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 nine aerobic training (AT; 90 min at 70% V˙O2max) and nine high-intensity interval training sessions (HIT; 8 × 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, first performing AT and then, 1 h later, performing HIT. Pretraining and posttraining measures were a resting muscle biopsy, metabolic measures during steady-state cycling, and a time trial.
Results: Power output during HIT was 297 ± 8 W in LOW compared with 323 ± 9 W in HIGH (P < 0.05); however, time trial performance improved by ∼10% in both groups (P < 0.05). Fat oxidation during steady-state cycling increased after training in LOW (from 26 ± 2 to 34 ± 2 μmol·kg−1·min−1, P < 0.01). Plasma free fatty acid 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 μmol·kg−1·min−1, P < 0.05). Training with low muscle glycogen also increased β-hydroxyacyl-CoA-dehydrogenase protein content (P < 0.01).
Conclusions: Training with low muscle glycogen reduced training intensity and, in 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 the enhanced metabolic adaptations in skeletal muscle.
1School of Sport and Exercise Sciences, University of Birmingham, Birmingham, UNITED KINGDOM; 2Functional Food Centre, School of Life Sciences, Oxford Brookes University, Oxford, UNITED KINGDOM; 3Department of Fetal Medicine, Division of Reproduction and Child Health, Birmingham Women's Hospital, Birmingham, UNITED KINGDOM; and 4Functional Molecular Biology Laboratory, Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee, UNITED KINGDOM
Address for correspondence: Asker E. Jeukendrup, Ph.D., School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; E-mail: email@example.com.
Submitted for publication October 2009.
Accepted for publication February 2010.
C.J. Hulston's current address: Copenhagen Muscle Research Centre, Rigshospitalet, Section 7652, Copenhagen, Denmark.
A. Philp and K. Baar's current address: Functional Molecular Biology laboratory, University of California, Davis, CA.