Here is a simple program to introduce high-intensity interval training (HIIT) into your cardiorespiratory exercising. Please know, however, that HIIT is not advised for beginning exercisers and should not be used more than twice per week—steady-state cardio should be used on other days. PLEASE CONSULT YOUR DOCTOR BEFORE BEGINNING ANY NEW EXERCISE PROGRAMS.

https://www.acefitness.org/education-and-resources/lifestyle/blog/3768/try-this-hiit-workout-on-the-elliptical-trainer