Results: The highest amount of weekly exercise, with minimal weight change, had modest beneficial effects on blood lipoprotein profile. The improvements were related to the amount of activity and not to the intensity of exercise or improvement in fitness. Both lower amount exercise groups always had better responses than the control group.
Exercise training had no significant effect on the total cholesterol or LDL cholesterol concentrations. It did, however, exert effects on the concentrations of LDL cholesterol subfractions, but the clinical importance of this change is unclear. HDL cholesterol increased a modest 9% in the high amount high-intensity group; a change from baseline of 42.1 mg/dl to 45.9 mg/dl (9% change). There were no appreciable changes in HDL cholesterol in the other exercise groups.
Blood triglyceride levels showed a reduction in all exer¬cise groups, as to be expected. Triglyceride concentrations are sensitive to weight loss and exercise, but as emphasized above triglyceride levels bear a low relationship to athero-matous coronary artery disease or vascular disease in general.
B. Other Effects
Vigorous exercise causes a variable effect on blood-clotting factors. A substance in the blood, factor VIII, is necessary for blood clotting and is absent in bleeders (hemophiliacs). Hemophiliacs who exercise get a mild and helpful increase in factor VIII. Vigorous exercise in healthy individuals increases factor VIII, as well as the number and stickiness of platelets. This is offset in healthy young individuals by a mild increase in factors that tend to dissolve blood clots. Individuals who have atherosclerosis of the artery present have an impaired ability to dissolve clots. Consequently, small clots (thrombi) may form on plaques of atheroma, thus increasing their size. Slowly, over 5–10 years, this may cause or promote existing coronary heart disease. Rapid walking at a rate of four miles per hour, however, does not cause an increase in factor VIII or platelets, and the stickiness of platelets is slightly reduced. Therefore, walking two to three miles daily remains the best exercise.

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