Creatine began to enter the competitive sports world in 1993, became the most popular ability enhancer in 1994, and was introduced to our country in 1995. Many Chinese athletes use creatine, but very few people truly and systematically understand creatine. This article will review the domestic and foreign research results on creatine, exercise and human health, hoping to enable people to have a correct and comprehensive understanding of creatine, so as to use creatine rationally.
1 Creatine and its metabolism
Creatine, or methacrylate, is a natural substance that is abundantly found in meat and fish foods. Creatine is also a nutrient that naturally exists in our body. It can be synthesized endogenously in the liver, kidney and pancreas from arginine, glycine and methionine as precursors. Therefore, creatine cannot be directly classified as a drug. 95% of creatine is found in skeletal muscles, and the other 5% is found in other parts. The highest content is in the heart, brain and testicles. Semen is full of creatine. A variety of foods contain different concentrations of creatine. The highest content is lean red meat. 1 pound of lean red meat or salmon contains 2g of creatine. Vegetables contain less creatine than edible meat. The creatine stored in these foods will be partially lost during the cooking process. Creatine obtained by the body through food or dietary supplements is easily absorbed from the small intestine into the bloodstream. However, a serving of red meat only contains 1g of creatine, and while taking in creatine, it also brings in a lot of fat. Too high fat and too low sugar in the diet will reduce the uptake of creatine by the muscles and reduce the availability of creatine in the muscles. When dietary supplementation is insufficient, the body's liver, pancreas, and kidneys can also synthesize creatine from arginine, methionine, and glycine. However, relying on these alone cannot achieve the ideal concentration of creatine in the muscles for an active human body. Therefore, high creatine content in muscles can only be achieved by supplementing creatine. The normal human muscle creatine content is 120~125mmolkg dry weight muscle. Supplementing creatine for a short period of time (15~30g per day for 5~7 days) increases total creatine reserves by 15%~30% and creatine phosphate reserves by 10%~40%. It's not possible to determine the exact amount of creatine in someone's muscles. The upper limit of human muscle creatine content is 160mmolkg dry weight muscle. When creatine supplementation reaches this amount, the muscle creatine content will no longer increase. Excess creatine taken in is excreted by the kidneys. Creatine is a small molecular weight substance that is excreted by the kidneys in a diffuse manner without requiring energy. Therefore, creatine supplementation will not cause harm to people without kidney disease.
Recent research shows that when supplementing 20g of creatine per day and supplementing glucose (380g per day) for 5 days, the creatine content in the muscle is 10% higher than that of pure creatine supplementation, that is, it increases from 143mmolkg to 158mmolkg dry muscle. . At the same time, twoWhen used together, the glycogen content is 18% higher than when glucose is used alone. Only 50% of those who used creatine alone had an increase in total muscle creatine greater than 20 mmolkg of dry muscle, while all users of creatine and glucose had an increase in creatine greater than 20 mmolkg of dry muscle. Researchers believe that the increase in muscle uptake of creatine is related to the increase in serum insulin caused by glucose.
2 The effect of creatine on human body activity
Supplementing creatine for a short period of time (15~25g per day, 5~7 days) can increase total creatine by 15%~30% (127~149mmolkg dry weight muscle), and increase creatine phosphate storage by 10%~40% (67~ 91 mmolkg dry weight muscle). The role of increased creatine and creatine phosphate reserves is to maintain ATP levels during high-intensity exercise and promote the resynthesis of creatine phosphate during intermittent periods of repeated high-intensity exercise. Therefore, short-term creatine supplementation can increase maximum work and/or strength by 5% to 15%, increase muscle contraction capacity at maximum force by 5% to 15%, and increase single sprint ability by 5% to 15%. In addition, long-term supplementation of creatine (15g~25g per day for 5d~7d, then 2g~25g per day for 7d~84d) can significantly increase strength, sprinting ability and lean body mass. Another set of experiments by Richard et al. added creatine to a glucose-taurine-electrolyte drink for 28 days on humans engaged in activities (resistance training or flexibility training). The results were an increase in lean body mass and an increase in weightlifting and sprinting abilities. . Grindstaff et al. gave 18 young professional swimmers in the training period creatine (21gd) for 9 days, and maltodextrin for another 9 days as a control. They conducted 3 groups of 100m sprint swimming with 60-second intervals for ability testing. The result is that the first 100m experimental group is faster than the control group; the swimming time of the second 100m experimental group is significantly shortened; the cumulative time of three 100m swimming after taking creatine is shorter than that of the control group. The results show that creatine supplementation for 9 days during the training period can enhance the ability of repeated sprint swimming. Kreider reviewed a large amount of literature and concluded that although there are individual studies that creatine supplementation has no strong effect, most studies indicate that creatine supplementation (20g per day, 5-7 days) increases sprinting ability by 1% to 5%; repeated sprinting The work done can be increased by 15%. He believes this powerful effect is related to the increased amount of creatine uptake by the muscles. In the review, he also mentioned that supplementing creatine for 1 to 2 months during the training period can further improve sprinting ability by 5% to 8% and increase strength by 5% to 15%. Lean body mass increases by 1% to 3%.
The main function of creatine is to increase energy through skeletal muscles, cardiac muscle, smooth muscles, eyes, brain, and nervous system. Because these organs have to work and coordinate activities, increasing the level of creatine in the cells can enhance their ability to exercise. Excess creatine in muscles does not increase muscle quietnessHowever, sufficient creatine in the muscle can ensure the resynthesis of ATP and creatine phosphate consumed during exercise, thereby maintaining the ATP concentration of the muscle during repeated maximum force sprint training, which can minimize local lactic acid in the muscle. generation, allowing the human body to exercise at higher intensity for longer periods of time. This can help the body increase strength, increase work ability, increase muscle size and prevent premature fatigue.
Research shows that creatine can increase the ability of muscle fibers to uptake protein. Actin and myosin are necessary for the contraction of all muscles. So when you increase these contractile proteins, you actually increase the ability of your muscles to engage in physical activity, you'll do more work more of the time, and you'll be stronger. Most studies believe that creatine supplementation mainly enhances exercise capacity during short-term, high-intensity, and repeated exercise. The American College of Sports Medicine states that creatine increases the pool of creatine phosphate to rapidly synthesize ATP. Taking 20-25gd of creatine for 5-7 days as a shock dose, and then continuing to use it as a maintenance dose of 3-5gd will improve the human body's ability to maintain short-distance cycling, sprinting, swimming, high jumping and wrestling. Recent studies have also pointed out that in long-distance running, creatine can also enable athletes to train at a higher intensity than they are accustomed to without fatigue.
3 Creatine changes the body composition of the human body
Recently, more and more research has focused on the anabolic effects of creatine. Most studies believe that short-term creatine supplementation (20-25g per day for 7 days) can increase body weight by 0.7-1.6kg. The reason is that creatine stimulates water retention and/or protein synthesis. Ziegenfuss et al. reported that 5 days of creatine supplementation increased thigh muscle volume by 7%, and intracellular and extracellular water increased by 2% to 3%. Some studies that supplemented creatine for a long period of time (7-140 days) during training also showed that both body weight and lean body mass increased significantly, while the ratio of total water to total body weight did not change. Some researchers hypothesize that creatine first stimulates an increase in intracellular water, increasing the osmotic pressure of cells, and also stimulates protein synthesis. Subsequent increases in lean body mass and strength may be due to increased protein synthesis and/or maintenance of high training volumes that enhance lean tissue growth.
The American College of Sports Medicine states that creatine supplementation will increase body weight slightly (0.5~1kg). The initial weight gain may be due to an increase in overall water content. The positive effects of creatine occur with long-term training. Within 10 to 12 weeks, body weight and lean body mass increase, but body fat percentage does not change.
4 The beneficial effects of creatine on human body fat metabolism and glucose metabolism
Earnest et al. conducted a study on the impact of creatine use on blood lipids. They gave 34 male and female subjects aged 32 to 70 years to take 20g of creatine for 5 days, and then continued to take 10g of creatine for a total of 51 days. Results: Total cholesterol, triglycerides and very low-density lipoprotein were significantly reduced. In addition, the experiment also revealedThe group using creatine now has a tendency to lower blood sugar. This effect of creatine may improve insulin sensitivity, which is beneficial to diabetics in lowering blood sugar. This shows that creatine is likely to lower blood lipids and increase glucose metabolism.
5 Side effects and safety of creatine
Most studies agree that creatine is an effective and safe nutritional supplement. Creatine is an amino acid whose supplementation may promote kidney stress or liver damage. However, there are no reports on significant changes in liver and kidney function caused by creatine supplementation. The experimental results of Sewell et al. show that young and healthy adults take 20g of creatine every day for 5 days. During the period of taking creatine and within 6 weeks after taking it, the use of creatine has no effect on the functions of the kidney, liver and blood system. Any side effects and all test indicators are within the normal range. Mitchell et al studied the safety of creatine. 34 men and women aged 32 to 70 participated in this experiment. 20 subjects took 20g of creatine for 5 days, and then continued to take 10g of creatine for a total of 51 days. The results only showed a slight increase in urea nitrogen (BUN) in women at the 8th week, and a slight increase in creatine phosphate kinase (CPK) in men at the 3rd week. These changes returned to normal levels at 12 weeks. Otherwise, no other changes in the blood tests were seen. In the experiment of Kreidger et al., a group of college football players used a drink containing creatine (creatine 15.75g, added glucose, and sodium taurine sulfate for 28 days while engaging in resistance and agility training. Compared with athletes who did not use creatine, After using creatine, blood tests showed that all indicators and enzymes were within normal ranges, and the use of creatine did not cause any stimulation to the liver. The athletes also did not report any side effects of long-term supplementation.
There are some case reports from coaches that creatine supplementation will increase the incidence of muscle cramps and strains. Regarding the side effects of creatine, Kreider et al. conducted a 28-day experiment using placebo on 84 subjects and creatine on 80 subjects. No side effects of muscle cramps and damage were found in the use of creatine. Muscle cramps in athletes training in hot and humid environments are associated with muscle fatigue and dehydration. Therefore, athletes who use creatine and train in hot environments should pay special attention to fluid replacement. Experiments on giving creatine to humans have been going on for more than a century. Dr. Balsom of Sweden published a review article in 1994 and mentioned: "The best of our knowledge is that the proven side effect of creatine is only an increase in body mass." I suspect that most athletes will happily accept this "side effect".
6 Conclusion
Many exercise-enhancing supplements have come and gone in the past few years, but creatine remains on the health care market and has become one of the most popular muscle-building nutrients. Currently, creatine use is not limited to athletes;Sports, people of all ages, even flying homing pigeons. Since you are going to use creatine, you should have a comprehensive understanding of it.
6.1 Creatine is an effective and safe nutritional supplement.
6.2 Creatine supplementation can increase muscle creatine reserves and promote the resynthesis of creatine phosphate and ATP after muscle contraction, thereby ensuring the energy supply of muscles during high-intensity repeated contractions and improving training effects and exercise capacity.
6.3 Creatine supplementation first stimulates an increase in intracellular water, increasing the osmotic pressure of cells, and also stimulates protein synthesis. Increased protein synthesis and/or heavy training volume lead to increases in lean body mass and strength.
6.4 In order to ensure the effectiveness of creatine and avoid side effects, several principles must be followed:
6.4.1 Strictly control the dose of creatine, that is, the shock dose: 20g per day, taken for 5 to 7 days; the maintenance dose: 2 to 5g per day (5 to 15g has been reported in the literature). Excessive intake of creatine will be excreted by the kidneys and cause waste. Don’t be blindly superstitious about imported creatine. Domestic creatine has the same quality as imported creatine, but the price is cheaper;
6.4.2 Taking sugary drinks while using creatine will help muscles absorb more
More creatine, thereby improving the effect of creatine supplementation;
6.4.3 Athletes who use creatine, especially those training in hot and humid environments, should pay attention to fluid supplements to ensure muscle hydration and prevent muscle spasms and strains.