Figure 2 shows the study protocol. Participants were provided with verbal and written instructions to refrain from any exercise, alcohol, and caffeine in the 48 h before each of the three trial conditions. During this time, physical activity was objectively measured with an Actigraph GT1M accelerometer (Actigraph, Pensacola, FL) worn around the hip during waking hours. Data were recorded in 1-min epochs, with accelerometer counts ≥100/min classified as active time. This was further differentiated as moderate-to-vigorous intensity activity (≥1,952 counts/min) and light-intensity activity (100–1,951 counts/min) (29 (link)). Wear time and activity duration, type, and intensity undertaken during any nonwear periods were recorded in activity diaries. This information, in conjunction with an automated accelerometer wear-time estimation, was used to derive daily wear time.
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.