Effects of repeated creatine supplementation on muscle, plasma, and urine creatine levels.
Level 4 - case-series / case-control
Single-subject case study (n=1)
PubMed 14971966 · doi:10.1519/1533-4287(2004)018<0162:eorcso>2.0.co;2
What was done
A 32-year-old resistance-trained male ingested 20 g/day of creatine for 5 days across 2 supplementation bouts separated by a 30-day washout period. Muscle phosphocreatine was measured before and after each bout. On day 1 of each bout, blood samples were collected before and hourly for 5 hours following ingestion of 5 g of creatine for pharmacokinetic analysis. Twenty-four-hour urine collections were conducted before and throughout each 5-day supplementation period.
What was found
Muscle phosphocreatine increased 45% following the first bout, decreased 22% during the 30-day washout, and increased 25% following the second bout. Muscle phosphocreatine prior to bout 2 remained 23% higher than pre-bout 1 baseline, while final postsupplementation levels were similar between bouts. Plasma pharmacokinetic parameters showed no meaningful differences between bouts. Total urinary creatine losses during supplementation were 63.2 g in bout 1 and 63.4 g in bout 2. The elevated muscle phosphocreatine throughout the washout period coincided with a sustained 2.0 kg increase in body mass.
Why it matters
This case study indicates that a standard 30-day washout period may not be long enough for muscle phosphocreatine stores or body mass to return to baseline after creatine loading. This has direct practical implications for crossover trial designs and athletic cycling regimens.
Limits
The study is an n=1 case report in one male participant, preventing statistical analysis or generalization to broader populations. Dietary intake controls, physical performance tests, and intermediate muscle biopsies during the washout phase were not reported in the abstract.
Cited by
- context 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.