Hourly 4-s Sprints Prevent Impairment of Postprandial Fat Metabolism from Inactivity

High postprandial plasma lipids (PPL; i.e., triglycerides) are a risk factor for cardiovascular disease. Physical inactivity, characterized by prolonged sitting and a low step count, elevates PPL and thus risk of disease.

This study determined if the interruption of prolonged sitting (i.e., 8 h of inactivity) with hourly cycling sprints of only 4-s duration each (i.e., 4 s × 5 per hour × 8 h = 160 s·d SPRINTS) improves PPL. The 4-s sprints used an inertial load ergometer and were followed by 45 s of seated rest.

Four men and four women participated in two trials. Interventions consisted of an 8-h period of sitting (SIT), or a trial with equal sitting time interrupted with five SPRINTS every hour. The morning after the interventions, PPL and fat oxidation were measured over a 6-h period. Plasma glucose, insulin, and triglyceride concentrations were measured bihourly and incremental area under the curve (AUC) was calculated.

No differences (P > 0.05) between interventions were found for plasma insulin or glucose AUC. However, SPRINTS displayed a 31% (408 ± 119 vs 593 ± 88 mg·dL per 6 h; P = 0.009) decrease in plasma triglyceride incremental AUC and a 43% increase in whole-body fat oxidation (P = 0.001) when compared with SIT.

These data indicate that hourly very short bouts (4 s) of maximal intensity cycle sprints interrupting prolonged sitting can significantly lower the next day's postprandial plasma triglyceride response and increase fat oxidation after a high-fat meal in healthy young adults. Given that these improvements were elicited from only 160 s of nonfatiguing exercise per day, it raises the question as to what is the least amount of exercise that can acutely improve fat metabolism and other aspects of health.