Schoch et al. JISSN 3(1):60-66, 2006--06/23/2006
Abstract
Schoch, R.D., D. Willoughby, M. Greenwood. The regulation and expression of the creatine transporter: a brief review of creatine supplementation in humans and animals. Journal of the International Society of Sports Nutrition. 3(1): 60-65, 2006.
RESPONDERS VS. NONRESPONDERS
Most studies have reported an increase in
intramuscular creatine levels with
supplementation; however, variability does
exist. This poses the possible scenario of
“responders†versus “nonresponders†to creatine
supplementation. It is hypothesized that much
of this variability lies within the regulation and
activity of the creatine transporter.
Unfortunately, most of the limited creatine
supplementation research conducted
investigating the expression of CreaT has been
through animal models, as previously noted.
Greenhaff et al observed that approximately 20-30%
of participants following a creatine loading
regime did not respond with an increase in
intracellular creatine 24 . This was defined as
resting total muscle creatine levels less than
10mmol/kg following a 5 day creatine loading
phase at 20g/d. Responders were then classified
as achieving a 20mmol/kg increase following
the loading phase. Recently, Syrotuik and Bell 25 conducted a descriptive profile of individuals
portraying Greenhaff’s classification of
“responder†and “non-responderâ€Â
characteristics. Results of this study concluded
that the responders generally:
1) possessed a
lower initial quantity of intramuscular creatine
and were able to absorb and take up a greater
amount through supplementation; 2) had a
greater percentage of type II fibers; 3) had a
greater fiber cross sectional area; and 4)
possessed more fat-free mass. This data
suggests that an individual’s biological profile
may partially determine the efficacy of a
creatine supplementation protocol.