Effects of Varying Physical Activity Level on Glucose Tolerance Testing

Abstract

The oral glucose tolerance test (OGTT) is a commonly used method for the diagnosis of insulin resistance. Currently the only level of control prior to an OGTT is an 8-10 hour fast. Physical activity is known to influence glucose uptake kinetics. Thus, our PURPOSE was to determine if varying the level of physical activity, the day prior to an OGTT, influenced the blood glucose and insulin responses to an OGTT. We hypothesized that higher levels of physical activity the day prior to an OGTT would result in attenuated blood glucose and insulin responses to an OGTT. METHODS: Ten healthy adults (6 m/4 f; age = 21.5±0.3y; BMI= 24±5 kg·m-2) participated in three OGTT trials the morning after performing 50%, 100%, or 150% of their habitual physical activity in randomized order. Habitual physical activity as average steps/day (12,318±1310 steps·day-1) was determined using 7-day pedometery. Pedometers were worn for 24 hrs prior to each OGTT trial and used to confirm steps·day-1 for the 50%, 100%, and 150% conditions. Trials were separated by at least one week and subjects were asked to follow a similar diet the day prior to each OGTT trial. For each OGTT trial, plasma glucose and insulin were measured after an overnight fast and at 30 min intervals for two hours following ingestion of the glucose beverage (1-gram glucose·kg-1 body mass). Area under the curve (AUC) for glucose and insulin for each OGTT was calculated using the trapezoidal method. Between trial differences for these variables were analyzed using a general linear model with repeated measures. Significance was set to p< 0.05. RESULTS: Subjects successfully achieved the desired percentage of habitual steps prior to each trial: 52±1%, 98±2%, and 146±3%. Fasting plasma glucose (50%: 95±2 mg·dl-1; 100%: 91±2 mg·dl-1; 150%: 91±2 mg·dl-1), glucose AUC (50%: 12,932±769 mg·min·dl-1; 100%: 13,239±1,008 mg·min·dl-1; 150%: 13,016±471 mg·min·dl-1), and insulin AUC (50%: 5,562±1810 μIU·min·ml-1; 100%: 5181±1839 μIU·min·ml-1; 150%: 4735±1776 μIU·min·ml-1) did not differ between trials. CONCLUSIONS: Our data suggests that varying the physical activity level (from 50 to 150% of habitual activity) the day prior to an oral glucose tolerance test does not influence the blood glucose or insulin responses to this commonly utilized diagnostic test.