Drew C. answered 08/21/19
Personal Trainer & Kickboxing Instructor with 15+ Years Experience
The key takeaway here is that you don't want to do HIIT or other high-intensity cardio two or more days in a row. HIIT is a great way to burn calories, increase cardiovascular efficiency, and not spend a ton of time in the gym, but it's pretty hard on your body. What you're reading is cautioning you against overtraining.
You don't HAVE to do low-intensity cardio the day after a HIIT session, but if you do choose to do some cardio, make sure it's lower-impact and focused on giving your body ample time to recover.