Since it's been raining nearly every day lately where I live, I've been having to do my cardio indoors. What I do is sprint up the stairs 50 times (broken up into 5 sets of 10, 2 minute rest in between sets). It takes me about 15-20 minutes to finish this and I do it 4 days a week, the other 3 are lifting days. My question is, is this a good replacement for normal outside HIIT cardio?