# Knee In And Out Crunch - Canonical: https://fitwill.app/exercise/7752/knee-in-and-out-crunch/ - Media ID: 7752 - Primary muscle: Abs - Body part: Core - Equipment: Body Weight - Video: https://fitwill.app/videos/7752/knee-in-and-out-crunch.mp4 ## Description The Knee In And Out Crunch is a floor-based body weight abdominal exercise that combines an upper-body crunch with a simultaneous knee tuck. You start lying flat on your back with legs extended and arms reaching overhead, then fold your torso and knees toward each other in one coordinated squeeze before extending back out to the long, open position. Because the top and bottom halves of your body move at the same time, the entire rectus abdominis works through a much longer range than in a standard crunch done from the floor with feet planted. This movement suits intermediate trainees who already own a solid basic crunch and a hollow-body hold. Beginners can still use it, but they will get more out of it after building control with simpler crunch variations, since keeping the low back quiet while both ends of the body move takes some coordination. It fits well into home workouts, core finishers, and circuit training because it needs nothing more than floor space and a mat if you want cushioning under your spine and tailbone. The primary work comes from the rectus abdominis, with strong involvement of the lower portion as you draw the knees in. The hip flexors assist every tuck, and the obliques stabilize your ribcage so the folding happens straight up and down rather than twisting. The arms stay extended and act as a counterweight, which means your shoulders and upper back work isometrically to keep them reaching throughout each rep. Setup matters more than speed here. Lie back with your low spine neutral, arms extended overhead but not touching the floor, and legs straight with heels hovering a few inches above the ground. If you start with your heels resting down, the first inch of the tuck loses tension; if you yank your arms or head forward, your neck does the work your abs should be doing. To execute the rep, exhale as you curl your shoulder blades off the floor while bending your knees and pulling them toward your chest, letting your hands sweep forward alongside your knees or shins at the top. Pause briefly in that tucked, rounded position, then reverse the motion under control: extend the legs back to the hovering straight-leg position as your arms travel back overhead and your torso lowers. Move slowly enough that your heels never slam down and your head never leads the curl. A few practical points keep this exercise productive. Keep the range honest rather than chasing height; a short, well-braced fold beats a jerky one every time. If your lower back arches off the floor as you extend your legs, bend your knees slightly more or keep your heels higher. Stop the set when you can no longer lift your shoulder blades cleanly, because rep quality in this movement drops off fast once fatigue sets in. ## Instructions 1. Lie flat on your back on an exercise mat with your legs straight and together, and extend both arms overhead behind you, palms facing up. 2. Lift your heels a few inches off the floor so your legs hover, and relax your shoulders down away from your ears without letting your arms drop to the ground. 3. Press your low back gently toward the floor and brace your midsection before the first rep, as if preparing for a light punch to the stomach. 4. Exhale as you simultaneously curl your shoulder blades off the floor and bend your knees, drawing them in toward your chest. 5. Sweep your extended arms forward so your hands pass alongside your knees or shins at the top of the crunch. 6. Pause for a beat in the tucked position with your torso folded toward your thighs and your abs fully squeezed. 7. Inhale as you reverse the path under control: straighten your legs back out to the hover while your arms travel back overhead and your torso lowers until your shoulder blades approach the floor. 8. Do not let your head or shoulders rest fully down between reps; keep light tension in the abs through the open position. 9. Reset your brace briefly, then begin the next tuck. Breathe out on every knee-in, in on every extend. 10. Finish the set by lowering your heels to the floor and relaxing your arms down at your sides. ## Tips & Tricks - If your heels drift toward the floor as you fatigue, that is the first sign the set is ending; bend your knees slightly or stop rather than losing the leg hover. - Watch for the low back arching and peeling off the floor as the legs extend out; shorten the leg extension by keeping the knees a little bent until you can hold the hollow position cleanly. - Do not lead the curl with your chin. Keep roughly a fist's width of space between chin and chest, and let the shoulder blades do the lifting, not the head. - The arms are a counterweight, not a swing. If you find yourself flicking them forward to generate momentum, slow the tempo and pause for one second at the top of each tuck. - Pair the exhale with the knee tuck. Exhaling hard as you fold helps the ribs drop and the abs shorten, which is exactly what the Knee In And Out Crunch is asking for. - Keep both knees bending evenly; one knee collapsing inward or one arm reaching further than the other usually means the obliques are being bypassed and the hips are rotating. - Place a folded towel or thin pad under your tailbone if the floor feels sharp when your hips roll slightly during the tuck. - Anchor the movement to a tempo, such as one second in and two seconds out, so the return phase actually builds tension instead of falling back to the start. - If the full version is too demanding, regress by keeping your heels on the floor and only moving torso and knees, or by tucking one leg at a time. ## Frequently Asked Questions ### Which muscles does the Knee In And Out Crunch work? The rectus abdominis is the primary mover, with the lower fibers doing much of the work as the knees draw in. The hip flexors assist each tuck and the obliques stabilize your torso so the fold stays straight. ### Why do my hip flexors feel the Knee In And Out Crunch more than my abs? That usually means your torso is staying down while only the legs move. Focus on curling the shoulder blades off the floor every rep so the abdominals share the work, and exhale hard as the knees come in. ### Is the Knee In And Out Crunch suitable for beginners? It can be, but it is easier to learn after mastering a basic crunch and a hollow-body hold. Beginners can regress it by keeping the heels on the floor or tucking one leg at a time until the coordination feels natural. ### How high should my legs be in the starting position? Your heels should hover just a few inches above the floor with your legs straight, low back flat against the ground. If your back arches or strains at that height, raise the legs slightly or add a gentle knee bend. ### Should my hands touch my knees at the top of the Knee In And Out Crunch? They can sweep alongside your knees or shins, but touching them is not the goal. Reaching forward is simply a cue that helps the ribcage curl toward the pelvis; do not stretch or grab at the knees. ### How many reps should I do? Work in sets of 10 to 15 controlled reps, or time sets of 20 to 30 seconds. Stop when your shoulder blades no longer lift cleanly off the floor, since sloppy reps mostly load the hip flexors and neck. ### What can I substitute if the Knee In And Out Crunch is too hard? A reverse crunch with bent knees trains a similar lower-abdominal pattern with less demand on coordination. Once that feels solid, add the arms reaching overhead and progress toward the full version. ### Can the Knee In And Out Crunch hurt my lower back? It can feel uncomfortable if your legs extend too low for your current control, letting the low back arch under load. Keep the heels higher, shorten the leg extension, and stop if you feel pressure in the lumbar area rather than muscular effort in the abs. ### Do I need any equipment for this exercise? No, it is a body weight movement. An exercise mat is recommended to cushion your spine and tailbone on hard floors, but nothing else is required.