Chronic effects of high intensity interval training on postprandial lipaemia in healthy individuals

BACKGROUND: Dyslipidaemia is associated with atherosclerosis and subsequent cardiovascular disease. Acute high intensity interval exercise (HIIT) is a time-efficient means to improve postprandial lipaemia (PPL), but little is known about its cumulative effects. AIM: To investigate the chronic effects of HIIT on PPL and metabolic health in healthy young individuals. METHODS: Following ethical approval, 8 recreationally active males (mean ± SD: 22 ± 3years, 1.77 ± 0.07m, 67.7 ± 6.2kg) undertook two 6h mixed-meal tolerance tests, before the first session and ≥72h after the final session of four weeks of HIIT (16 sessions; 10x60s bouts of cycling at 90%VO2max, interspersed by 60s intervals at 45%VO2max). A vastus lateralis muscle sample was taken in the fasted state before and after training. Regular arterialised and deep venous blood samples across the forearm, brachial artery blood flow measurements, and whole body indirect calorimetry data were obtained before, and at regular intervals for 6h after consumption of the mixed-meal tolerance test before and after training. RESULTS: VO2max (mean ± SEM) increased from 47.30 ± 5.46 to 51.80 ± 3.41mLO2∙kg-1∙min-1 (P < 0.01), without changes in body mass. Neither fasting circulating triglyceride (TAG) concentrations and postprandial responses, nor skeletal muscle protein content of lipolytic enzymes were altered with training. Free fatty acid (FFA) forearm uptake and fractional extraction significantly increased after training (ANOVA main effects; P = 0.03 and P = 0.048, respectively), with a strong trend towards increased blood flow in the latter half of the tolerance test (P = 0.07). CONCLUSIONS: Four weeks of HIIT increases cardiovascular fitness and the postprandial uptake and extraction of FFA across the forearm but has no chronic effect on circulating TAG. Our findings suggest the frequently observed exercise-induced reduction in postprandial TAG is a transient effect of the last exercise bout, and highlight the importance of regular exercise for the maintenance of training-induced benefits to postprandial lipaemia