The Effects of Creatine Supplementation on Muscular Strength and Endurance in Mice

David Howden, Craig Boekenoogen, Jared Wagoner, Shaina Miller, Bertha Mendez-Guajardo

Abstract


Muscle contraction depends upon the hydrolysis of adenosine triphosphate (ATP), which releases free energy when a phosphate bond is broken. Three systems function to supply energy in the form of ATP to muscle – the phosphagen system, glycolysis and mitochondrial respiration.  During exercise, the phosphagen system is capable of supplying ATP for about 10 – 30 seconds before the muscle cells must revert to glycolysis as a source of ATP.  The purpose of this study was to investigate the phosphagen system and particularly the role that creatine phosphate (CrP) plays in supplying energy in the form of an inorganic phosphate (Pi) to animals supplemented with excess creatine.  Creatine kinase, which enables the hydrolysis of phosphocreatine, to produce ATP and creatine, also serves to reverse this reaction by hydrolyzing ATP to produce ADP and phosphocreatine once again.  By supplementing with creatine, athletes aim to saturate their muscles in order to increase the production of phosphocreatine through the reversed reaction.  In order to mimic the effects of creatine supplementation in athletes, creatine was administered to mice for 12 weeks.  These animals had free access to running wheels.  To assess the effects of creatine supplementation, measurements of force generation, endurance, activity, muscle mass and muscle creatine kinase (CK) levels were taken.  This study found that creatine supplementation lead to a significant increase in force generated during a grip test, but did not affect the endurance or overall activity of the mice.  In addition, soleus muscle mass was significantly increased, while gastrocnemius muscle mass was not affected.  Further investigation of the effect of creatine supplementation on CK protein levels through Western blot analysis found a trend (p = 0.10) toward increased CK in the gastrocnemius of creatine supplemented animals.  Western blot results suggest that grip strength was enhanced due to increased availability of phosphates in Type II muscle fibers, which are more predominant in gastrocnemius versus soleus muscle.  In comparison, Type I fibers are more predominant in the soleus than the gastrocnemius. Since endurance is mostly mediated by Type 1 fibers which have lower creatine content and decreased CK activity, this is likely why the experimental results did not demonstrate an effect on endurance in the creatine supplemented animals.

Keywords


Creatine phosphate, Muscle strength, Phosphagen energy system

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