The benefits of HIIT workouts are amazing. HIIT workouts however are also hard. Extreme HIIT is a difficulty level V workout that will push your cardiovascular fitness and aerobic capacity to the limit and test your recovery time. This isn't suitable for beginners or those coming back to fitness after a long layoff but have it on your horizon anyway. And for this particular workout EC is a must.
Extra Credit: 1 minute rest between sets.