Band on the ankles, legs alternating, lower abs and quads loaded.
Press your lower back into the floor. Don't let it arch as your legs move.
Raising one straight leg against a band anchored by the other makes the quads work double duty, holding the knee locked while the hip flexors lift the leg against growing tension. The grounded leg is not passive, the glutes press it down to keep the band's anchor from drifting up. It is a floor move that turns a basic leg raise into loaded, one-leg-at-a-time work with nothing but a mini band.
Your trunk is losing the fight against the lever of your leg. Press your lower back into the floor before each rep, and shorten the range or slow down until you can keep it there.
Different, not easier. One leg means a shorter total lever on your spine, but the band adds resistance to the lift and the down leg has to actively pin the anchor, so both sides work every rep.
Around both ankles with your feet about hip-width apart so there is tension before the rep even starts. If the band goes slack at any point, start with your feet slightly wider.
