Smartphone 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 sleep trackers:

Plenty of people use their smartphones as alarm clocks, as evidenced by the New Year's Day foul-up in which three L.A. Lakers players missed practice because of glitch with the iPhone's time feature, and lost a game later that day.

But some technophiles use their smart phones to get the most out of sleep .

The Sleep Cycle Alarm Clock (iOS) app uses the iPhone's accelerometer to measure a person's movement throughout the night. The developers encourage users to put the phone on the mattress near the head of the bed, and clock-in just before falling asleep. The app then senses movement through the night. When a person's movements increase, supposedly indicating a light stage of sleep, the app's alarm goes off to wake them up.

Dr. Lisa Shives, medical director of Northshore Sleep Medicine in Evanston, Ill., said the concept for the app was intriguing, but would work best if sleep experts develop the technology to measure sleep cycles by movement alone.

"The way we do it is to use brain wave data," Shives said.

Sleep experts have experimented with devices called actigraphs, also known as actimetry sensors, to estimate circadian rhythms for years. But Shives said a person needs to wear the device for about a week in order to establish a baseline of normal movement for the individual.

"More research has to be done into the normal amount of motor activity for various stages of sleep," Shives said. "There might be a little bit of correlation," between a person's movement and their sleep cycle , "but you need a very sensitive instrument. And it has not been really codified."

Moreover, Shives said the app seems to be pinned to an assumption that it is best to wake out of stage I sleep, or the lightest stage of sleep.

"The one thing that sleep doctors would agree to is probably that if people are yanked out of deep sleep, they're going to feel worse. They're going to feel groggy for a few minutes," said Shives, who is a member of the American Academy of Sleep Medicine.

However, closer to the end of the night's rest, most people naturally transition from deep sleep to the lighter stage of sleep, called stage II, and then to REM sleep, in which people dream but do not move very much.

Shives said a person may drift out of REM briefly into stage I sleep and move a bit, before falling back into REM and awakening naturally.

"It's not a widely held axiom that it's better to wake up at a light stage of sleep rather than REM," Shives said.

Shives told MyHealthNewsDaily she would wait for more studies to endorse these types of sleep apps, but "there's no harm in trying something like that, and seeing if you feel better if you wake up."

However, other popular sleep apps that allow users to track their sleep over time give Shives pause.

Apps such as the SleepBot Tracker let users clock-in when they fall asleep and automatically clock-out when they turn off the alarm. The app then tracks the hours slept, and sleep debt , over time. SleepBot was developed by college students for people trying to catch up on sleep after working late or all night.

On one hand, Shives said, many people come to her sleep clinic with misperceptions of how much sleep they actually get, and such an app could reassure them.

"They come in and complain of insomnia, and maybe you find out that they're sleeping more than they think," Shives said. "Sharing that with them can make them feel more empowered."

However, Shives said, counting the hours until you fall asleep can be detrimental for true insomniacs, not those just looking to catch up on sleep after midterms or a child's illness.

"It's going to still be your estimation of how long it takes to fall asleep. And the last thing a person wants to do is to keep looking at the clock as they fall asleep," Shives said. "This kind of application, in the hands of the wrong patients, just leads to an obsessive worrying and anxiety."

In any case, sleep apps are part of a larger trend to log daily activities to improve health.

The accelerometers and GPS systems built into many smartphones make them an easy platform to develop apps that track your steps, your bike route, your yoga schedule and more.

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