Straight legs, controlled lift, lower abs on fire.
Keep your lower back flat. If it arches, don't lower your legs as far.
Raising straight legs from a hover to vertical puts a long lever on your abs, which have to fight to keep your pelvis tucked and your lower back pinned through every degree of the arc. The slow lowering back to just above the floor is where most of the value lives, and where most people leak form. It is a bodyweight core staple because the progression is built in, just lower slower and hover longer.
Shorten the range. Only lower your legs as far as your back stays flat, even if that is halfway. Hands under the glutes help, and as your abs strengthen the range earns itself back. An arched back means the hip flexors have taken over.
They are a regression, not a cheat. Bending the knees shortens the lever so you can own the pelvic tilt first. Straighten the legs gradually over weeks, a strict bent-knee raise beats a flailing straight-leg one every time.
Lying raises let you check your lower back position against the floor, which makes them the better teacher. Hanging raises add grip, lat, and stability demands with a bigger range. Master the floor version first, then take it to the bar.
