You touched on it..:: the study was drug free. AAS changes all of this. I have read tons of studies on LISS, HIIT, and fasted cardio unfortunately there is little on the effect of AAS and these conditions.
I've always burned the most fat first thing in the morning before breakfast and it showed on my body fat scale, with or without dnp and phentermine. Problem is once you stop this routine it creeps right back on and getting up an hour early to do cardiovascular gets old fast.
Iam 47 yrs old and have 20plus years of stage time. Fasted morning cardio was really my only way to lose that hard to reach fat storages. Yes I did lose “ some” muscle but as a competitive bodybuilder what I lost was min. Compared to conditioning needed.