<p>The energy required for the performance of light exercise is largely supplied by the aerobic oxidation of fat and carbohydrate. As the intensity of exercise increases, the percentage of energy derived from anaerobic processes, predominantly the breakdown of muscle glycogen to lactic acid, is increased proportionally. Evidence suggests that the increase in anaerobic metabolism influences the mobilization of free fatty acids from adipose tissue. Studies have shown that lactate inhibits FFA mobilizltion in dogs. In man, it was found that plasma FFA are reduced during heavy exercise and remain low as long as plasma lactate is increased. However, when lactate is increased under these conditions, the pH is reduced.</p> <p>To separate the effects of pH and lactate in the blood, subjects performed three identical exercise tests with artificially induced changes in blood pH prior to two of the studies. Ammonium chloride and sodium bicarbonate were ingested over a three hour period prior to exercising to produce an acidosis and alkalosis, respectively. Calcium carbonate was given as a placebo for the control study. In all subjects, the studies were performed in a random order, in a fasted state and were separated by at least 72 hours. Arterialized venous blood was sampled from a vein in the hand.</p> <p>The maximum power output of each subject was measured by a progressive exercise test to exhaustion on a cycle ergometer. During the studies, they exercised at 33% and 66% of their maximum power output for 20 minutes each, followed by 90% until exhaustion.</p> <p>This protocol resulted in a significant separation in both blood pH and exhaustion times at the 90% workload. The mean exhaustion times were 4 min., 2.5 min., and 6.5 min. for the control, acidosis and alkalosis studies, respectively.</p> <p>The plasma lactate concentrations were also significantly different. The lowest lactate levels were found during acidosis and the highest during alkalosis.</p> <p>Plasma glycerol and FFA concentrations were similar during the control and alkalosis studies, but significantly lower during acidosis. The lowest levels of glycerol and FFA were found when the pH was lowest, but plasma lactate was also lowest.</p> <p>These results suggest that changes in pH are more important than changes in lactate, per se, in the inhibition of FFA mobilization during severe exercise. In addition, it appears that acidosis causes either a decreased rate of production of lactic acid, a decreased rate of efflux of lactate from muscle, or an increased utilization of lactate by other tissues.</p> <p>Although the mechanisms cannot be determined from this study, the results suggest that acidosis inhibits glycolysis as well as FFA mobilization, reducing the anaerobic production of energy. This presents no serious problem during moderate exercise, but seriously impairs performance of heavy work.</p> / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/7246 |
| Date | 10 1900 |
| Creators | Taylor, Robert |
| Contributors | Jones, N.L., Medical Sciences |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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