Single bouts of exercise reduce circulating concentrations of postprandial triacylglycerol - an established independent risk marker for coronary heart disease (CHD). The exercise-induced reduction in postprandial triacylglycerol concentrations has been shown to coincide with transient changes in other CHD risk markers, including reductions in postprandial insulin, interleukin-6, arterial stiffness and resting arterial blood pressure, and exercise may also promote sleep duration and quality. Individual variability in these responses is suspected but has not been examined using robust designs and appropriate statistical models. A recent approach to quantify individual variability in the intervention response involves quantifying the participant-by-condition interaction from replicated intervention and comparator arms. Using this approach (the replicated crossover design), the present study will (i) examine whether the postprandial CHD risk marker and sleep responses to acute exercise are reproducible on repeated occasions; and (ii) determine whether there is true individual variability in postprandial CHD risk marker and sleep responses to acute exercise.

A total of 20 healthy, recreationally active men will be recruited. Participants will undertake a preliminary measures visit (visit 1) to confirm eligibility, to undergo anthropometric measurements and to determine maximum oxygen uptake. Participants will complete four, 2-day experimental conditions in randomised sequences separated by at least one week: two identical control and two identical exercise conditions. On day 1 (visits 2, 4, 6 and 8), participants will arrive fasted at 08:00 and a baseline blood sample, blood pressure and arterial stiffness measurement will be taken. Participants will consume a standardised high fat breakfast at 08:45 (0 h) and lunch at 12:45 (4 h). A second arterial stiffness measurement will be taken at 16:45 (8 h). The two control and two exercise conditions will be identical, except that participants will be asked to exercise on the treadmill for 60 minutes at 60% of their maximum oxygen uptake at 15:15 (6.5 h) in both exercise conditions. On day 2 (visits 3, 5, 7 and 9), participants will arrive fasted at 08:00 and will rest in the laboratory throughout the day in the two control and two exercise conditions. Participants will consume a standardised breakfast at 08:45 (0 h) and a standardised lunch at 12:45 (4 h). Venous blood samples will be collected at 0, 0.5, 1, 2, 3, 4, 4.5, 5, 6, 7 and 8 h. Resting arterial blood pressure will be measured at hourly intervals. Arterial stiffness will be measured at 0, 2.5 and 5 h. Sleep duration and quality will be assessed for three nights before and two nights after visits 3, 5, 7 and 9 using a triaxial actigraphy watch.

Reproducibility and individual variability will be explored by correlating the two sets of response differences between exercise and control conditions. Within-participant covariate-adjusted linear mixed models will be used to quantify participant-by-condition interactions. It is hypothesised that (i) control-adjusted postprandial CHD risk marker and sleep responses to acute exercise will be reproducible; and (ii) true interindividual variability will exist in postprandial CHD risk marker and sleep responses to acute exercise beyond any random within-subject variation.