Double post dog ****!
I struggled on the treadmill without much food in the body....duh. But got through it. Was a big fat pale of sweaty mess. Good thing I work out in the minor league rec center gym where a guy on the treadmill next to me had an oxygen mask.
What I found on lower carb diets was that the first ten minutes of any aerobic workout felt awful. Eventually, my body would switch to burning fat and I could actually do longer (somewhat lower intensity) workouts. But it was hell if I was trying high intensity interval training or something).
Also, other's mileage may vary, but my muscular endurance went to hell after Atkins and it's never really come back. What I mean is that one set of bench, at just about any weight, just burns me out. My theory is that it dropped my testosterone levels (others have reported similar results anecdotally), but I just don't know. I just know that the two longest periods of ketogenic diets I've ever been on resulted in some pretty serious loss of strength and big spurts of hair loss.