The Effect of Two Different Creatine Formulations on Upper and Lower Body Muscular Strength and Endurance in Resistance Trained Men
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Date
2012-03-28Author
Statz, Stephen J.
Eckerson, Joan M.
Bull, Anthony J.
Moore, Geri A.
Yee, Jennifer C.
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Show full item recordAbstract
Creatine (CR; α-methylguanidinoacetic acid) is a
nitrogenous compound synthesized in the liver and
pancreas from the amino acids arginine, methionine,
and glycine. Dietary sources of CR include meats and
fish, however, large amounts must be consumed to
obtain 1-2 gram quantities (1,4,5). In skeletal muscle,
CR is primarily stored as free CR and
phosphocreatine (PC), a high energy compound that
serves as the primary fuel reserve for the re-synthesis
of adenosine triphosphate (ATP) during and following
intense exercise. Therefore, rapid depletion of
muscle PC is believed to be a limiting factor when
performing maximal anaerobic work.
Several studies have shown that CR loading (20 g·d-1)
for 5-7 days increases intramuscular stores of PC by
10 – 20% which, in turn, accelerates the rate of ATP
re-synthesis (1,3,4). Therefore, dietary CR
supplementation may provide a greater stimulus for
training by reducing the recovery time between
successive bouts of exercise, which allows for greater
overload resulting in increases in muscle strength,
size (hypertrophy), and myosin heavy chain
expression in type II fibers (1,3,4). A considerable
number of studies have reported that short-term CR
supplementation improves maximal strength and
power (5-15%), work performed during sets of
maximal effort muscle contractions (5-15%), single
effort sprint performance (1-5%), and work
performed during repetitive sprint performance (5-
15%) (1,2,3,4).
Most CR products contain a considerable amount of
dextrose (sugar), since early research suggested that a
large insulin spike enhanced CR uptake into muscle
(2). However, a more recent study (5) found that CR
uptake is dependent upon sodium, not insulin. This
led to the formulation of products that contain higher
amounts of sodium and no dextrose; therefore, these
products are also Calorie free. Few studies have
compared the efficacy of these ‘sugar free’ CR
products to more traditional formulations that include
dextrose. Therefore, the purpose of this study was to
compare the effect of two different CR formulations
on upper and lower body strength and muscular
endurance following 5 d of loading in resistance
trained men.