Are there high intensity routines that i can do in my living room and then alternate that with my walking routine? (coachcalorie.com)
If you are new to HIIT, you should aim for performing high intensity routines for about 30 - 60 seconds, followed by a break of two minutes (depending on the type of the workout). (fitnessandpower.com)
Now I will say that if someone is really deconditioned and can't handle higher intensity exercise routines just yet, this still doesn't mean that they can't simply use lower intensity routines, but still use it in a «variable intensity» fashion, by alternating between higher and lower exertion levels throughout the workout. (truthaboutabs.com)