# Cable Lying Alternating Bent Leg Jackknife - Canonical: https://fitwill.app/exercise/11262/cable-lying-alternating-bent-leg-jackknife/ - Media ID: 11262 - Primary muscle: Abs - Body part: Core - Equipment: Cable Machine - Video: https://fitwill.app/videos/11262/cable-lying-alternating-bent-leg-jackknife.mp4 ## Description The Cable Lying Alternating Bent Leg Jackknife is a floor-based core exercise performed with a cable machine set to its lowest pulley. You lie on your back with your head toward the machine, hold one handle in each hand with your arms extended overhead along the floor, and then alternate pulling one handle up and over your head while driving the opposite knee in toward your chest. Because the cable provides steady resistance through the entire range of motion, your abdominals stay under tension even at the stretched position where bodyweight-only crunches tend to go slack. This movement works the rectus abdominis as the prime mover, with heavy involvement from the lower abs and hip flexors as each knee drives toward the torso. Since the arm and leg on opposite sides move together, the obliques also work to keep your ribcage and pelvis coordinated through the cross-body pattern. That combination makes it more demanding than a standard floor crunch, and it trains your midsection in a way that closely resembles how the core works during walking, running, and climbing. The setup matters more than people expect. Lying far enough from the machine so your arms rest fully overhead with light tension on the cable puts the abs in a lengthened starting position, which is where most floor ab work falls short. If you drift too close, the handles lose tension and the hardest part of each rep disappears; too far away and the cable drags you out of position before you even start moving. To execute it well, keep your lower back in contact with the floor throughout, move one arm and the opposite leg together with a deliberate crunch rather than a rushed fling, and pause briefly at the top of each rep. The extended leg should stay hovering just above the floor rather than resting, so the working side never gets a full break. This exercise suits lifters who already handle basic crunches and leg raises and want added resistance, as well as anyone training the core with a machine-only setup or returning from time away from the gym. It fits well at the end of a workout as a focused abdominal finisher, typically for sets of 8 to 12 reps per side. For safety, keep the weight modest at first, since the overhead position and simultaneous leg drive can pull your ribs up and arch your lower back if the load is too heavy. Move slowly, keep your head neutral, and stop the set as soon as your lower back starts lifting off the floor. ## Instructions 1. Attach a single handle to each side of the cable at the lowest pulley setting and select a light weight to start. 2. Lie on your back on the floor with your head toward the machine, reaching overhead to grip one handle in each hand, arms extended along the floor above your head. 3. Walk your body away from the machine until you feel light tension on the cable with your arms fully overhead, and extend both legs straight along the floor. 4. Brace your core gently and press your lower back toward the floor before starting the first rep. 5. Exhale and pull the right handle up and over your head toward the ceiling while simultaneously bending your left knee and drawing it in toward your chest, curling your upper back off the floor. 6. Pause briefly at the top, feeling the crunch through your abdominals as the elbow and knee converge. 7. Lower the handle back overhead and extend the left leg back out with control, keeping it hovering just above the floor rather than resting. 8. Repeat on the other side, pulling the left handle as the right knee drives in, and continue alternating for the desired number of reps per side. 9. Breathe out on each crunch and in as you return to the extended position, keeping the movement smooth rather than rushed. ## Tips & Tricks - The most common mistake is losing cable tension by sliding toward the machine between reps. Mark your spot on the floor or keep your arms locked out overhead so every rep starts from the same stretched position. - If your lower back arches as the leg extends, do not lower the extended leg all the way to the floor. Hover it slightly higher and shorten the range until you can keep your pelvis stable. - Avoid turning this into an arm exercise. The handle should follow because your torso curls, not because your biceps and shoulders are yanking the cable down. - Keep the bent knee driving toward your chest rather than out to the side. Letting the knee flare turns the rep into a hip rotation and reduces the abdominal work. - Start with a lighter weight than you would use for cable crunches seated or kneeling. The overhead position puts your shoulders and abs at a mechanical disadvantage. - Move your head with your torso instead of jutting your chin forward. Tucking the chin slightly as you crunch keeps the work on the abs and your neck comfortable. - If the handles are hard to reach from a lying position, have the cable set before you lie down and grip both handles before extending your legs, rather than adjusting mid-set. - Control the return as much as the pull. Letting the cable snap your arm back overhead removes the loaded stretch, which is one of the main reasons to use this variation. ## Frequently Asked Questions ### What muscles does the Cable Lying Alternating Bent Leg Jackknife work? The rectus abdominis does most of the work, with strong support from the lower abs and hip flexors as each knee drives toward the chest. The obliques contribute because each rep crosses the midline with an opposite arm and leg. ### Why lie on the floor instead of doing this on a bench? The floor gives your lower back a stable reference point and lets you feel when it starts to arch. It also lets you set up directly in line with the low pulley so the cable pulls along the floor over your head. ### Is the Cable Lying Alternating Bent Leg Jackknife suitable for beginners? It can be, but only with a very light weight and a shorter range. Beginners are usually better served mastering bodyweight crunches and single-leg raises first, since coordinating the opposite arm and leg adds a timing challenge. ### How far from the cable machine should I position myself? Lie far enough away that your arms are fully overhead with light, even tension on both handles before you start. If the cable slackens at the stretched position, scoot back; if it drags you, move closer. ### Should both legs stay off the floor during the exercise? The working leg is bent and driving toward the chest while the extended leg hovers just above the floor. Letting the extended leg rest between reps turns the set into single, disconnected reps instead of continuous tension. ### What is the most common mistake with this movement? Pulling mostly with the arm instead of curling the torso. If your upper back barely leaves the floor and your elbow does all the traveling, reduce the weight and focus on crunching the ribs toward the pelvis. ### What can I substitute if my gym has no dual low pulleys? A bodyweight alternating bent leg jackknife on a mat works the same pattern with no equipment, and a single-handle cable crunch with a knee drive on one side at a time covers similar ground. ### How many reps should I do per side? Eight to twelve controlled reps per side is a practical range. Because the cable keeps tension on the abs even at full stretch, moderate reps with a deliberate pause usually beat high-rep rushing. ### Is it safe for the lower back? With a light weight and your lower back kept in contact with the floor, it is generally well tolerated. If your back arches or lifts during the rep, stop the set, reduce the load, and hover the extended leg higher. ### Where should this exercise fit in my workout? It works best near the end of a session as a dedicated abdominal finisher, after your main compound lifts. Placing it first would fatigue the core and compromise bracing on heavier exercises like squats or deadlifts.