Influence of Caffeine on Serum Substrate Changes During Running in Trained and Untrained Individuals

摘要

Previous research has indicated that caffeine (CAF) increases the mobilization and metabolism of free fatty acids (FFA) during prolonged exercise while sparing muscle glycogen. The purpose of this study was to examine the effect of two dosages of CAF on serum substrates in trained (T) and untrained (UT) subjects. In a double blinded, cross-over design, 5 T subjects (V02 max= 62.4 + or - 3.0 ml/kg/min) and 5 UY subjects (V02 max= 46.5 + or - 5.1 ml/kg/min) ran for 1 hr in 3 separate sessions, 1 h after ingestion of a beverage containing either 0, 5 or 9 mg/kg body weight of anhydrous caffeine. Initial exercise intensities were 59% V02 max (T) or 61% V02 max (UT). Blood samples were collected from an indwelling catheter just prior to the run, and at min 5, 10 and every 10 min thereafter. Serum glycerol levels did not differ following CAF ingestion in T or UT as compared to the placebo, through a trend toward higher levels was observed with CAF. Serum FFA increased progressively during the exercise period; however there were no differences (p >0.05) associated with CAF in either T or UT. Serum glucose decreased in the UT during the placebo session and increased in the T during the CAF sessions. Blood lactates were significantly elevated (p <0.05) in the UT in both the 5 mg/kg (2.36 - 2.77 mmo1es/1) and 9 mg/kg (2.38 - 2.68 mmo1/1) dosages as compared to the placebo (1.17 -1.60 mmo1/1); however this CAF effect on lactate values was not seen in the T.