Participants reported to the laboratory between 0700 and 0800 h, having fasted overnight. A catheter was inserted into an antecubital vein for hourly blood sampling. After the initial blood collection (time point: −2 h), participants remained seated for 2 h to achieve a steady state before the consumption of a standardized test drink (time point: 0 h). The 200-mL test drink consisted of 75 g carbohydrate (100% corn maltodextrin powder; Natural Health, Australia) and 50 g fat (Calogen; Nutricia, Australia). The specific nutritional components were energy, 3,195 kJ; fat, 50.0 g; saturated fat, 5 g; monounsaturated fat, 30.4 g; polyunsaturated fat, 14.3 g; carbohydrate, 75 g; total sugars, 12.8 g; protein, nil; fiber, <1 g; sodium, 46.9 mg; and water, 90 g. The grounds for inclusion of the fat content were based on 1) better simulation of a mixed meal and 2) its influence of slowing the ingested glucose production (gastrointestinal emptying) to spread the plasma glucose and insulin responses over more of the selected 5-h treatment period. Participants were then guided through the respective trial condition protocols for the remaining 5 h. The hourly blood collection was undertaken before activity bouts during the activity days (trial conditions 2 and 3 outlined below). The research staff directly supervised participants throughout each trial to ensure that full compliance with the trial protocols was achieved.
The trial conditions are listed as follows:
Participants watched television or DVDs; read books, magazines, or newspapers; performed light paperwork; or worked on a laptop computer throughout the three conditions. As expected, during the 5-h postprandial period in the moderate-intensity activity breaks condition, the mean ± SE accelerometer-measured time spent in moderate-intensity activity was 24.0 ± 1.8 min compared with 0.6 ± 0.4 min in the light-intensity condition. Activity levels were further monitored at the completion of each activity bout using the Borg RPE scale. The mean ± SE (range: min–max) RPEs during the light-intensity and moderate-intensity activity break conditions were 8 ± 0.4 (6–11) and 12 ± 0.4 (8–14), respectively.