How much and what type of physical activity is enough? What doctors should tell their patients.

Summarized by Robert W. Griffith, MD
December 5, 2005

Introduction

There's no doubt that physical fitness improves cardiovascular fitness, and reduces the chances of an early cardiovascular death. But just how much exercise is necessary to get that protection? And what sort of exercise should one do? In other words, what are the ideal frequency, intensity, and duration of workouts? An editorial in theArchives of Internal Medicine reviews the problem, based on a recent study sponsored by the American College of Sports Medicine¹. Here's a summary of what it had to say.

The study design

Participants in the study were allocated to physician-assisted counseling, or to one of 4 programs composed of 2 exercise intensities and 2 exercise frequencies. The intensity was based on % of maximum heart rate (HR) and the frequency on number of sessions per week - 3-4 (low) or 5-7 (high). Thus there were 4 programs:

• Moderate intensity, low frequency
• Moderate intensity, high frequency
• High intensity, low frequency
• High intensity, high frequency

The exercise chosen was walking, and the duration was kept the same for all 4 groups - 30 minutes. Cardiorespiratory fitness was the main measure (maximum oxygen uptake), along with assessment of cardiac risk factors after 6 and 24 months.

The results

Moderate intensity exercise (at either low or high frequency), low intensity, high frequency exercise, and moderate intensity, low frequency exercise all produced significant increases in cardiorespiratory fitness at 6 months; however, only the high intensity, high frequency exercise improved the cholesterol levels significantly. After 24 months, similar results were obtained, but the benefit on the cholesterol levels was lost.

Current thinking

The usual recommendation doctors should give their patients is to do moderate intensity exercise for 30 minutes 5 days a week, or more vigorous exercise for 20 minutes 3 days a week. Moderate intensity means 3-6 metabolic equivalents, or METS.

Practical considerations

Obviously, new exercisers should be advised to start slowly, and increase up to the recommended intensity/frequency/duration. In the study there was no significant difference in adherence to the program between high and low frequency participants, so recommending 5-7 days a week is not a deterrent. And there was a fall-off in adherence by the high intensity vs. the low intensity participants, so moderate exercise 5-7 days a week seems the best solution, if it's practical for the individual.

In a separate study, nearly all (97%) of a group of older men and women describing themselves as 'walking briskly' had an observed walking speed of equivalent to 3 or more METs, based on their calculated walking speed, 3 mph (=4.83 km/h).

Conclusions

The study reviewed confirms the benefits of moderate-intensity walking (or an equivalent aerobic workout) on cardiorespiratory fitness. And one should not neglect some of the other benefits of moderate physical activity - a lowered risk of developing the metabolic syndrome, type 2 diabetes, overweight problems, and so on.

Source

• Estimated risks for developing obesity in the Framingham Heart Study. BSN. Blair , Arch Intern Med, 2005, vol. 165, pp. 2324--2325

Footnotes
1. Prescribing exercise at various levels of intensity and frequency. DGE. Duncan , ASD. Anton , SSJ. Sydeman ,  et al., Arch Intern Med, 2005, vol. 165, pp. 2362--2369

Related Links
Are You a Weekend Warrior?
Start Getting Fit When You're Young - Here's Why!
Exercise, and Energy Expenditure

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.