Creatine supplements

Abstract: 1. The present study was undertaken to test whether creatine given as a supplement to normal subjects was absorbed, and if continued resulted in an increase in the total creatine pool in muscle. An additional effect of exercise upon uptake into muscle was also investigated. 2. Low doses (1g of creatine monohydrate or less in water) produced only a modest rise in the plasma creatine concentration, whereas 5g resulted in a mean peak after 1h of 795 (SD 104) mumol/l in three subjects weighing 76-87 kg. Repeated dosing with 5g every 2h sustained the plasma concentration at around 1000 mumol/l. A single 5g dose corresponds to the creatine content of 1.1 kg of fresh, uncooked steak. 3. Supplementation with 5g of creatine monohydrate, four or six times a day for 2 or more days resulted in a significant increase in the total creatine content of the quadriceps femoris muscle measured in 17 subjects. This was greatest in subjects with a low initial total creatine content and the effect was to raise the content in these subjects closer to the upper limit of the normal range. In some the increase was as much as 50%. 4. Uptake into muscle was greatest during the first 2 days of supplementation accounting for 32% of the dose administered in three subjects receiving 6 x 5g of creatine monohydrate/day. In these subjects renal excretion was 40, 61 and 68% of the creatine dose over the first 3 days. Approximately 20% or more of the creatine taken up was measured as phosphocreatine. No changes were apparent in the muscle ATP content.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract: The effect of dietary creatine and supplementation on skeletal muscle creatine accumulation and subsequent degradation and on urinary creatinine excretion was investigated in 31 male subjects who ingested creatine in different quantities over varying time periods. Muscle total creatine concentration increased by approximately 20% after 6 days of creatine supplementation at a rate of 20 g/day. This elevated concentration was maintained when supplementation was continued at a rate of 2 g/day for a further 30 days. In the absence of 2 g/day supplementation, total creatine concentration gradually declined, such that 30 days after the cessation of supplementation the concentration was no different from the presupplementation value. During this period, urinary creatinine excretion was correspondingly increased. A similar, but more gradual, 20% increase in muscle total creatine concentration was observed over a period of 28 days when supplementation was undertaken at a rate of 3 g/day. In conclusion, a rapid way to "creatine load" human skeletal muscle is to ingest 20 g of creatine for 6 days. This elevated tissue concentration can then be maintained by ingestion of 2 g/day thereafter. The ingestion of 3 g creatine/day is in the long term likely to be as effective at raising tissue levels as this higher dose.

Abstract: Biopsy samples were obtained from the vastus lateralis muscle of eight subjects after 0, 20, 60, and 120 s of recovery from intense electrically evoked isometric contraction. Later (10 days), the same procedures were performed using the other leg, but subjects ingested 20 g creatine (Cr)/day for the preceding 5 days. Muscle ATP, phosphocreatine (PCr), free Cr, and lactate concentrations were measured, and total Cr was calculated as the sum of PCr and free Cr concentrations. In five of the eight subjects, Cr ingestion substantially increased muscle total Cr concentration (mean 29 +/- 3 mmol/kg dry matter, 25 +/- 3%; range 19-35 mmol/kg dry matter, 15-32%) and PCr resynthesis during recovery (mean 19 +/- 4 mmol/kg dry matter, 35 +/- 6%; range 11-28 mmol/kg dry matter, 23-53%). In the remaining three subjects, Cr ingestion had little effect on muscle total Cr concentration, producing increases of 8-9 mmol/kg dry matter (5-7%), and did not increase PCr resynthesis. The data suggest that a dietary-induced increase in muscle total Cr concentration can increase PCr resynthesis during the 2nd min of recovery from intense contraction.

Abstract: 1. The present experiment was undertaken to investigate the influence of oral creatine supplementation, shown previously to increase the total creatine content of human skeletal muscle (Harris RC, Soderlund K, Hultman E. Clin Sci 1992; 83: 367–74), on skeletal muscle isokinetic torque and the accumulation of plasma ammonia and blood lactate during five bouts of maximal exercise. 2. Twelve subjects undertook five bouts of 30 maximal voluntary isokinetic contractions, interspersed with 1 min recovery periods, before and after 5 days of placebo (4 × 6 g of glucose/day, n = 6) or creatine (4 × 5 g of creatine plus 1 g of glucose/day, n = 6) oral supplementation. Muscle torque production and plasma ammonia and blood lactate accumulation were measured during and after exercise on each treatment 3. No difference was seen when comparing muscle peak torque production during exercise before and after placebo ingestion. After creatine ingestion, muscle peak torque production was greater in all subjects during the final 10 contractions of exercise bout 1 ( P <0.05), throughout the whole of exercise bouts 2 ( P <0.01), 3 ( P <0.05) and 4 ( P = 0.057) and during contractions 11–20 of the final exercise bout ( P <0.05), when compared with the corresponding measurements made before creatine ingestion. Plasma ammonia accumulation was lower during and after exercise after creatine ingestion. No differences were found when comparing blood lactate levels. 4. There is evidence to suggest that the decrease in the degree of muscle torque loss after dietary creatine supplementation may be a consequence of a creatine-induced acceleration of skeletal muscle phosphocreatine resynthesis. It is postulated that an increased availability of phosphocreatine would maintain better the required rate of ATP demand during contraction. This is supported by the observed lower accumulation of plasma ammonia during exercise after creatine ingestion.