See this link, bottom of page:
"Very Low Carbohydrate Diet and Preservation of Muscle Mass"
"The perception that the VLCARB leads to progressive loss
of muscle protein apparently comes from the poorly controlled
"Turkey Study" published in the New England Journal
of Medicine in 1980 . The authors of this study
reported that the protein-only diet subjects were losing
nitrogen yet gaining potassium. As pointed out by Phinney
[13,14], however, potassium and nitrogen losses are
closely related, as they are both contained in lean tissue.
This anomaly occurred because the authors assumed the
potassium intake of their subjects was based upon handbook
values for raw turkey, but half of this potassium was
being discarded in the unconsumed broth. Deprived of
potassium, these subjects were unable to benefit from dietary
protein and thus lost muscle mass ."
If anything, those who've been on a calorie restricted high carb diet for a while will regain the lost lean tissue once they go on a VLCARB/VHFAT ad libitum diet.
About the sprint and HIIT/Tabata. I think that 45 seconds for 200 meters is not all out. All out for a top athlete is <10s/100m. For 200m it's <20 seconds. But I agree here that the intensity is relative. It's relative to our current potential. But that will improve over time and from one workout to the next. Below is the Tabata protocol as an example.
20s sprint 170% Vo2Max
10s full rest
repeat 8 times
Any exercise can be used as long as the entire body is used for it. Running, cycling, jumping jacks, burpees, and a few barbell lifts such as the clean or power clean can be used.
That's my take on it.