Day 16 is holds and nothing else. Six positions, 2 minutes each, in the order on the card: a squat hold, a raised arms hold, a calf raise hold, an elbow plank hold, a side elbow plank hold and a superman stretch hold. Twelve minutes of work in total, and the card's one instruction is to split each hold into manageable sets if and when necessary - 2 minutes can be four pieces of 30 seconds with a short rest between, as long as the pieces add up. The raised arms hold is standing with both arms straight out in front at shoulder height. The calf raise hold is up on the balls of the feet with the hands behind the back. The superman stretch hold is face down with the arms reaching forward and the legs lifted off the floor. The side plank time is split, one minute per side.

Endurance here means the literal thing: how long a muscle can keep doing its job without a break. The three standing holds cover the legs from the quads in the squat down to the calves on the raise, with the shoulders taking the raised arms hold in between. The three floor holds cover the trunk from three directions - front in the elbow plank, side in the side plank, back in the superman. Where Day 11 gave the plank a level and a time, today everyone holds the same 2 minutes and the levels are replaced by the permission to split. That permission is the program's way of setting the target above where you are and letting you get there in pieces.

Squat hold: thighs near parallel, weight in the heels, arms out front as drawn. Raised arms hold: arms straight, shoulders down, hands at shoulder height - they will want to sink, and the hold is keeping them up. Calf raise hold: as high onto the toes as you can and steady. Elbow plank and side plank keep their standards from Day 11. In the superman, lift the arms, chest and legs together, keep the neck long and breathe; a small lift held for two minutes beats a big lift held for ten seconds.

Twelve minutes of not moving is the hardest kind of moving - Day 16 measures endurance by stillness.

Make it Harder: Do each 2-minute hold unbroken, and keep the arms out in front for the entire squat hold.

Make it Easier: Break every hold into 30-second pieces with a short rest between them, and take the plank holds from the knees.