizing the distance the limbs must travel. Engaging the core before movement begins helps to maintain a neutral spine and protects the lower back from strain.
The movement is initiated by a controlled, simultaneous lift of the torso and the legs, striving to touch the hands to the shins or feet at the apex of the movement. Exhale sharply during this concentric (lifting) phase, as this helps to forcefully contract the abdominal muscles and further stabilize the trunk. At the top, the body should resemble the letter “V,” balanced momentarily on the tailbone or glutes.
The descent, or eccentric phase, is arguably the most important part of the exercise for building strength and should be performed slowly and with absolute control. Inhale gently as the body slowly lowers back to the starting position, resisting the urge to simply drop the limbs to the floor. Rushing the repetition or allowing momentum to dictate the lift is a common error that drastically reduces the muscle-building effectiveness of the V-up.
Another frequent mistake is allowing the lower back to arch excessively when the legs are lowered or during the initial lift, which can place undue stress on the lumbar spine. If maintaining straight legs causes the lower back to lift off the floor, form must be prioritized over range of motion, which may mean not lowering the legs all the way or bending the knees slightly. The movement must be powered by the abdominal wall, not by a forceful swing of the arms or legs.
Incorporating V-Ups into Your Routine
V-ups are an intense exercise, and performing them two to three times per week allows for adequate recovery and muscle adaptation. For those new to the movement, quality of form should be prioritized over the quantity of repetitions, focusing on control throughout the entire range of motion. A typical recommendation for building strength is to aim for two to four sets of 10 to 15 repetitions, though beginners may start with a lower number.
If the full V-up is too difficult initially, one effective modification is the bent-knee V-up, or tuck-up, where the knees are drawn toward the chest instead of keeping the legs straight. This shortens the lever, reducing the demand on the hip flexors and making it easier to maintain proper spinal alignment. Alternating single-leg V-ups, where only one leg is lifted at a time, is another way to scale the difficulty while still challenging the core and obliques.
When three sets of 15 repetitions are comfortable, progressions can be introduced to increase the challenge. These include performing the repetitions with a slower eccentric phase to maximize time under tension, or incorporating a static hold at the top of the “V” for a few seconds to build isometric strength. Weighted V-ups, performed by holding a light dumbbell or medicine ball, can further increase resistance for advanced users. V-ups complement other core exercises, such as planks for isometric endurance and rotational movements for oblique development.