Are you looking for a way to really chisel your upper abs? Cable crunches are a great upgrade, but only if you do them correctly!
Doing crunches on a cable apparatus offers one huge advantage over doing them on the floor: The cable allows you to increase resistance, enabling you to train to failure using heavier weights and fewer reps. This increased emphasis on strength and hypertrophy is exactly the kind of workout the fast-twitch muscle fibers in your abs need to get big and carved.
Other than the extra resistance, this version of the crunch is virtually the same as the one you do on the floor, with one exception: If you screw up how you do the crunches, you can completely wipe out all of the great benefits you get from using a cable.
Not Rounding Your Back
Keeping your back in a neutral or slightly arched position is good form when you’re training with heavy loads. After all, rounding your back when you’re doing squats, deadlifts, or bent-over rows can damage your spine.
But the problem with maintaining an arched back on ab day is that it prevents you from actively contracting your rectus abdominis (RA) muscles through a full range of motion. If you can’t contract your main ab muscles, you’re not getting any closer to that rippling six-pack.
For abs, you need to round your back to unlock the arch in your lumbar spine, which enables you to shorten the RA muscle fibers—especially those in the upper RA region. The lower back muscles (erectors) are antagonists to the rectus abdominis: when one is contracting, the other is being stretched. If the erectors can’t stretch, the abs can’t contract. And if they can’t contract, they can’t grow. It’s as simple as that!