Glycogen is obtained from carbohydrate and glycogen stores are energy stores in both the muscle and liver. Liver can store about 50 g of glycogen and muscles about 400-450 g. These figures are for a "normal" 180 lbs guy, so results will vary according to the amount of muscle mass. When these stores are full, the excess carb is converted to fat (de novo lipogenesis). HIIT can be quite glycogen depleting. A lifting session usually end ups lowering the glycogen stores by 25% and a single 30 sec sprint can lower the levels by 30%!! (linky : http://jap.physiology.org/cgi/content/full/87/4/1326) So if the partionning effects are caused by an exercice induced change (both a higher glucose uptake and then a higher insulin sensitivity) it should be fine. (reading : http://www.ncbi.nlm.nih.gov/sites/en...rch=1 6036907 ) Depletion of glycogen stores to a certain extent will prevent de novo lipogenesis. HIIT is also pretty glycogen depleting, 10 bouts of 1 min decreased muscle glycogen by almost 60% and most of this depletion occurs during the first couple of bouts : When at low levels, glycogen stores in muscle can store more glycogen than it usually could (it's called carbohydrate loading or glycogen supercompensation) but this effect can't be repeated two days in a row. That would mean that depleting glycogen stores during 2-3 days, followed by a high carb day (2g per pound of carb and 1g/lb of protein, fat kept at about 30-50 g). So by controlling carb intake and exercise being done during this day, most people could get a nice intake of carb while preventing some fat gain.