A single bout of strenuous endurance exercise reduces fasting plasma triglyceride (TG) concentrations the next day (12-24 h later) by augmenting the efficiency of very low-density lipoprotein (VLDL)-TG removal from the circulation. Although much of the hypotriglyceridemia associated with training is attributed to the last bout of exercise, the relevant changes in VLDL-TG metabolism have never been investigated. We therefore examined basal VLDL-TG kinetics in a group of sedentary young men (n=7), who underwent two months of supervised high-intensity interval training (3 sessions/wk; running at 60% and 90% of peak oxygen consumption in 4-min intervals for a total of 32 min; gross energy expenditure: 446±29 kcal), and a non-exercising control group (n=8). Each subject completed two stable isotope labeled tracer infusion studies in the post-absorptive state, once before and again after the intervention (~48 h after the last exercise bout in the training group). Peak oxygen consumption increased by ~18% after training (P0.05), whereas body weight and body composition were not altered. Fasting plasma VLDL-TG concentration was reduced after training by ~28% (P0.05), and this was due to reduced hepatic VLDL-TG secretion rate (by ~35%, P0.05) with no changes (<5%, P>0.7) in VLDL-TG plasma clearance rate and the mean residence time of VLDL-TG in the circulation. No significant changes in VLDL-TG concentration and kinetics were observed in the non-exercising control group (all P0.3). We conclude that a short period of high-intensity interval aerobic training lowers the rate of VLDL-TG secretion by the liver in previously sedentary men. This is different from the mechanism underlying the hypotriglyceridemia of acute exercise; however, it remains to be established whether our finding reflects an effect of the longer time lapse from the last exercise bout, an effect specific to the type of exercise performed, or an effect of aerobic training itself.