Abstract MP026: Does the Replacement of Moderate-Intensity with Vigorous-Intensity Physical Activity Further Reduce All-Cause and Cardiovascular Mortality?

Abstract

The 2008 US federal guidelines require a minimum of 150 minutes/week of moderate-intensity, or 75 minutes/week of vigorous-intensity physical activity, or an equivalent combination of the two, for health benefits. Thus, they assume a 2:1 equivalence between the two intensities of activity; i.e., 2 minutes of moderate-intensity activity is equivalent to 1 minute of vigorous-intensity activity. However, no studies have specifically examined whether this assumption is correct. Purpose: To examine the effect of replacing 150 minutes/week of moderate-intensity with 75 minutes/week of vigorous-intensity physical activity on all-cause and cardiovascular disease (CVD) mortality. Methods: 8,859 men (mean age, 66.4 yr) from the Harvard Alumni Health Study, free from CVD and cancer, were followed from 1988 to 2008. At baseline (1988) and in 1993, men reported physical activity (blocks walked, stairs climbed, and a listing of sports/recreational activities and participation time). Time spent per week in sports/recreational activities of moderate-intensity (3 to <6 METs, or multiples of resting metabolic rate) was summed and expressed as units (or fraction of units) of 150 minutes/week. Similarly, time spent in vigorous-intensity (≥6 METs) sports/recreational activities was summed, expressed as units (or fraction of units) of 75 min/week. Total and cause-specific mortality was identified from the National Death Index. Cox proportional hazards models calculated the risks of all-cause and CVD mortality, examining the effect of replacing 150 minutes/week of moderate-intensity with 75 minutes/week of vigorous-intensity physical activity, controlling for the total amount of physical activity. Results: During follow-up, 4,064 men died, including 1,192 from CVD. In multivariate analyses, controlling for the total physical activity, age, smoking, intakes of alcohol, vegetable, fruit, and saturated fat, and total caloric intake, replacing 150 minutes/week of moderate-intensity with 75 minutes/week of vigorous-intensity physical activity was associated with an additional 2% reduction in all-cause mortality (Hazard Ratio (95% confidence interval) = 0.98 (0.96, 1.00); p = 0.05), and an additional 5% reduction in CVD mortality (0.95 (0.92, 0.99); p = 0.02). Conclusions: The assumption that 2 minutes of moderate-intensity activity is equivalent to 1 minute of vigorous-intensity activity under current federal guidelines is not strictly correct. Vigorous-intensity physical activity is associated with additional risk reduction for CVD mortality compared to moderate-intensity physical activity. Although there is an added, statistically significant benefit of vigorous-intensity over moderate-intensity physical activity, the magnitude of benefit is small.