Determining related work-to-rest ratios following a maximal effort isokinetic leg extension bout in trained and untrained males : a double-blind creatine/placebo controlled study.




Parker, Adam G.

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Purpose: A single 30 second bout of high intensity isokinetic exercise is capable of depleting available skeletal muscle Phosphocreatine (PCr) and adenosine triphosphate (ATP). Within several minutes the body is able to replenish those stores to facilitate further muscular activity. There have been suggested work-to-rest ratios to allow for the optimal recovery period to achieve repletion of the intramuscular PCr and ATP. This study attempted to determine how training status and supplementation with creatine monohydrate (CM) may affect this process. Methods: Subjects in the CM group consumed 20 g of CM (four 5 g doses/day), while subjects in the placebo group consumed 20 g of dextrose (four 5 g doses/day). Five (pre-supplementation, pre-exercise, immediate post exercise, 3 min. post exercise, and 5 min. post exercise) muscle samples were taken from the vastus lateralis of the dominant leg of 32 males [16 resistance trained (8 each receiving CM or placebo), 16 untrained (8 each receiving CM or placebo)]. Samples were measured for Cr, PCr, ATP, glycogen, and lactate, and TCr was calculated by adding Cr and PCr at all time points. Blood lactate was measured via finger prick prior to and 5 minutes after the exercise bout. Results: Subjects consuming CM increased muscle total creatine content by 10.2%. Neither CM supplementation nor resistance training status significantly affected PCr or ATP repletion rates. Trained subjects had significantly (p >.05) higher muscle glycogen content. Trained individuals maintained non-significantly higher muscle ATP and PCr after and at all time points during recovery from the exercise bout compared to untrained individuals. At both 3 and 5 minutes after exercise, none of the groups were able to fully restore resting levels of muscle ATP or PCr. Conclusions: The results indicate that CM and training status did not significantly enhance repletion rates of muscle ATP or PCr. Further, 5 minutes of rest was not long enough to fully recover muscular ATP and PCr content.



Creatine supplementation., Exercise metabolism., Resistance training.