Training in a state of glycogen depletion limited performance but increased fat burning. It would be interesting to see this compared with Phinney's work on low carb and endurance training.
Training with Low Muscle Glycogen Enhances Fat Metabolism in Well-Trained Cyclists.
PURPOSE:: To determine the effects of training with low muscle glycogen on exercise performance, substrate metabolism, and skeletal muscle adaptation. METHODS:: Fourteen well-trained cyclists were pair-matched and randomly assigned to HIGH or LOW-glycogen training groups. Subjects performed 9 aerobic training (AT; 90 min at 70% VO2max) and 9 high-intensity interval-training sessions (HIT; 8 x 5 min efforts, 1 min recovery) during a 3-wk period. HIGH trained once daily, alternating between AT on day 1 and HIT the following day, whereas LOW trained twice every second day, firstly performing AT and then 1 h later performing HIT. Pre and post-training measures were a resting muscle biopsy, metabolic measures during steady state cycling (SS), and a time trial (TT). RESULTS:: Power output during HIT was 297 +/- 8 W in LOW compared with 323 +/- 9 W in HIGH (P<0.05), however, TT performance improved by ~10% in both groups (P<0.05). Fat oxidation during SS increased after training in LOW (from 26+/-2 to 34+/-2 mumol/kg/min, P<0.01). Plasma FFA oxidation was similar before and after training in both groups but muscle-derived triacylglycerol oxidation increased after training in LOW (from 16+/-1 to 23+/-1 mumol/kg/min, P<0.05). Training with low muscle glycogen also increased beta-hydroxyacyl-CoA-dehydrogenase protein content (P<0.01).
CONCLUSION:: Training with low muscle glycogen reduced training intensity and, in terms of performance, was no more effective than training with high muscle glycogen. However, fat oxidation was increased after training with low muscle glycogen, which may have been due to enhanced metabolic adaptations in skeletal muscle.