A lot of easy cardio at 55-75% is healthy. 5-10 minutes of sprinting at 95-100% is healthy.

However, how much and of what intensity should a workout be? As far as I've read, these workouts are somewhat intense and last 10-45 minutes.

But, isn't that too (or not enough) intense and too long? Isn't that some form of high intensity dangerous cardio?