The influence of the intensity of treadmill walking and training status on lipoprotein metabolism in the fasted and postprandial states

The aim of the studies described in this thesis was to investigate the effects of the intensity of treadmill walking and training status on lipoprotein metabolism in the fasted and postprandial states in normolipidaemic individ uals. Twelve young (28±2 years) adults walked on the treadmill on two occasions, for 90 min at low intensity (30% maximal oxygen uptake, V02max) and moderate intensity (60% V02max) after an overnight fast. Venous blood samples were taken during, immediately, 1 and 24 hours after the end of each walk, all in the fasted state. Both exercise bouts reduced the serum triacylglycerol (TAG) concentrations 24 hours after exercise but these decreases were independent of the intensity of the previous exercise bout. In the light of the suggestion that the fasted state may not be a sensitive model to study the TAG metabolic capacity, the above experiment was repeated in young adults (n=12), with the two bouts of treadmill walking taking place 16 hours prior to the ingestion of a high fat meal 0.3 g fat·kg body weight·l , 67% energy from fat). In addition a third trial was introduced in which volunteers did not exercise prior to the ingestion of the meal (control trial). Venous samples were obtained in the fasted state and after the ingestion of the meal at hourly intervals for 6 hours. Moderate, but not low intensity, walking significantly attenuated (26%) the total lipaemic response to the meal compared with the control trial (5.51±0.5 mmoJ.l-l.h vs 7.40±0.7 mmol·J-l·h; p<0.05). However, the moderate intensity bout expended twice the energy expended during low intensity exercise as the two bouts were of similar duration (90 min). The third study, therefore, examined the effect of the intensity of walking on the lipaemic responses to a similar high fat meal in young adults (n=9), when the energy expenditure of the two walking bouts was held constant (90 min at 60% V02max vs 180 min at 30% V02max). In addition, expired air samples were collected before and after the meal in order to examine the metabolic responses to this meal. Both bouts of exercise attenuated to a similar degree (=30%) the total serum TAG response to the meal compared with the non-exercise trial (5.46±0.63 mmol·J-l·h and 5.53±0.58 mmol-l-l.h at low and moderate intensity respectively vs 8.09±1.09 mmol·J-l·h; p<0.05). Mean respiratory exchange ratio over 6 hours after the meal was lower (p<0.05) in both exercise trials than in the control trial indicating an enhanced fat oxidation during the observational period. All the above three studies were conducted in young adults. The aim of the last study was two-fold (i) to examine whether a bout of moderate intensity walking (60% V02max) would influence the lipaemic and metabolic responses to a fat meal in middle-aged women, as already shown for young adults and (ii) to test the hypothesis that this effect would be greater in trained individuals, by comparing these responses between a trained (n=9) and an untrained (n=13) group. Walking attenuated the total postprandial TAG response to the meal compared to the control trial in both trained (4.9±O.3 mmol·j-1·h vs 7.0±O.S mmol·j-1·h; p