Comparison of glucose tolerance tests to detect the insulin sensitizing effects of a bout of continuous exercise

The aim of the present study was to determine which of the available glucose tolerance tests (oral (OGTT) vs. intravenous (IVGTT)) could more readily detect the insulin sensitizing effects of a bout of continuous exercise. Ten healthy moderately fit young men ((V) overdotO(2peak) of 45.4 +/- 1.8 mL.kg(-1).min(-1); age 27.5 +/- 2.7 yr) underwent 4 OGTT and 4 IVGTT on different days following a standardized dinner and overnight fast. One test was performed immediately after 55 min of cycle-ergometer exercise at 60% (V) overdotO(2peak). Insulin sensitivity index was determined during a 50 min IVGTT according to Tura (C-ISI) and from a 120 min OGTT using the Matsuda composite index (M-ISI). After exercise, M-ISI improved 29 +/- 10% without reaching statistical significance (p = 0.182) due to its low reproducibility (coefficient of variation 16 +/- 3%; intra-class reliability 0.846). However, C-ISI significantly improved (50 +/- 4%; p < 0.001) after exercise showing better reproducibility (coefficient of variation 13 +/- 4%; intra-class reliability 0.955). Power calculation revealed that 6 participants were required for detecting the effects of exercise on insulin sensitivity when using IVGTT, whereas 54 were needed when using OGTT. The superior response of C-ISI compared with MISI suggests the preferential use of IVGTT to assess the effects of exercise on insulin sensitivity when using a glucose tolerance test.