Here is some interesting reading:
Keep in mind the author is was not intending a LC audience. When he speaks of 'hitting the wall' it is glycogen depletion and this (to us) is our gateway into ketosis.
Portions copied from the addresses shown.
http://www.volleyweb.com/docs/metabolism.html
Within the first 20 minutes or so of moderate exercise, a person uses up
about one-fifth of the available glycogen. As the muscle devour their own
glycogen, they become ravenous for more glucose and increase their uptake
of blood glucose 20-fold or more. Very soon the blood glucose start to fall
and the hormone glucagon is released into the blood. This hormone acts on
the liver to promote the breakdown of glycogen to glucose, the conversion
of amino acids to glucose and the release of glucose to the blood, to keep
the blood glucose level constant. The protein syntheses is decreased and the
use of protein as energy is increased.
The fat stores are virtually unlimited source of energy but without glucose
( from glycogen ) the exercise performance is greatly impaired. If the
glycogen stores are depleted, glucose have to come from the outside,
(usually through carbohydrate drinks). As glycogen stores are depleted
hypoglycemia hits. It brings nervous system function almost to a halt,
making exercise difficult, if not impossible. This is "hitting the wall" in
a marathon, and different from the sudden fatigue that one feels after a set
of weightlifting. (P. Astrand, Something old, and something new... very new, Nutrition
Today, June 1968 pp. 9-11.). Weightlifters use relative more glucose vs. fat
than runners do, but the calories burned per hour are much lower. The
possibility for a trained weightlifter to "hit the wall" during long and
intense session, are almost zero.
After the exercise(.......) The
metabolism is up to 25% higher than normal.
Ok... More interesting reading from:
http://www.wannabebigforums.com/showthread.php?t=49035
"The abstract mentions that, "Whole-body CHO oxidation increased sixfold and fat oxidation decreased > 90% on surplus CHO diets." When carb loading, the body increases carbohydrate oxidation and decreases fat oxidation. The fat that you consume is stored, while fat burning slows down. In this way, fat balance may increases during a positive calorie balance even though carbs are not being converted to fat. This is one of the reasons for keeping fat intake low while refeeding. If fat intake is low while carb intake is a high and calorie balance is high, then the carbs will refill glycogen reserves and fat balance will not increase as much as would be predicted by calorie balance during the transient refeed.
Similarly, if you burn carbs during cardio, glycogen stores decrease. This causes fat oxidation to increase and CHO oxidation to decrease during the period while glycogen stores remain low. In this way burning carbs during cardio can cause you to lose as much body fat as burning fat during cardio. If anything the higher intensity carb-burning cardio would have a small advantage due to things like nutrient partitioning and AMPK activation."
(((This is a different opinion that the first author!!)
So my thoughts are that... An intense workout that burns enough glycogen can stimulate ketosis after a carbup. Especially if ones body is well adapted (by prolonged past ketosis) to enter this state.
Low intensity cardio can also work because as muscle glycogen gets lower one's body will draw on liver glycogen to maintain blood sugar level. Sustained for enough time... liver glycogen will be depleted.
My thoughts right now include... Why not put the glycogen to good use and build some muscle while you're depleting it...?