Effect of Glycogen Stores and Liquid Food Intake on Fat and Carbohydrate Utilization During Exercise

Abstract

Aim: It is well known that fasting activates fat metabolism. Besides, in recent years many research studies accumulated that commencing exercise with low muscle glycogen is an effective strategy to activate fat metabolism and gain more training adaptation than normal muscle glycogen state. To test whether exercise with low glycogen stores is superior to activate fat metabolism we set up this study.

Subjects and Methods: Nine male triathletes participated in this study. Consumption of liquid food breakfast or fasted (overnight) exercise trials were done separated by one week intervals with crossover, counterbalanced randomized design. Prior to the study all the subjects attended to maximal exercise test to determine VO2 peak and peak power output (PPO). For both trial subjects attended to two 60 min exercise sessions at 70% VO2 peak (Liquid food Exercise: LE1, LE2 or Fasted Exercise: FE1, FE2) with one hour resting period, thus the second exercise period aimed to be performed with low muscle glycogen stores.

Results: Total fat oxidation in LE1 was significantly higher than both LE2 (LE1-LE2; 13.4±6.7 g/60 min versus 23.9±7.6 g/60 min, p<0.001) and FE2 (LE1-FE2; 13.4±6.7 g/60 min versus 27.4±6.0 g/60 min, p=0.002).

Conclusion: In conclusion we found that there is no superior effect of overnight fasted state exercise with depleted muscle glycogen stores over liquid food given counterpart to increase fat metabolism. Furthermore, it seems that, the major determinant improving fat metabolism in this study is the state of muscle glycogen stores rather than the level of liver glycogen stores.