Day 19 is the only short day built on the 30 and 10 pattern rather than flat 20-second stations. Thirty seconds in an elbow plank, 10 seconds of elbow plank crunches, three times through, then a minute of jumping jacks. Three sets and nine minutes, of which two full minutes per set are spent on your elbows.
The pairing is a hold and its interruption. The elbow plank asks your whole trunk to stay rigid; the crunches then break that rigidity on purpose by drawing one knee in toward your chest and back out, alternating sides, while everything else stays exactly where it was. Ten seconds is short, but coming out of a static hold into movement and straight back into stillness is harder than either would be alone, because the muscles never get to settle into one job. Ninety seconds of plank per set is a real number, and the minute of jumping jacks that follows exists to remind you this is still a conditioning program.
Set your elbows directly under your shoulders with your forearms parallel, squeeze your glutes, and hold your hips at the height of a straight line between your shoulders and heels. In the crunches, bring the knee toward the same-side elbow without letting your hips lift or your back round, and place the foot back down under control. Breathe through the holds rather than bracing against them. If your lower back starts to complain, that is your hips sinking rather than your abs failing, so lift them and carry on.
Two minutes of elbows and one minute of jumping - the shortest working day here still asks for all of it.
Make it Harder: Extend the crunching leg straight back to full length before bringing the knee in again.
Make it Easier: Break each 30-second hold into two halves with a brief reset on your knees in between.
