In case you haven’t heard, crunches and sit-ups are overrated. The best way to build the six-pack of your dreams is almost never to do rep after laborious sit-up rep.
That’s why the Pallof press remains one of the best hidden-gem ab exercises. To do the Pallof press, wrap a resistance band around machine or another fixed surface at about chest height so the band is parallel to the ground. Then grab the band or the grip of a cable machine in both hands and hold it at shoulder height with both arms in the center of your chest. Brace your core and extend your arms forward. Hold for at least 2 seconds (or longer, which is even better.) Aim for 3 sets of 8 to 10 reps.The resistance of the band or cable will try to pull your torso back towards it. Your core muscles will have to brace to fight that pull and keep your torso centered, and any weak muscles (say, your lower back, or perhaps an imbalance in oblique strength) will have to work overtime to keep you in stable position. This is also a great way to help improve the symmetry of your abs.
The key with the Pallof is to spend plenty of time with your arms extended. When you draw your arms close to your body, you’re taking tension off your core and “resting,” so work to keep those momentary breathers at a minimum. And when you extend, do so deliberately, establish a strong, sturdy position, and hold steady for a few seconds.
The standing Pallof is the easiest version, so once you master that, step things up. Tall kneeling Pallofs will challenge you more, forcing you to fire more aggressively with your glutes. Once you can do 3 sets of 8 to 10 reps with those, progress to half-kneeling Pallofs, kneeling on the knee closest to your cable. Make sure to externally rotate your outer hip, and keep working to stay steady.
Whatever you do aim for 3 sets of 8 to 10 reps. You can build them into your routine every day. Your core should be tight all the time, and no move will tighten it up quite like this one.
Source: How to Get a Six-Pack Without Doing a Single Sit-Up