Smart phone applications present opportunities for us to keep easier track of our health and fitness, in hopes of making it more likely that we'll reach our goals.

But sorting through all the calorie counters , training schedules and fitness programs can be daunting. MyHealthNewsDaily asked a variety of health and fitness experts for their opinions on what works and what doesn't among the popular apps of 2011.

Here's what they had to say about apps that track your activity or help you train.

Tracking physical activity with iPhones

Accelerometers, a device that allows the phone to track your movements and speed, along with GPS systems built into many devices make them both an easy platform to develop apps that track your steps, your bike route, your yoga schedule and more.

The RunKeeper Pro (free on iPhone and Android) uses GPS to track your runs, while the app measures distance, time, pace, calories burned and heart rate.

AllSport GPS (iOS, Android and BlackBerry) also uses the phone's GPS system to track runs, bikes, walks, in addition to changes in elevation and speed.

Meanwhile, other apps, such as the iMapMy app (Android, iPhone and BlackBerry), lets users link their workouts to social media sites such as Facebook and Twitter, while they track progress via GPS.

While these apps are hugely popular, some fitness experts say they prefer the old-fashioned pedometer, even if it comes in the form of an app such as the All-in Pedometer for the iPhone.

"The extrapolations used by pedometers are typically formulas that have withstood the test of time," said Neal Pire, a fellow with the American College of Sports. "The accuracy and reliability of the technology has been scrutinized, with results replicated many times in peer-reviewed research."

Moreover, Pire said, pedometers have been studied on a "behavioral" basis, meaning that research has shown that the more we use them to track our steps, the more we tend to exercise.

Walter Thompson, a professor at Georgia State University in Atlanta, agreed on the merits of the tried-and-true pedometer.

But accuracy is important, Thompson said. "We've chronically had a problem with these pedometers if they're not accurate."

However, if a pedometer is accurate in counting steps, Thompson said it is fairly easy to convert those steps into calories burned. For example, if someone runs six miles, Thompson said it's quite accurate to assume he or she burned around 600 calories.

Pire said the GPS-based apps that mapped the specifics of runs, bike rides and other exercises would be a useful tool for a person who exercises regularly. But he still prefers a pedometer above all else because "it's not just for runners , it's not just for cyclers. It's about moving," Pire told MyHealthNewsDaily.

Apps to train by

GPS-based trackers and pedometers aren't the only way to measure your fitness achievements. A large market of health and fitness apps revolves around simultaneously measuring and motivating people to train.

Take the CardioTrainer, an app that got a nod in the New York Times' "must-have" Android apps of 2010. CardioTrainer does not include calorie counts, but it comes with GPS logs, as well as entries to track yoga and a variety of other workouts. The app can play motivational messages during workouts, and manage a music playlist to keep you moving.

On the other hand, some popular apps focus on a single training task, such the "Couch to 5K," which plays a training schedule designed to prepare a true couch potato for a 5 kilometer run through a walking-running regimen.

Established fitness companies often produce apps designed to be comprehensive libraries for the fitness buff , such as the Men's Health Workout app (iPhone), which includes 23 pre-loaded workouts and more than 150 available exercises.

Pire reviewed some of the more popular comprehensive libraries for workouts, including the Men's Health Workout app and the Nike Training Club app, and said many exercise guides in the comprehensive apps appeared to be accurate.

"It's real information I just don't know how helpful it will be to get people to move," Pire said. "You can also use a browser on the iPhone, and get online and go to a 100 different websites to get the same information."

But even if the comprehensive workout apps don't deliver more than some searches on the Internet can, Thompson said, if the app motivates you to move more, then it is a success.

"Anything that motivates anybody to exercise has got to be a good thing," he said.

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