Many perform steady-state running.
Many think they are doing it for weight loss.
The research shows that incorporating all three tactics (diet/aerobic exercise/weight resistance training) will help one to lose more fat than diet alone, aerobic exercise alone or even a combination of the two.
This is an easy way to start HIIT; choose your cardio method and begin by performing 15 seconds of a sprint and rest for 30 seconds.
Repeat 10 times or until you feel "done" - in other words, don't get sick performing this routine.
After three to five sessions of this, it should begin to get easier.
When 15 seconds feels alright - bump it up as you want gradually.
Be committed to perform the intervals two times per week with a day of rest between. Add in one 20-minute session of moderate cardio activity.
Most get successful with these but the older ones may need special exercise and diet tip or even blood test before getting started for your fast and safety.