You're jogging at a steady pace, enjoying your favorite music through your headphones. Your breath is short and your heart is pumping. Your legs feel like they couldn't carry you any faster.     And then you hear the groan of a zombie over your right shoulder. You must run or be eaten.     The zombie apocalypse  isn't upon you. You're just taking part in the latest fitness craze--Smartphone apps that make a fun and interactive game out of your daily workout.     Software developers are taking advantage of Smartphone's advanced technology--GPS, accelerometers  , MP3 players--to create "immersive" fitness games that appeal to both desperate and reluctant exercises.     It's part of an overall trend in the fitness industry toward making your daily workout "a fun experience rather than something you have to do," said Jessica Matthews, an exercise physiologist for the American Council on Exercise. "We are attempting more "play" opportunities as opposed to working out, basically getting people to move and having fun while they are doing it," Matthews said. One popular fitness game app, Zombies, Run!, places you in the role of a supplies runner for a walled community trying to survive against the walking dead.     During your run, the game's surprising complex story unfolds through your headphones. You "pick up" supplies for the community as you jog along. At certain intervals, you're warned that zombies are nearby, and if you don't pick up the pace, you'll have to pitch  some supplies to keep from being caught.     The game doesn't end once your jog is over. After your workout, you can use the supplies you picked up during your running to fortify your community. The GPS statistics from your run are uploaded automatically to the game's website, so you can review your average speed and the estimated calories you burned.     Teemo, Nexercise and Fitocracy all allow you to post your latest workout to share with friends. Some games have you work with friends to reach a common goal--completing a relay race, for example--while others encourage competition.     "That's another big area, having that social component," Matthews said, "Having social support of some kind is a critical factor in adhering to an exercise program. For some people, having that friendly competition or the feeling of being on a team can help them stay motivated." Smartphone's advanced technology is used to   _  .
steady the jogger's pace make exercisers' hearts pump control the rate of workout create a virtual health game