The short-term effects of physical inactivity and diet on cardiovascular and metabolic responses in healthy humans

Abstract

Introduction: reduced physical activity is a major predisposing factor for the development of cardiovascular and metabolic disorders. Current lifestyle changes, such as increased intake of high-calorie foods in combination with physical inactivity are considered to play an important role in cardiometabolic disorders worldwide.

Aims: the overall aim of this thesis was to examine the short-term effects of physical inactivity and energy balance on cardiometabolic responses in healthy humans. Two studies were performed under free-living and standardised laboratory conditions. Study 1 (Chapter 3) aimed to assess the effects of a 2-day reduced physical activity with and without a proportional decrease in energy intake (creating neutral or positive energy balance, respectively), on cardiovascular responses, insulin sensitivity and energy metabolism in eight healthy men and women. Study 2 (Chapter 4) aimed to examine brachial artery endothelial function using the flow-mediated vasodilatation (FMD) technique before and after a 5-day reduced physical activity with a proportional decrease in energy intake to create a neutral energy balance in eight healthy men.

Methods: cardiovascular responses were measured using the Finometer and venous occlusion plethysmography. Insulin sensitivity was evaluated using the Matsuda index and the Homeostatic Model Assessment for Insulin Resistance. Energy metabolism was assessed by indirect calorimetry. FMD responses were measured using the Duplex-Doppler Ultrasound. The continuous glucose monitoring system, FreeStyle Libre Abbott, performance was compared against the Medtronic iPro2 and arterialised blood glucose measurements using the yellow spring instrument (YSI). Results: reduced physical activity with positive energy intake was associated with an increase in 24-hour glucose concentrations (p = .035 with large effect of η2 p = 0.38), an increase in postprandial heart rate (p < .001 with large effect size of η2 p = 0.19) and an increase in insulin incremental area under the curve (p = .051 with large effect η2 p = 0.35) in response to a mixed meal. These changes improved when energy intake was reduced to match energy expenditure (Study 1). No significant changes in brachial FMD response were detected following short-term inactivity (Study 2). Glucose measurements by the FreeStyle Libre Abbott tended to be lower compared to the Medtronic iPro2 (p < .001 with large effect of η2 p = 0.33) but has a good agreement with the arterialised blood glucose measurements (Abbott vs YSI MARD 12.69% and iPro2 vs YSI MARD 16.15%).

Conclusions: physical inactivity with energy surplus is associated with unfavourable cardiovascular and metabolic changes. As a secondary objective, the FreeStyle Libre Abbott is potentially a useful tool to assess the daily glucose profile in healthy normo-glycaemic individuals.