It’s official. Obesity rates are on the rise in most western countries where sitting at a computer all day (and sometimes into the night) is commonplace. Low activity levels, in many cases, combined with poor diets, have been blamed for almost two-thirds of Americans being overweight or obese. To help address the problem, health researchers have developed an iPhone app designed to monitor your physical activity and motivate you to do that little bit more.

Chinmay Manohar, from the Department Endocrinology, Nutrition and Diabetes of the Mayo Clinic, and his team have developed a program that helps people monitor their normal daily physical activity using a cell phone or mp3 player.

Manohar’s department learned that leaner people tended to spend two and a half more hours per day standing than did heavier people, indicating that leaner people were more active even when they weren't exercising. "If that is the case, why don't we encourage people to get out of their chairs?" said Manohar.

The team settled on the iPhone and the iPod Touch because of the accessibility and popularity, and the fact that they have built-in motion sensors (accelerometers).

They created a program called Walk n'Play that can be downloaded for free through iTunes, and as more smart phones adopt the motion sensor technology, the likelihood of the program becoming compatible between platforms will not be difficult, says Manohar.

The current version of Walk n’Play is quite simplistic. Users input their height and weight into the program and throughout the day, their score can be monitored. The program updates the users with information, telling them if they are winning or losing against the computer. Manohar says there is no pressure nor specific exercises to undertake. But he believes turning physical activity into a game makes people more competitive and more likely to get active.

Manohar feels most off-the-shelf devices are unreliable for measuring the lower speeds detected by the Walk n'Play because they are used for measuring exercise like jogging or running, not for the day-to-day movement for which the Walk n'Play is designed. The program was tested on 31 volunteers for the ability to detect changes in movement as little as 0.5mph. Movements like sitting, standing and lying down and seven speeds on the treadmill were tested to determine how precise the program was. Using the results of these movement tests, Manohar's group developed a gold standard for typical movements used in daily activities.

So far, more than 10,000 people have downloaded the Walk n'Play, but Manohar knows it will take more than a basic activity monitor to keep people's interest.

"You have to put an element of fun into the whole thing to encourage people to be more active," Manohar said, "we put people into a gaming mind-set and people unknowingly do exercise and have fun doing it."

The group has included a “buddy” function into the program by integrating basic social networking capabilities. Manohar says fitness and weight-loss is easier to do with a buddy. The newer features will allow a person to play against their friends or even compete with people or top performers from other countries or time zones. Users can even post their performance as their Twitter status.

According to Manohar, most people know they need more exercise to maintain a healthy weight but lack the motivation. He hopes using programs like the Walk n'Play will encourage people to make incremental changes in their daily activities that will lead to better health.

Manohar is currently presenting his team's work at the 2010 Experimental Biology meeting in Anaheim, California, on April 24-28.