Level 6 Valued Member
Joel Jamieson has done some very interesting studies and real-life training by going against the 'HIIT' theory. His website is where I first started understanding the negative side of HIIT training.
All Pain, No Gain: Why the High-Intensity Training Obsession Has Failed Us All
Jamieson fully incorporates high intensity training in his programs (Ultimate MMA Conditioning), he's against the use of HIIT exclusively, while excluding aerobic training.