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CYCLING PERFORMANCE TIPS

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CREATINE PHOSPHATE


PHYSIOLOGY

ATP (adenosine triphosphate) is the chemical compound which provides the energy to power muscle cell (actin-myosin fibers) contraction. A single ATP molecule contains an amino acid base (adenosine), a sugar (ribose) and three phosphate groups. The chemical energy of the ATP molecule is stored in the phosphate groups, and when these high energy phosphate bonds are cleaved or broken during the processes of cellular metabolism, the energy is then available for muscle contraction and other vital cellular functions.

However the cellular storage capacity for ATP is limited, and at maximum work levels ATP stored in the muscle is depleted within several seconds. To sustain physical activity, the cell must continually resynthesize ATP (which is the ONLY molecule able to provide energy to the muscle fibers to power muscle contraction). ATP is resynthesized via one of three metabolic pathways depending on the degree and duration of the physical activity.

The preferred path involves the breakdown of creatine phosphate (CP) - another high energy, phosphate bearing molecule - to supply the chemical energy to resynthesize ATP. Like ATP, CP is also stored in finite amounts in the cell and provides at most an additional 5 to 10 seconds of energy which limits its usefulness to sprint type activities. Once CP has been exhausted, the cell uses two slightly slower metabolic pathways to resynthesize ATP - one is oxygen dependent (aerobic) and the other is not (anaerobic).

Muscle cell ATP is resynthesized from CP at 4 to 8 times the maximal rate from aerobic pathways. This explains why performance in sprint activities of 5 to 20 second duration is positively correlated with muscle CP levels. For sprints of longer duration, the slower, but higher capacity aerobic and anaerobic pathways then take over to resupply ATP. Examples of sprint activities that benefit from high cell AP levels are weightlifting, field events, short track events (100 meter dash), baseball, and volleyball . For sustained muscle activity of more than 10 to 20 seconds duration, and to replenish both CP and ATP, the cell relies on aerobic metabolism.

Creatine is an amino acid occuring naturally in fish and meat, and is found in skeletal muscle, heart, brain, retina, testes and the uterus. Normally less than 1 gram per day is supplied by the diet and another gram is synthesized (mainly by the kidneys). Synthesis is the only source for vegetarians and suggests a role for creatine supplementation in this group of athletes. Creatine is eliminated through the kidneys, and there is concern that high doses might potentially injure the kidneys. However at the doses mentioned below, no adverse affects have been proven.

Demant TW and Rhodes EC (Sports Med 1999 Jul;28(1):49-60) published a nice review on creatine. To quote "While creatine has been known to man since 1835, when a French scientist reported finding this constitutent of meat, its presence in athletics as a performance enhancer is relatively new. Creatinine is synthesised from the amino acids glycine, arginine and methionine in the kidneys, liver and pancreas, and is predominantly found in skeletal muscle, where it exists in 2 forms. Approximately 40% is in the free creatine form (Crfree), while the remaining 60% is in the phosphorylated form, creatine phosphate (CP). The daily turnover rate of approximately 2 g per day is equally met via exogenous intake and endogenous synthesis. Although creatine concentration (Cr) is greater in fast twitch muscle fibres, slow twitch fibres have a greater resynthesis apability due to their increased aerobic capacity. There appears to be no significant difference between males and females in Cr, and training does not appear to effect Cr. Creatine supplementation of 20 g per day for at least 3 days has resulted in significant increases in total Cr for some individuals but not others, suggesting that there are 'responders' and 'nonresponders'. These increases in total concentration among responders is greatest in individuals who have the lowest initial total Cr, such as vegetarians. Increased concentrations of both Crfree and CP are believed to aid performance by providing more short term energy, as well as increase the rate of resynthesis during rest intervals. Creatine supplementation does not appear to aid endurance and incremental type exercises, and may even be detrimental. Studies investigating the effects of creatine supplementation on short term, high intensity exercises have reported equivocal results, with approximately equal numbers reporting significant and nonsignificant results. The only side effect associated with creatine supplementation appears to be a small increase in body mass, which is due to either water retention or increased protein synthesis."

Supplements of creatine will increase muscle cell CP levels. To quote the abstract of one study "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 hen 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." If you decide to give it a try, at a dosage of 15 to 20 grams per day for a loading period of 7 days and then a maintenance of 3 to 5 grams per day, the cost of a creatine supplementation program is about 50-70 cents a day.

Is there any benefit to ingesting more than 20 grams per day initially? Casey A and Greenhaff PL (Am J Clin Nutr 2000 Aug;72(2 Suppl):607S-17S) report that "ingestion of creatine monohydrate at a rate of 20 g/d for 5-6 d was shown to increase the total creatine concentration of human skeletal muscle by approximately 25 mmol/kg dry mass, some 30% of this in phosphorylated form as phosphocreatine. However, there is no evidence that increasing intake > 20-30 g/d for 5-6 d has any additional effect on creatine uptake or performance." Another interesting finding was that those already on a high creatinine diet will have decreasing benefits from these supplements. " In individuals in whom the initial total creatine concentration already approached 150 mmol/kg dry mass, neither creatine uptake nor an effect on phosphocreatine resynthesis or performance was found after supplementation." And chronic oral supplements may decrease the level of the cell wall transport protein responsible for moving creatine from the blood into the cell, thus minimizing benefits with time (Guerrero-Ontiveros ML, Wallimann T Mol Cell Biochem 1998 Jul;184(1-2):427-37)

There is evidence that carbohydrate supplementation will improve the benefits of a creatine supplementation program. Muscle biopsy, urine, and plasma samples were obtained from 24 males before and after ingesting 5 g Cr in solution (group A) or 5 g Cr followed,30 min later, by 93 g simple CHO in solution (group B) four times each day for 5 days. Supplementation resulted in an increase in muscle phosphocreatine (PCr), Cr, and total creatine (TCr; sum of PCr and Cr) concentration in groups A and B, but the increase in TCr in group B was 60% greater than in group A (P < 0.01). There was also a corresponding decrease in urinary Cr excretion in group B (P < 0.001). This again supports the importance of adequate carbohydrates in any dietary training program.

Higher muscle CP levels also improve performance in repetitive sprint events and activities that involves several heats or sets. Presumeably the additional muscle CP, recharged from the aerobic and anaerobic pathways, aid in a rapid resynthesis of ATP.

The most recent summary of creatine as a supplement is found in an American College of Sports Medicine roundtable on the physiological and health effects of oral creatine supplementation (Med Sci Sports Exerc 2000 Mar;32(3):706-17). To excerpt: "Creatine (Cr) supplementation has become a common practice among professional, elite, collegiate, amateur, and recreational athletes with the expectation of enhancing exercise performance. Research indicates that Cr supplementation can increase muscle phosphocreatine (PCr) content, but not in all individuals. A high dose of 20 g x d(-1) that is common to many research studies is not necessary, as 3 g x d(-1) will achieve the same increase in PCr given time. Coincident ingestion of carbohydrate with Cr may increase muscle uptake; however, the procedure requires a large amount of carbohydrate. Exercise performance involving short periods of extremely powerful activity can be enhanced, especially during repeated bouts of activity. This is in keeping with the theoretical importance of an elevated PCr content in skeletal muscle. Cr supplementation does not increase maximal isometric strength, the rate of maximal force production, nor aerobic exercise performance. Most of the evidence has been obtained from healthy young adult male subjects with mixed athletic ability and training status. Less research information is available related to the alterations due to age and gender. Cr supplementation leads to weight gain within the first few days, likely due to water retention related to Cr uptake in the muscle. Cr supplementation is associated with an enhanced accrual of strength in strength-training programs, a response not independent from the initial weight gain, but may be related to a greater volume and intensity of training that can be achieved. There is no definitive evidence that Cr supplementation causes gastrointestinal, renal, and/or muscle cramping complications. The potential acute effects of high-dose Cr supplementation on body fluid balance has not been fully investigated, and ingestion of Cr before or during exercise is not recommended. There is evidence that medical use of Cr supplementation is warranted in certain patients (e.g.neuromuscular disease); future research may establish its potential usefulness in other medical applications. Although Cr supplementation exhibits small but significant physiological and performance changes, the increases in performance are realized during very specific exercise conditions. This suggests that the apparent high expectations for performance enhancement, evident by the extensive use of Cr supplementation, are inordinate."

BICYCLING SPECIFIC STUDIES

There have been at least 8 good studies on the effects of creatine supplementation on cycling performance - and with conflicting results. A quick review of the literature turned up 9 contolled studies with 4 indicating a positive effect, and 5 demonstrating no benefit.

Although there is tantalizing evidence that creatine supplements may benefit single and repetitive sprint performance in events of 15 to 30 seconds duration, this is far from proven. And there is no evidence to support its use in cycling events lasting more than a minute.

THE BOTTOM LINE (FACT VS FICTION)


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