Creatine Monohydrate

PCr’s major cellular function is to maintain metabolic flux during the early onset of exercise and high-intensity work performance. Given the observed greater ATP production associated with PCr, and coupled with the increase in PCr associated with creatine supplementation, the potential for an increase in anaerobic work output is fully justifiable. Moreover, the maintenance of PCr concentrations appears to correlate well with the development of fatigue in that its decrease is associated with a decline in muscular force. Infante et al. showed a direct relationship between external work and PCr breakdown in the frog rectus abdominis muscle. Spande and Schottelius also showed a direct relationship between force production and PCr stores in isolated mouse soleus muscle that was tetanically stimulated. In this model, they observed a decline in PCr that was directly proportional to the development and maintenance of isometric tetanic force.

In humans, Hirvonen et al. concluded that the slowing of running speed during maximal work efforts is related to a decline in the energy production brought forth from ATP and PCr. This effect may be a result of muscle fiber type differences in the endogenous stores of each substrate. This premise is supported by the observations of others who have noted that type II muscle fibers possess higher initial levels of PCr and, consequently, greater rates of PCr usage than do type I muscle fibers during high-intensity exercise. PCr and glycogen recovery also appears to be slower in type II fibers following high-intensity exercise. Moreover, PCr resynthesis during recovery has been shown to be an oxygen-dependent process that exhibits a two-component or biphasic pattern. The first (fast component) has a half-time of approximately 22 seconds, whereas the second (slow component) is longer than 170 seconds. During continuous or intermittent high-intensity exercise, the resynthesis rate of PCr plays an important role in the force capabilities that active muscle can generate owing to the heavy reliance on PCr and ATP.

When PCr levels are not given adequate recovery time, performance is impaired and power output is decreased Conversely, when recovery is prolonged, increased PCr concentration is correlated with greater power output during consecutivecycle ergometer sprints when rest periods of either 90 or 180 seconds are allowed. Thus, the possibility of creatine supplementation increasing PCr recovery is important because it is the recovery of PCr following high-intensity exercise that allows athletes to continue high-intensity activity more effectively. If it is possible to increase the rate of resynthesis and PCr storage capacity through supplementation, then the use of creatine has a valid physiological base from which to assess utility