What is the most difficult workout for you?

I have been doing Fitness Blender's 4/5 workouts, and I was barely sore the next day. That calls for huge improvement, right?

I used to get sore from 3/5 workouts, but now I feel that they are not as hard as I imagined. I do 4/5 HIIT workouts 3 times a week, along with cardio and strength training.

I did a brutal 2 HIIT workouts yesterday, and was surprised that I wasn't sore. Can any of you suggest harder 4/5 or 5/5 workouts that a 13 year old can do?

I really would like to hear from the FB family!