Effects of high-intensity intermittent exercise on fat loss, cardiovascular, and autonomic function

Abstract

This thesis consists of a series of publications that address public health questions in the field of exercise physiology. The thesis aimed to investigate the effects of high-intensity intermittent exercise (HIIE) on fat metabolism, fat loss, and cardiovascular and autonomic function and is composed of two studies. Study I used a comparative research design to compare the metabolic response to acute HIIE of trained and untrained young males. Males completed 20 min of HIIE consisting of 8-sec fast pedalling at 65% of maximum workload followed by 12-sec of slow pedalling at 25% of maximum workload. Blood lipids, glucose, lactate, and catecholamine response of two groups was compared. Study II used a randomised controlled trial to examine the effects of 12 weeks of HIIE training on abdominal, visceral, total body fat mass, and fat free mass of young males. Cardiovascular and autonomic response to HIIE at rest and during mental and physical challenge was also investigated. Males completed 20 min of interval sprinting, 3 times per week, for 12 weeks. Study I found that trained compared to untrained males recorded similar response to acute HIIE. Fat oxidation rate increased significantly in both groups after acute exercise with no difference between groups. Glycerol level was significantly elevated for both groups during exercise. Lactate concentration also increased in both groups during HIIE, however, was higher for untrained males. Furthermore, both groups showed significant increases in epinephrine and norepinephrine during HIIE. In Study II aerobic fitness improved for the exercise group who, compared to controls, showed greater total fat, abdominal, trunk, and visceral adiposity fat loss and greater increase in fat free mass. The exercise group also recorded a significant reduction in heart rate accompanied by increased stroke volume at rest and during mental and physical challenge. Forearm vasodilatory capacity and forearm blood flow of the exercise group increased during the first two min of Stroop although remained unchanged at rest. Also, arterial stiffness, heart period variability and baroreflex sensitivity increased significantly at rest and during Stroop. It is concluded that acute HIIE training generated similar metabolic responses for both trained and untrained males. Twelve weeks of chronic HIIE had positive effects on body composition, and cardiovascular and autonomic function of overweight males at rest and during mental and physical challenge.