Insulin resistance and glucose intolerance typically associated with physical inactivity and obesity in older individuals. In this study, seventeen adolescent swimmers were divided into two groups: pre-pubertal state (PRE) and post-pubertal state (POST) according to the development of secondary sexual characteristics. Significantly lower fasting blood growth hormone and higher triiodothyronine concentration were observed in the subjects in POST group than PRE group. Oral glucose tolerance test (OGTT) was utilized to determine the capability of in vivo glucose clearance in these adolescent swimmers. The blood glucose and plasma insulin concentrations were measured before (fasting or 0 min) and after (30 min, 50 min, and 80 min) a 75-gram of glucose ingestion. The subjects in POST group displayed a higher glucose concentration than PRE group at 30 min after the glucose challenge (75±5.53 vs. 62±1.63 mg/dl, p<0.05). The insulin concentration between two groups in all time points was not significantly different. These results indicate that the subjects in the PRE group, even with less fat-free mass, displayed a significantly better insulin sensitivity for the whole-body glucose uptake than the POST group. Total blood cholesterol level of the subjects was significantly higher in the POST group than the PRE group. These results suggest that the spontaneous reduction in the whole-body insulin sensitivity for glucose disposal is occurred during the adolescent growth spurt. The higher plasma total cholesterol concentration seems to be associated with this change. It is known that skeletal muscle is the major site for the in vivo insulin-sensitive glucose disposal. Additionally, fast twitch is more insulin resistant than the slow twitch. We suggest that the muscle fiber type transformation induced by the endocrinological changes during the adolescence growth spurt may affect the in vivo insulin sensitivity and glucose tolerance.
Insulin resistance and glucose intolerance typically associated with physical inactivity and obesity in older individuals. In this study, seventeen adolescent swimmers were divided into two groups: pre-pubertal state (PRE) and post-pubertal state (POST) according to the development of secondary sexual characteristics. Significantly lower fasting blood growth hormone and higher triiodothyronine concentration were observed in the subjects in POST group than PRE group. Oral glucose tolerance test (OGTT) was utilized to determine the capability of in vivo glucose clearance in these adolescent swimmers. The blood glucose and plasma insulin concentrations were measured before (fasting or 0 min) and after (30 min, 50 min, and 80 min) a 75-gram of glucose ingestion. The subjects in POST group displayed a higher glucose concentration than PRE group at 30 min after the glucose challenge (75±5.53 vs. 62±1.63 mg/dl, p<0.05). The insulin concentration between two groups in all time points was not significantly different. These results indicate that the subjects in the PRE group, even with less fat-free mass, displayed a significantly better insulin sensitivity for the whole-body glucose uptake than the POST group. Total blood cholesterol level of the subjects was significantly higher in the POST group than the PRE group. These results suggest that the spontaneous reduction in the whole-body insulin sensitivity for glucose disposal is occurred during the adolescent growth spurt. The higher plasma total cholesterol concentration seems to be associated with this change. It is known that skeletal muscle is the major site for the in vivo insulin-sensitive glucose disposal. Additionally, fast twitch is more insulin resistant than the slow twitch. We suggest that the muscle fiber type transformation induced by the endocrinological changes during the adolescence growth spurt may affect the in vivo insulin sensitivity and glucose tolerance.
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