Trial Information

BACKGROUND:

Current government physical fitness guidelines state that: 1) the majority of the health
benefits from physical activity can be obtained by walking two miles briskly on most days of
the week; and 2) the health benefits of physical activity depend principally on the total
amount of activity rather than the intensity of the activity. Nevertheless, there are
currently no prospective epidemiological studies extant, designed specifically to directly
contrast the health benefits and costs of moderate exercise (e.g., walking) versus vigorous
exercise (e.g., running).

DESIGN NARRATIVE:

Before the start of the study, 233,000 person-years of follow-up had been accumulated in
56,000 runners (between 1991 and 1997). The runners were resurveyed in 1997 along with
68,000 walkers. The walkers were also solicited through the publication of the questionnaire
in Walking magazine followed by a direct mailing of the questionnaire to 425,000
subscribers. Total and cause-specific mortality will be determined from the National Death
Index; fatal and nonfatal cancers will be identified from the National Cancer Institute's
Surveillance, Epidemiology, and End Results (SEER) and 46 state registries; nonfatal
coronary heart disease and injuries will be determined from questionnaires. Survival
analyses will be used to test whether runners have greater reduction in heart disease, total
mortality, and cancer per unit of exercise. Exercise-related injuries from walking and
running will also be examined. Power calculations suggest that detection of differences
between runners and walkers, as small as 11% for total mortality, 16% for CHD, 12% for total
cancers, and 36% for breast cancer, will be possible. The differences will be adjusted for
weekly kilocalories expended by walking and running, for walking and running distance, and
for time spent on each activity to test whether these variables account for differences in
disease rates between walkers and runners.

By the end of the study, 517,000 person years in 68,000 runners (between 1991 and 2001) will
be available for analysis. Survival analysis will be used to test for a dose-response
relationship between running mileage and CHD and cancer risk, and whether this relationship
is affected by running intensity, running frequency, running history, gender, adiposity, age
or medication use. Using conservative rates (25% below published values), statistical power
calculations suggest that detectable reduction in coronary heart disease risk as small as
0.71% per mile will be possible, which is far below the estimated reduction from other
published studies (2.1%). Additionally, a detectable reduction in breast cancer risk as
small as 1.5% per mile run in women is calculated, which is below the 1.7% reduction in risk
estimated from other published data.