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