The effects fibers of creatine in muscle
Train for extended periods of time leads to a depletion of glycogen reserves and phosphocreatine (the form in which the creatine is stored) in the skeletal muscles. Previous research suggest that the depletion of reserves of creatine is in the slow-twitch muscle fibers (type 1) that fast (type 2) is due to depletion of glycogen, with the consequent fatigue process. However, no researcher has ever bothered to determine the concentrations of glycogen in different muscle fibers.
In order to examine the changes that occur in the creatine and glycogen during a submaximal training, British researchers did male runners run 6 to 70% of VO2max. They were also made of muscle biopsies (tissue samples): at rest, after 10 minutes of training and once you reach the point of exhaustion. During the first 10 minutes of training, the process of demolition of glycogen was similar for all the muscle fibers, while only those with type 2 used significantly phosphocreatine stores. At the time of fatigue, creatine levels proved to be similar for both the fibers of type 1 and type 2; glycogen, however, was exhausted only in the muscle fibers of type 1. The authors of the study found a strong correlation between the use of creatine and glycogen in the fibers of type 1 (slow-twitch), but not in those with type 2 (fast twitch).
Based on the findings, the researchers concluded that the energy shortage is of type 1 fibers, but not type 2, to contribute to the process of fatigue during a workout submaximal and that, moreover, creatine operates differently in the slow-twitch fibers than fast twitch. An observation of this kind reflects as previously noted, since, in the course of a submaximal exercise, the body uses mainly type 1 fibers, also known as fiber length. A higher intensity training, such as weight training, calls into action the type 2 fibers, especially when you are using heavy loads.