Physical inactivity greatly increases the risk of heart attack, stroke, metabolic syndrome,
and other cardiovascular diseases. The CDC estimates that being sedentary
increases the risk of coronary heart disease by 1.5 to 2.4 times. Exercise
training improves many metabolic factors that are associated with reduced risk of
cardiovascular disease including lower blood pressure, increased high-density lipoprotein cholesterol (HDL-C), reduced serum triglyceride, lower LDL-Cholesterol
levels, and possibly, increased numbers of larger safer LDL-C molecules and decreased
numbers of small more dangerous LDL-C molecules.

The Council on Clinical Cardiology and the Council on Nutrition, Physical Activity,
and Metabolism have concluded that both epidemiological studies of occupational
and leisure-time physical activity, and objective measures of exercise capacity such
as treadmill performance, have consistently documented a causal relationship between
physical activity and a reduced incidence of coronary artery disease (CAD)
events. Studies find that the most physically active subjects generally have CAD
rates half of those of the most sedentary group.

Independent of the volume of activity, engaging in some vigorous activity is more
beneficial to health than moderate physical activity—higher-intensity activities provide
more cardioprotection. One investigator has suggested that two minutes
of moderate physical activity may not be equivalent to one minute of vigorous activity,
and that running beats walking by a factor of between 2:1 to 4:1 in mortality
reduction at the same volume of physical activity as measured by metabolic equivalents.

A meta-analysis to evaluate the association between cardiorespiratory fitness and
coronary heart disease or all-cause mortality, evaluated data from 33 eligible studies.
Over a follow up of 1.1 to 26 years, study participants with low cardiorespiratory
fitness were found to have had a 70% higher risk for all-cause mortality
and a 56% higher risk for coronary heart disease/cardiovascular events than study
participants with high cardiorespiratory fitness.

A study of more than 30,000 Australian women born in the 1920s, 1940s, and 1970s
in the British Journal of Sports Medicine found that physical activity reduced the
risk of heart attack, stroke, metabolic syndrome and other cardiovascular diseases.
It considered physical inactivity, excess weight, smoking, and high blood
pressure. Among the four factors studied, up to age 30, smoking was the most
important contributor to heart disease. From age 30 until the late 80s, low physical
activity levels were responsible for higher levels of risk than any of the three other
risk factors. The potentially important role of nutrition and blood cholesterol levels
was not evaluated in the study.