The Effect of Two Different Creatine Formulations on Upper and Lower Body Muscular Strength and Endurance in Resistance Trained Men

Abstract

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.