Feet in the straps, plank goes brutal.
The straps want to swing your feet, lock your core to kill the wobble.
Putting your feet in the cradles removes the floor's stability from your plank, and your core spends the whole timed hold cancelling the sway of two free-hanging straps. Nothing about the shape changes, it is the same straight line from head to heel, but the base beneath your feet never stops testing it. It earns its place as the standard plank progression on straps, the position everything else here builds from, and the fastest way to find out whether your brace is real.
Your feet can swing. The floor holds you still for free, the straps make your core pay for every second of stillness, which is why hold times drop sharply when people first try it.
The steps allow both. Forearms are the standard starting point, moving up to straight arms raises your body angle slightly and adds a shoulder stability demand.
Long enough that the line never breaks. Build from twenty to thirty second holds with zero strap swing, and treat a wobbling sixty seconds as worth less than a silent thirty.
