Evolution of physical activity guidelines reflects changing body
of evidence Scientific knowledge about physical activity and
health is of little value if people cannot understand it and
apply it to their lives. For the past three decades, there has
been a gradual but steady development in the effort to present
information on physical activity and health to the general
public. Research has repeatedly shown that exposure to regular,
frequent bouts of physical activity stimulates physiological and
metabolic changes that benefit health. It is helpful to classify
these as either (a) chronic effects, that is, adaptations to
training acquired over weeks or months, or (b) short-term, acute
responses to each individual session of activity. While
psychological, social, and environmental factors contribute
significantly to physical activity behavior, it is important to
recognize that activity behavior also has a biological basis and
that genetic variation could affect individuals’ propensity to
be physically active or