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1.3 Proposed Mechanisms of Action It has been suggested that Cr supplementation
can act through a number of distinct mechanisms.
First, if PCr concentrations are increased in skeletal
muscle, PCr can then aid in the rapid rephosphorylation of adenosine diphosphate (ADP) back to adenosine triphosphate (ATP) by the Cr kinase reaction
Sports Med 2005; 35 (2) The Effects of Creatine in Sport and Exercise during high-intensity, very short duration activities,
especially if the bouts of intense activity are repeated with short rest periods between them.[7,8,14,15]
Examples of this type of activity include sprints,
jumping events and weight lifting. Secondly, it can
enhance the capacity for high-energy phosphate diffusion between the mitochondria and myosin heads,
thus, better enabling the heads to engage in crossbridge cycling and tension maintenance.[7,9,16] Thirdly, Cr can act to buffer pH changes brought about by
an increasing acidosis by utilising the hydrogen ions
during the Cr kinase reaction and the rephosphorylation of ADP to ATP and improve cellular homeostasis.[7,9] Fourthly, declining levels of PCr in the cell
due to the increased need to rephosphorylate ADP
can stimulate phosphfructokinase, the rate-limiting
enzyme for glycolysis, thus increasing the rate of
glycolysis in order to increase the rapid production
of ATP.[7,9] Once again, activities lasting between 10
seconds and 2 minutes would benefit from this
mechanism, i.e. 200m, 400m and 800m sprints.
It has also been suggested that increased concentrations of PCr can be associated with muscle hypertrophy and increased protein synthesis. Cr may
cause an osmotic loading effect resulting in the
movement of extracellular water into the muscle
cell, which is a stimulus for protein synthesis or by
decreasing the rate of protein degradation.
Changes in body mass following Cr ingestion is
somewhat controversial but often it is reported that
significant increases occur. Lastly, Cr has been
suggested to shorten relaxation time during intermittent maximal isometric contraction by facilitating
calcium uptake by the sarcoplasmic...
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