Effect of creatine supplementation on intramuscular TCr, metabolism and performance during intermittent, supramaximal exercise in humans.
Level 3 - non-randomized controlled study
Small non-randomized crossover intervention study with a fixed treatment-washout order
PubMed 8719258 · doi:10.1111/j.1748-1716.1995.tb09988.x
What was done
Six men performed intermittent cycling trials consisting of four 1-minute bouts (with 1-minute rest intervals) followed by a fifth bout to fatigue at 115% or 125% VO2 max. Following three familiarization trials, participants completed a trial after 5 days of creatine monohydrate supplementation (CREAT) and another trial following a 28-day washout period ending with 5 days of placebo (CON). Muscle biopsies were used to assess intramuscular total creatine (TCr), phosphocreatine (PCr), adenine nucleotides, inosine 5'-monophosphate, ammonia, lactate, and glycogen.
What was found
Intramuscular TCr increased significantly (P < 0.05) after creatine supplementation compared with the third familiarization trial and the control trial; TCr levels did not differ between the familiarization and control trials. A significant main effect (P < 0.05) was also observed for elevated PCr in CREAT compared to CON. No significant differences occurred between CREAT and CON for the total adenine nucleotide pool (ATP+ADP+AMP), inosine 5'-monophosphate, ammonia, lactate, or glycogen. Despite higher TCr and PCr, there was no difference in exercise duration to exhaustion in the fifth cycling bout (specific numerical values were not reported in the abstract).
Why it matters
This study shows that while 5 days of creatine loading increases muscle creatine stores and 28 days of washout restores baseline levels, the elevated stores do not enhance performance in intermittent supramaximal cycling bouts lasting several minutes where energy demands rely primarily on pathways other than the creatine kinase system.
Limits
The study is limited by an extremely small sample size (n = 6 men) and a non-randomized, fixed trial order (creatine followed by washout/placebo). The abstract reports no exact numerical values, standard deviations, or effect sizes for metabolic markers or exercise duration.
Cited by
- supports After stopping creatine supplementation, elevated creatine levels take about 4 weeks to return to baseline in skeletal muscle, and an estimated 5 weeks to 3 months in the brain.