Day 2 is a cardio circuit built from two moves that trade places. Read the list top to bottom: 10 high knees, 4 climbers, 10 high knees, 4 climbers, and so on for five rounds of each. That whole list is one set. Rest up to 2 minutes, then repeat for 3, 5 or 7 sets depending on your level. There is no pause between the high knees and the climbers; the point is to keep moving from standing to the floor and back without letting the pace fall.
High knees are the engine here: a running motion on the spot with each knee driven up to hip height, 10 reps meaning 5 per leg. Climbers put you in a plank and pull one knee toward the chest at a time, 4 reps being 2 per leg. The constant change of level, up on your feet and then down on your hands, is what makes a short list feel like a long run. By the third round the transitions are doing as much work as the exercises.
On high knees, stay light on the balls of your feet and pump the arms as if you were sprinting; height beats speed at first. In the climbers, keep the hands under the shoulders and the hips level with the back, and bring the knee in far enough that the thigh comes close to the chest. Get up and down cleanly rather than collapsing into the plank.
Two exercises, one rule: never let the floor slow you down.
Make it Harder: Double the climbers to 8 per round and keep the high knees at 10.
Make it Easier: Turn the high knees into march steps at the same count and take the climbers slowly.
