Comparing Simple Insulin Sensitivity Indices to the Oral Minimal Model Postexercise.

PURPOSE

This study aims to establish whether changes in indices of insulin sensitivity (Si) derived from fasting glucose and an oral glucose tolerance test (OGTT) are comparable to Si determined by the oral minimal model (OMM) in response to acute moderate-intensity exercise (MIE) and high-intensity exercise (HIE).

METHODS

Eighteen prediabetic subjects completed three conditions: control (no exercise), ∼ 200 kcal of MIE (∼ 50% of VO2peak), and ∼ 200 kcal of HIE (∼ 80% VO2peak). One hour postexercise (or control), subjects underwent a 75-g OGTT; plasma glucose and insulin were measured to determine Si using several OGTT-based indices (OMM, Belfiore index, Cederholm index, Matsuda index, Gutt index, oral glucose insulin sensitivity index, Stumvoll metabolic clearance rate, Stumvoll insulin sensitivity index, 1/mean OGTT insulin, and 1/insulin incremental area under the curve) and fasting indices (1/homeostatic model assessment for insulin resistance, 1/adipose tissue insulin resistance, 40/fasting insulin, and Quantitative Insulin Sensitivity Check Index). ANOVA and Pearson's correlations were used to examine relationships between changes in Si (ΔSi) among various indices compared to the OMM.

RESULTS

Exercise resulted in a significant increase in Si, according to OGTT-based indices ranging from 11% to 51% (MIE, P < 0.04) and from 8% to 85% (HIE, P < 0.05). Fasting indices showed no change in response to MIE (P > 0.29) and a decrease in Si following HIE (P < 0.001). OGTT-based and fasting indices underpredicted ΔSi-OMM by ∼ 40% and ∼ 90% following MIE and HIE, respectively. ΔSi-OMM following MIE was moderately correlated with ΔSi estimated by OGTT-based indices, but not fasting indices. In contrast, ΔSi-OMM following HIE was not significantly correlated with any Si index.

CONCLUSIONS

Insulin sensitivity increases postexercise, according to most Si models. However, there is high variability between indices under each condition, and these measures only correlate with the OMM following MIE. Caution should be exerted when drawing conclusions about the insulin-sensitizing effects of exercise based on OGTT and fasting indices.