Mixed
Vigorous aerobic exercise performed habitually reduces the incidence of coronary heart disease and total mortality, but only if the exercise exceeds a specific intensity threshold (e.g., >6 METs or >65% max oxygen uptake); non-vigorous high-volume physical activity provides no such protection.
To protect your heart, you must exercise vigorously enough to significantly raise your heart rate and breathing (e.g., fast walking >4mph, vigorous sports, or cycling) on a regular, habitual basis. Simply being 'active' or burning many calories through low-intensity tasks (like gardening or light walking) will not reduce your risk of coronary heart disease. The protection is specific to the intensity and the continuity of the effort.
The 9% of men who reported that they often participated in vigorous sports or did considerable amounts of cycling or rated the pace of their regular walking as fast (over 4 mph, 6-4 kmlh) experienced less than half the non-fatal and fatal coronary heart disease of the other men... When these forms of exercise were not vigorous they were no protection against the disease, nor were other forms of exercise or high totals of physical activity per se.
Why this rating
Prospective cohort study with long follow-up (9+ years) and rigorous case-cohort design, though observational and subject to self-selection bias.
Source
Exercise in leisure time: coronary attack and death rates.
J.N. Morris et al. · Heart · 1990
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →