Friday, November 12, 2010

Glycogen-Depletion Has no Effect on Selected Marker of Skeletal Muscle Adaptation

In a recently published study, Camera et al. (Camera. 2010) investigated the effect of isolated glycogen depletion on the rpS6 phosphorylation, a process which is closely related to the insulin/insulin-like growth factor (IGF) signalling pathway that is generally believed to be part of the positive adaptation processes of resistance exercise.

By having their subjects perform a unilateral cycling exercise the evening before the test session, the scientists established a "divergent muscle glycogen content that was  higher in the control leg (Norm) than in the Low leg at rest (383 ± 43 vs. 184 ± 14 mmol/kg dry wt; p < 0.05)". Thus, with the "normal" leg, they had an intra-(not inter-)individual reference for the results of the muscle biopsy after the testing protocol. Other than one might suspect, there was yet no difference between the rpS6 phosphorylation in the glycogen-depleted vs. the normal leg, which lead the scientists to conclude:
These results indicate that low muscle glycogen levels fail to suppress phosphorylation of a key component in skeletal muscle translation initiation following high-intensity resistance exercise when protein/carbohydrate supplementation is provided during recovery.
If we assume that the psS6 phosphorylation is in fact an adequate measure of the anabolic response to exercise training, we may further assume that the practice of "training" does not preclude positive adaptations, if proper amounts of nutrients (in the study these were (20 g whey protein + 40
g maltodextrin) are absorbed in the course of the recovery period.