Creatine supplementation spares muscle glycogen during high intensity intermittent exercise in rats

First, the animals were submitted to a high intensity intermittent maximal swimming exercise protocol to ensure that CR-supplementation was able to delay fatigue (experiment 1). Then, the CR-mediated glycogen sparing effect was examined using a high intensity intermittent sub-maximal exercise test (fixed number of bouts; six bouts of 30-second duration interspersed by two-minute rest interval) (experiment 2). For both experiments, male Wistar rats were given either CR supplementation or placebo (Pl) for 5 days.As expected, CR-supplemented animals were able to exercise for a significant higher number of bouts than Pl. Experiment 2 revealed a higher gastrocnemius glycogen content for the CR vs. the Pl group (33.59%). Additionally, CR animals presented lower blood lactate concentrations throughout the intermittent exercise bouts compared to Pl. No difference was found between groups in soleus glycogen content.The major finding of this study is that CR supplementation was able to spare muscle glycogen during a high intensity intermittent exercise in rats.Creatine (CR) plays an important role in rapid energy provision during muscle contraction involving the transfer of the N-phosphoryl group from phosphorylcreatine (PCR) to ADP to regenerate ATP through a reversible reaction catalyzed by phosphorylcreatine kinase (CK). Moreover, Cr is responsible for energy transfer from mitochondria to cytosol. This function is only possible due to the presence of different PCK isoforms linking the sites of ATP generation (i.e., mitochondria; Mt-PCK) to those of ATP consumption (i.e., skeletal muscle and brain; MM-PCK and BB-PCK, respectively) [1,2].Several studies have focused on the ergogenic capacity of CR loading since its efficacy to increase skeletal muscle CR content in humans has been demonstrated [3]. In fact, a growing body of evidence points out the benefits of CR supplementation in short-term high intensity activities (for review, see [4]), although the mechanisms by which t