In the section on alactic anaerobic metabolism, it was seen that creatine is a molecule involved in energy production: once phosphorylated, it reacts with an ADP molecule to form ATP. 

Function

  Although the biological functions of creatine are many, those that have a direct influence on performance are purely related to the role this molecule plays in the production of chemical energy in the absence of oxygen. As around 66% of muscle creatine stores are in a phosphorylated form, theoretically a phosphocreatine-based product would be preferable, but such molecules are almost completely destroyed in the gastrointestinal tract, so one must necessarily opt for non-phosphorylated creatine products. Creatine also has the ability to assist the supply of muscle glycogen. As creatine’s influence on performance only concerns alactacidic anaerobic metabolism, which is known to have great power on the one hand, but low capacity on the other, creatine products are recommended for athletes who have to sustain high-intensity loads for up to ten seconds (possibly repeated between recovery periods).

Negative notes

  Creatine supplements are generally considered safe, although an increased incidence of muscle cramps following creatine administration has been reported under certain circumstances. Apart from this, as well as some hypoglycaemic activity, the only negative note concerns inter-individual sensitivity to creatine. More specifically, in order for creatine supplementation to have a positive impact on performance, it must be such that it causes a joint increase in creatine and phosphocreatine of at least 20mmol per kg of dry muscle (thus neglecting the water mass inside). Unfortunately, regardless of the dosage, this effect cannot be achieved in some people. This inevitably results in a total insensitivity to creatine products. This insensitivity affects 25-30% of individuals. Furthermore, there is an inter-individual sensitivity related to particular factors:

• Tarnopolsky (2000) notes that women are less sensitive than men;
• Rawson (2002) notes that creatine sensitivity tends to decrease with increasing age;
• Muscle fibres are not all the same. They are roughly classified into type I and type II fibres. Type I fibres are more efficient than type II fibres from a purely metabolic point of view, while the latter are more suited to performance where contractility is a priority. In other words, type I fibres are particularly suited to extensive (endurance) performance, while the others are more suited to intensive (strength and power) performance. The distribution of the two fibre types in the musculature is genetically determined and can only be partially modified by training. Well, Syrotuik (2004) notes that the greater the number of type II fibres compared to type I fibres, the greater the athlete’s sensitivity to creatine supplementation;
• With regard to strength performance, Syrotuik (2004) notes that the more experience the athlete has in training this motor skill, the more responsive he or she is to creatine supplementation.

Form and posology

  Creatine products are available on the market in both soluble powder and tablet form. With regard to dosage, research suggests that the best solution is to alternate between a loading phase, with high dosage intake, and a maintenance phase, in which less creatine is taken. With regard to the loading phase, several studies have shown improved endurance performance with intakes of 20-30g/day. More specifically, in a study by Harris (1993), athletes performed four repeated running trials of 300m each with 4 minutes recovery between each trial, or 1000m each with 3 minutes recovery, showing an improvement in both time on the last trial and average time. Soderlung (1994) also shows an improvement in performance due to the intake of creatine in medium and high intensity cycle ergometer tests, protracted for less than 10sec. and with recovery times not exceeding one minute. Finally, in Birch’s study (1994), athletes subjected to 30-second cycle ergometer tests, with a recovery time of 4 minutes between each test, improved their ability to maintain a high pedalling rhythm even in the last few seconds of each test. Unfortunately, however, there are also some studies that do not confirm the effectiveness of creatine: Hultman (1996), in fact, does not find significant improvements in running performance following creatine supplementation. The loading phase should ideally last six days. If this preliminary phase is followed by a period of taking only 2g/day, it is possible to maintain an appreciable creatine level in the muscles for about a month (Redondo, 1994), at the end of which a new loading phase should be carried out. It is desirable to take creatine with meals, especially meat-based meals. It appears, in fact, that this food contains substances that promote creatine retention. On the other hand, it is not advisable to take creatine before or during training: creatine supplements have a slightly hypoglycaemic effect, so taking it when you need blood glucose to be readily utilised by your muscles could deprive them of some of their energy resources. On the other hand, a relatively long period of time is required for the creatine taken to be biologically available to the muscles, so taking it immediately prior to the application of physical load, or during exertion, will be of no greater value than supplementation in another time context.