In a study of 17,000 Harvard alumni, reported late in 1977, those who exercised vigorously and steadily over a 10-year period suffered 64 percent fewer heart attacks than their inactive counter-parts.

These findings are backed up by previous studies conducted by the California Population Laboratory and Longevity Research Institute which indicated the influence of strenuous exercise and moderate eating habits in reducing the changes of vascular and other degenerative diseases.

It is clear that exercise is desirable. There is a myth, probably invented in a hammock on a lazy summer afternoon, that exercise utilizes few calories and is therefore not worth considering as a means of weight control.

Don't believe it. Standing up beside that hammock takes a few more calories than lying in it. Walking away from it takes more. If you keep on walking at a brisk rate for an hour you will burn off 300 to 400 calories. If you did that each day, in a week you would have accounted for 2,100 to 2,800 calories, without cutting your food intake by a single one.

The list included here shows the caloric expenditure per hour entailed in various activities.

Canoeing -- 2.5 mph (180); 4 mph (420)

Climbing -- (700-900)

Cycling -- 5 mph (250); 10 mph (450); 14 mph (700)

Dancing -- (200-400)

Horseback riding -- walking (150); trotting (500); galloping (600)

Golfing -- (300)

Gymnastics -- (200-500)

Playing tennis -- (400-500)

Playing soccer -- (550)

Playing squash -- (600-700)

Rowing -- peak effort (1,200)

Running -- (800-1,000)

Sawing wood -- (400-600)

Sculling -- 20 strokes per min. (420); 37 strokes per min. (670)

Sitting at rest -- 15

Skiing -- (600-700)

Standing relaxed -- 20

Swimming -- breast and back strokes (300-650); crawl (700-900)

Walking -- slowly 2.5 mph (115); moderately 3.75 mph (215) very fast 5.5 mph (565)

Writing -- (20)

Three types of activity have been found to play beneficial roles in controling heart disease:

1. Moderate daily physical activity, such as brisk walking for an hour or so. People whose jobs keep them moving around have significantly lower mortality from coronary disease than those whose occupation keeps them sitting all day.

2. Vigorous exercise at least three or four times a week for at least 20 minutes each time -- something that gets the pulse racing to about 110 beats a minute. Squash, a hard game of tennis and swimming are examples. But don't begin this kind of exercise without first getting the green light from your doctor; that is, passing a thorough physical, including treadmill and EKG tests.

3. Sustained hard physical labor, the sort you would get if you felled trees by hand, tilled the field with oxen and plow, or lived where all travel was on foot. Since this is hardly likely for us sedentary urban dwellers, we must count on a low-calorie, low-cholesterol, low-saturated-fat diet, along with exercise and weight control.

Stay healthy!