Glucose tolerance and insulin sensitivity following an one-week volleyball competition.

The purpose of the study was to compare glucose tolerance and insulin sensitivity between trained (TR) and competition (CP) states, in relation to cortisol and testosterone levels. Sixteen highly trained volleyball players voluntarily participated in this study. The first testing session (TR state) occurred 1 week before the start of national level volleyball CP, and the second testing session (CP state) occurred next morning after the 1-week CP. Fasted serum sample was used for measuring cortisol and testosterone. Subjects were then orally challenged with 75 g of glucose solution for determinations of oral glucose tolerance test (OGTT) and insulin response. Under both fasted and glucose challenged conditions, glucose levels of CP were not different from TR state, whereas insulin levels of CP were significantly elevated above TR (50 min: from 78.8 +/- 8.7 to 96.6 +/- 8.1 microU/ml, P < 0.05; 80 min: from 62.8 +/- 7.0 to 82.0 +/- 7.3; P < 0.05). Muscle creatine kinase (CK) level in blood was significantly increased above TR, suggesting greater muscle damage by CP. Serum leptin level, percent fat mass, and body weight were not different between two states. CP significantly increased serum cortisol level without significantly change in testosterone level. The new finding of the study was that volleyball CP reduced the whole-body insulin sensitivity significantly compared to TR state. The greater level of insulin concentration under CP state appears to be associated with elevated serum cortisol level. Despites the benefit of increased physical activity on metabolic function is widely recognized, physiological stress associated with CP can result in attenuation of systemic insulin sensitivity compared TR state.

Characteristics of glycemic control in elite power and endurance athletes.

A previous study has shown that former elite power athletes exhibited significantly greater relative risk in diabetes than that of former elite endurance athletes. It is unknown whether insulin sensitivity in elite young healthy power athletes is lower than that in elite young endurance athletes. This study includes two parts, part I and part II. In the part I of this study, an oral glucose tolerance test was performed in all of the elite juvenile track athlete subjects, specializing either in short-distance racing (jSD, N = 13, aged 12.5 +/- 0.37 years) or in long-distance racing (jLD, N = 13, aged 12.6 +/- 0.42 years). In the part II of this study, we recruited elite adult swimmers and divided them into two groups according to their specialty in swimming race distance: long-distance (aLD, N = 10, age 20.3 +/- 1.32) and short-distance groups (aSD, N = 10, age 20.2 +/- 1.31). Insulin sensitivity was significantly lower in the jSD group than that in the jLD group, as indicated by the area under the curves of insulin and glucose following a 75-g oral glucose load. Fasting plasma LDL-C and total cholesterol levels in the jSD group were significantly greater than those in the jLD group. The result of the part II of this study, similar to the result of the part I, shows that insulin sensitivity in aSD swimmers was significantly lower than that in aLD swimmers. LDL-C, total cholesterol, and triglyceride levels were also found higher in aSD swimmers than in those of aLD swimmers. These new findings implicate that the genetic makeup associated with exceptional power or endurance performance of elite athletes could also reflect on their metabolic characteristics; elite power athletes appear to be more insulin resistant than elite endurance athletes.

Effect of systemic hypoxia on GLUT4 protein expression in exercised rat heart.

Altitude training is a common method used to enhance endurance performance in athletes. We have examined the interactive effect of exercise training and chronic hypoxic on glycogen storage and GLUT4 protein expression in cardiac muscles. Thirty-two male Sprague-Dawley rats were weight balanced and assigned to one of the following four groups: control, exercise, hypoxia, and hypoxia-exercise. Rats with hypoxic treatment (breathing 14% O(2) for 12 hr/d) were exposed under normobaric conditions. The training protocol consisted of swimming for two 3-hr periods per day for 4 weeks. Glycogen content, GLUT4 protein, and mRNA of all rats were determined 16 hr after treatments. Four-week exercise training without hypoxia significantly elevated myocardial glycogen level by 45%. The chronic hypoxic-exercise training elevated the myocardial glycogen level by 67% above control level, significantly greater than the exercise group. Chronic hypoxia, exercise training, and hypoxia-exercise training significantly elevated GLUT4 protein by 40-70% in cardiac muscles. Chronic hypoxia significantly elevates the GLUT1 protein level independent of exercise training. The new finding in this study was that GLUT4 gene expression in cardiac muscle can be stimulated by exercise training with hypoxia treatments. This molecular adaptation appears to be associated with the observed increase in glycogen storage of the muscle.