Day 49 gives the jumping jack a floor-based twin. Four 15-second intervals - jumping jacks, plank jacks, jumping jacks, plank jacks - three to seven sets, one minute of rest.
A plank jack is exactly what it sounds like: from a high plank, both feet jump wide and back together while everything above the waist stays completely still. It is the same leg pattern as a jumping jack rotated ninety degrees, and it turns out to be far harder in this orientation, because your core has to stop your hips from bouncing every time your feet land. Alternating the standing and floor versions inside one set is the cleanest illustration of what the back half of this program has been doing - taking a familiar cardio movement and making you hold a plank while you do it.
Keep your hips low and steady on the plank jacks and let the feet do all the travelling - if your backside is rising with each jump, slow the tempo. Land on the balls of your feet. On the standing jacks, arms all the way overhead and a light landing through the whole foot.
The same jack, two orientations - and gravity is a very different opponent from down there.
Make it Harder: Take the plank jacks on your forearms rather than your hands and keep the same tempo.
Make it Easier: Step the feet out and in one at a time on the plank jacks instead of jumping them.
