By BRIAN LEVINE, MD

When it comes to discussing exercise with friends, family and patients, it seems that many of us are at a loss for words. What kind of exercise should we recommend? How much exercise is enough? How much is too much? How do I know that my patient is actually exercising? How do I prescribe exercise?

According to the U.S. Department of Health and Human Services, U.S. adults should engage in moderately intense physical activity for a minimum of 150 minutes each week; this is equivalent to 30 minutes a day, 5 days per week [1]. While it is relatively easy to keep track of the duration and frequency of exercise, it is much more difficult to quantify the intensity of an activity, let alone ensure that the activity is “moderate” for the entire 30 minutes.

In fact, in a 2008 study of women’s understanding of “moderate-intensity” of physical activity as presented in the popular media, the authors found it is not enough to simply hear and read a description of physical activity, but that it requires practice [2].

So, what are we to do? Should we have our patients log their daily activities? Should we have our patients show us sign-in sheets from the local gym?

It turns out that the dilemma of how to quantify physical activity has been a hot topic for more than 50 years. In 1965, a Japanese inventor developed the first pedometer to give people the opportunity to meet measurable goals and, thus, increase their physical activity. The device was called the Manpo-Kei (meaning “10,000 steps meter”) and it was based on research by Dr. Yoshiro Hatano that demonstrated that 10,000 steps per day allowed for a proper balance between the traditional Japanese caloric intake and the activity-based caloric expenditure of walking approximately five miles per day (the average person’s stride length is approximately 2.5 feet long, therefore 2,000 steps/mile) [3].

The validity of the 10,000 step model for Americans has been questioned by many researchers, given that the American diet is far more calorie rich than the 1965 Japanese diet and that five miles of walking per day may be too much for the average individual. A 2008 study that attempted to answer the question, “How many steps/day are enough?” reported that: [4]

• <5,000 steps/day may be used as a ‘sedentary lifestyle index’
• 5,000-7,499 steps/day is typical of daily activity excluding sports/exercise and might be considered ‘low active’
• 7,500-9,999 likely includes some volitional activities (and/or elevated occupational activity demands) and might be considered ‘somewhat active’
• >or=10,000 steps/day indicates the point that should be used to classify individuals as ‘active’
• >12,500 steps/day are likely to be classified as ‘highly active’

This leads us back to the original question of how physicians can effectively prescribe exercise to our patients and then assess their compliance. Well, as you can imagine, there are apps for our smartphones and wireless devices!

Some are free like The Nike+ Running App or RunKeeper; both of these utilize GPS-derived data to track fitness performance. Although the name suggests a running-focus, these applications can be used to monitor all sorts of physical activity like running, walking and cycling. Beyond apps, there are also devices that sync to the internet via a smartphone to monitor your physical activity; popular ones are the FitBit or the Jawbone UP. Lastly, there are even strap-on Bluetooth heart rate monitors such as Pear Sports where the application ultimately “learns” the user’s fitness level and creates custom heart rate zones that ensure that each subsequent workout is at the right intensity.

We as physicians have known for a very long time that diet and exercise are the keys to fitness success. Provided that the sum of the calories burned is greater than the sum of calories consumed, by definition the person should lose weight. But, being able to track, let alone quantify the quality and character of the caloric output is challenging. This is why it is important to recognize that our phones are much more than phones! So, the next time someone asks you about exercise, it may not be unreasonable to prescribe an application.

Brian Levine, MD, M.S. is currently a clinical fellow in reproductive endocrinology and infertility at The Ronald O. Perelman & Claudia Cohen Center for Reproductive Medicine at the Weill Cornell Medical College/New York-Presbyterian Hospital and a fellow of The American Resident Project, where the following post first appeared.