Carbohydrate Availability and Training Adaptation: Effects on Cell Metabolism

John A. Hawley; Louise M. Burke

Disclosures

Exerc Sport Sci Rev. 2010;38(4):152-160. 

In This Article

Interaction of Muscle Glycogen and Glucose Availability and Training Adaptation

To date, the only investigation to systematically determine the interactive effects of low muscle glycogen content combined with altered exogenous carbohydrate availability on training adaptation and performance was performed by Morton and colleagues.[24] They studied three groups of recreationally active males who completed 6 wk of high-intensity, intermittent run training (a total of 24 training sessions each consisting of 15 min of running at a speed corresponding to ~90% of V·O2peak, 15 min of running at 25%-50% of V·O2peak, and 20 min of running at ~70% of V·O2peak). In this study, two groups trained twice a day, two sessions per wk (one session in the morning, the other in the afternoon), whereas the third group trained once per day, 4 d/wk. This design ensured each subject completed the same amount of training, but that subjects in groups 1 and 2 performed the second exercise session with a 35% to 45% reduced glycogen level. To allow for the determination of the effects of exogenous glucose supplementation, subjects in group 1 consumed a 6.4% glucose solution (GLU) immediately before and throughout every second training session (LOW+GLU), whereas subjects in group 2 consumed an identical volume of placebo (PLA) (LOW+PLA). A control group commenced each training session with normal glycogen stores and did not consume any beverages throughout the sessions. Muscle biopsies from the vastus lateralis and gastrocnemius were taken before and after the training intervention.

In contrast to the findings of Hansen et al.,[15] performance (determined as intermittent run time to exhaustion) was similar in all three groups (22%-24% increase; P < 0.001). The training-induced increase in V·O2peak also was similar between groups (8%-10%; P < 0.001). Several training-related proteins, including COX-IV and the peroxisome proliferator-activated receptor γ coactivator (PGC-1), were significantly increased after training (P < 0.05), but there were no differences in the magnitude of change between groups. In contrast, the training-induced increase in the maximal activity of SDH was greater in LOW+PLA than the other conditions (P < 0.05). Morton and coworkers[24] concluded that "training under conditions of reduced carbohydrate availability from both endogenous and exogenous sources provides an enhanced stimulus for inducing oxidative enzyme adaptations of skeletal muscle, although this does not translate to improved performance during high-intensity exercise."

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