Day 13 pairs three standing exercises with three floor ones and alternates them all the way down: 20 high knees, 4 climbers, 20 jumping jacks, 4 plank jacks, 20 butt kicks and 4 alternating arm and leg raises. That is one set - rest 2 minutes and go again, for 3, 5 or 7 sets.
The rhythm here is deliberately uneven. Every standing block runs 20 reps at speed; every floor block runs 4 reps and demands control. Climbers fire the knees in toward the chest in a plank position. Plank jacks keep the upper body still and jump the feet wide and back in, which loads the shoulders while the hips work. The alternating arm and leg raises are the slowest thing in the session: still in a plank, you lift one arm and the opposite leg at the same time and hold the body level, which is a balance problem more than a cardio one. Going to the floor for four careful reps in the middle of a fast session is a genuine test of whether you can switch gears.
High knees and butt kicks are both run in place, one bringing the thigh up and the other bringing the heel to the glute, and both want a quick cadence rather than big movements. In climbers and plank jacks, the shoulders stay stacked over the wrists and the hips stay low. For the arm and leg raise, lift only to the height where your back stays flat, hold for a beat, and swap sides without letting the hips tip.
Six exercises, two speeds, and the switch between them is the whole point of the day.
Make it Harder: Hold each arm and leg raise for a 3-count at the top before changing sides.
Make it Easier: Walk the plank jacks wide and back in instead of jumping, and keep the standing blocks fast.
