Day 13 mixes the two cardio days you have done. Three exercises, 20 seconds each: step jacks, march jacks, step Ts - the first two from Day 1, the third from Day 5, one minute per set with a minute of rest, sets by level. Nothing new to learn; today is about pace and staying continuous.
Step jacks: step out, arms overhead, back and alternate. March jacks: knee up as the arms sweep overhead, alternating legs. Step Ts: step out to the side and open the arms into a level T, close and go the other way. Reach up, knee up, arms out - two exercises that send the arms overhead and one that sends them sideways, all sharing the same low-impact footwork.
With no new exercise to think about, spend the attention on quality: full reach on the jacks, knee to hip height on the marches, arms exactly level on the Ts. Keep the transitions instant - the moment the timer beeps, you are already in the next move. If you have been doing Level I, today is a good day to try one extra set and see how it feels.
No new moves, so the only thing left to improve is how well you do the old ones.
Make it Harder: Land on the ball of the foot on every step and lift the heel as the arms rise - the calves join the cardio.
Make it Easier: Slow the march jacks to a march with the arms rising only to shoulder height.
