Creatine and Exercise

Introduction  

Creatine is a naturally occuring dietary compound primarily produced in the liver, but can also be ingested through sustenance or supplementation. Stored predominately in muscular tissue, creatine supplementation possesses documented exercise benefits, particularly related to short, high-intensity bouts.  Evidence suggests that improvements are possible regardless of age or gender.

Positive associations with creatine supplementation include increased strength, lean body mass, and enhanced fatigue resistance.  Creatine supplementation plus resistance training translates into a larger increase in bone mineral density, muscle strength, and lean tissue mass than just resistance training alone.  It has been shown that with higher brain creatine, there comes an improved neuropsychological performance Many athletes utilize creatine for body building or for improving athletic performance, aiding in the worldwide growth in popularity of creatine supplementation.  For older adults, the use of creatine can improve their quality of life and may reduce the disease burden on their cognitive dysfunction. Overall, creatine is a safe and cheap supplement that has both central and peripheral effects for adults. 

Exercise Effects

Creatine supplements can be taken to function as an ergogenice aid during exercise. Creatine supplementation increases the levels of phosphocreatine (PCr) in muslces, which is used by creatine kinase to regenerate Adenosine triphosphate (ATP) in skeletal muscle. Increased levels of PCr improves exercise performance during high intensity exercise and muscular strength and endurance. Research has evaluated the effects of polyethylene glycol (PEG) creatine supplementation taken for a 28 day period to assess its effects on anaerobic capacity. Creatine binds to PEG, which functions as a delivery system and increases the reuptake effeciency and ergogonic effects during exercise. Supplementation with PEG-creatine resulted in improved performance in vertical power, agilityt, and upper-body endurance. Some of these improvements could be due to the shortened muscle relaxation time acquired from the creatine supplementation, which would assist quickly repeated muscle movements. The supplementation also caused an increase in body mass. The improvements generated by PEG-creatine supplementation would be most beneficial for untrained individuals.

Anaerobic Effects

Creatine loading has been evaluated for its effects on anaerobic running capacity (ARC) and body weight changes for males and females. ARC represents the theoretical distance and individual could run using only stored anaerobic energy of ATP and PCr. Creatine loading increases available ATP and PCr for creatine kinase reactions. After creatine loading, males experienced a 23% increase in ARC, but females had no significant changes. This could be due to the higher resting levels of intramuscular creatine in females, which would make them less sensitive to creatine loading. Body weight changes were small in both males and females and were mostly from increased intramuscular water volume.. Therefore, for sports involving running, creatine supplementation can be used to increase anaerobic running capacity in males without the potential to decrease performance from weight gain.

Another study that supports creatine supplementation and improved anaerobic performance focused on young adult males. The participants completed two Windgate Anaerobic tests on the bicycle ergometer with average power and maximum power being measured. The results of the study showed an increase in average power in those who supplemented with 20g of creatine monohydrate per day over a seven day period.

Muscular Strength (short-term)

Creatine's ability to improve the function of the ATP-PC system may improve muscular strength. One study looked at the effects of varying doses of creatine and frequency of resistance training on muscular strength over a six week period.  The participants performed a one-repetition max test (1RM) for upper extremity using a bench press test and one for lower extremeity using a leg press test.  The results showed no improvement in muscular strength following creatine supplementation. Another study examining young adults males to investigate the effects of seven days of creatine-monohydrate loading on muscular strength.  The study used a 1RM bench press and 1RM lower extremity test to measure changes in muscular strength.  The results showed no improvement in strength from creatine supplementation. These two studies revealed insignificant results for the short-term benefits of creatine supplementation on muscular strength.

Creatine Utilization in Rehabilitation

Creatine can be effective in the rehabilitative setting. Researchers have discovered ways to utilize creatine to aide interventions performed in rehabilitative settings. For instance, a study by Eijnde, Urso, Rchter, Greenhaff, & Hespel (2001) conducted a randomized controlled trial with twenty four subjects. All of the subjects were put into an immobilization cast for two weeks and then underwent ten weeks of rehabilitation. Half of the subjects were provided creatine supplements and the other half a placebo. The researchers tested each of the subject's muscle GLUT4 content, muscle glycogen content, and muscle creatine content during immobilization and during rehabilitation. At the end of the study, the researchers concluded that creatine supplementation prevented the downregulation of GLUT4 transporters, maintained muscle glycogen content, and maintained muscle creatine content during immobilization. Creatine supplementation also helped increase muscle GLUT4, muscle glycogen, and muscle creatine levels above baseline after three weeks of rehabilitation. This study is important in the field of rehabilitation by providing evidence that athletes or individuals injured during exercise could shorten recovery time after injury.

Another study related to creatine use during rehabilitation is a randomized controlled trial conducted by Fuld, Kilduff, Neder, Pitsiladis, Lean, Ward, & Cotton (2005). In this study, forty one patients with chronic obstructive pulmonary disease (COPD) were divided into two groups. One group was given a creatine supplement, and one was not. Both of the groups completed several different tests and went through a pulmonary rehabilitation plan. Throughout the intervention, pulmonary function, body composition, muscular strength, exercise capacity, and quality of life were evaluated. At the end of the experiment, the patients ingesting creatine showed improvements in body composition (increase in fat free mass), muscular strength, and quality of life. The results are significant because they suggest patients struggling with COPD may improve peripheral strength, potentially alleviating mortality factors associated with COPD such as muscular atrophy and dysfuntion.

Creatine Utilization in the Elderly Population

The effective use of creatine as an ergogenic aid is well documented in research literature. However, there is less research available on it's use in the elderly population. The research shows that an exercise program coupled with creatine supplementation resulted in increased strength and fat-free mass in both men and women aged over 65 years when compared with exercise alone.  Interestingly enough, there is also sufficient evidence to suggest that supplementing with both creatine and protein in conjunction with exercise provides greater increases in strength and fat-free mass vs. creatine supplementation alone.  Furthermore, creatine appears to be a safe method of increasing strength and fat-free mass in elderly populations. The time frame in which creatine supplements are administered can impact the increases in muscle mass, strength, and performance of older patients .

Side Effects 

Oral creatine supplementation shown evidence of increased efficacy with many different athletic activities. Recently more studies are being done to research the side effects of creatine supplementation with long term use. A critical review of the current data concerning the safety of oral creatine supplementation sheads light on many of the issues of long term use. "In healthy subjects, studies adverse effects have focused on muscle cramping, gastrointestinal symptoms, and renal/hypatic laboratory reults".  Some other less researched effects that have been found were water retention and increased work load on the kidneys.  The formation of formaldehyde is commonly cited as a safety hazard associated with creatine. However, studies show that creatine supplementation does not significantly increase formaldehyde production before and after supplementation.