The unique aspects of the new recommendation on physical health is distinct in two important ways. First, the health benefits of moderate-intensity physical activity are emphasized. Second, accumulation of physical activity in intermittent, short bouts is considered an appropriate approach to achieving the activity goal.
The new recommendation extends the traditional exercise-fitness model to a broader physical activity-health paradigm.
|Fitness for health|
The unique elements of the recommendation are based on mounting evidence indicating that the health benefits of physical activity are linked principally to the total amount of physical activity performed.
The evidence suggests that amount of activity is more important than the specific manner in which the activity is performed (ie, mode, intensity, or duration of the activity bouts).
The health benefits of physical activity appear to accrue in approximate proportion to the total amount of activity performed, measured as either caloric expenditure or minutes of physical activity. For example, observational studies have shown a significantly lower death rate from CHD in people who perform an average of 47 minutes vs 15 minutes of activity per day, and in men who expend an estimated 2000 or more calories per week vs those who expend 500 or fewer calories per week.
There is a clear association between total daily or weekly caloric expenditure and cardiovascular disease mortality.
In most of the epidemiologic studies that have demonstrated this association, physical activity was assessed by questionnaires, and total activity was summed during periods ranging from 1 day to 1 year and then reported as average daily or weekly levels of physical activity.
For example, among Harvard alumni the summed activity consisted of blocks walked, flights of stairs climbed, and moderate and vigorous sports play. In the Multiple Risk Factor Intervention Trial, the most frequently reported activities were lawn and garden work (80% of men), walking (65%), and home repairs (60%).
It is not possible to ascertain with certainty whether the activity reported in these studies was performed in single, continuous daily bouts or was accumulated in multiple episodes. However, the nature of the most frequently reported activities suggests that it is unlikely that most of the activity was performed continuously. It is more likely that the daily or weekly caloric expenditures reflect accumulation of activity, most of which was performed intermittently. Also, the activities most commonly reported in these studies (eg, walking, lawn work, and gardening) typically are performed at moderate intensity.
Two published experimental studies have addressed the effects of continuous vs intermittent activity on fitness. DeBusk examined the effects of three 10-minute bouts of moderate to vigorous activity daily compared with a single 30-minute daily period of exercise of equal intensity in men.
Ebisu studied the effects of running on fitness and blood lipids in three groups of men. Subjects were divided into three exercise groups and one inactive control group. Each exercise group ran the same total distance, but in one, two, or three sessions daily. In both studies, fitness (measured as maximal oxygen uptake) increased significantly in all exercise groups, and the differences in fitness across the exercising groups were not significant. In the latter study, high-density lipoprotein (good) cholesterol levels increased significantly only in the group that exercised three times per day.
Although more research is needed to better elucidate the health effects of moderate- vs high-intensity activity and intermittent vs continuous activity, clinicians and public health practitioners must rely on the most reasonable interpretation of existing data to guide their actions.
We believe that the most reasonable interpretation of the currently available data is that caloric expenditure and total time of physical activity are associated with reduced cardiovascular disease incidence and mortality; there is a dose-response relationship for this association; regular moderate physical activity provides substantial health benefits; and intermittent bouts of physical activity, as short as 8 to 10 minutes, totaling 30 minutes or more on most days provide beneficial health and fitness effects.
Clinical experience and limited studies suggest that people who maintain or improve their strength and flexibility may be better able to perform daily activities, may be less likely to develop back pain, and may be better able to avoid disability, especially as they advance into older age. Regular physical activity also may contribute to better balance, coordination, and agility, which in turn may help prevent falls in the elderly.
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