SACRAMENTO, Calif. — When Jon Mead, a devoted cyclist, visits a new city, he goes to his smartphone app Strava to find the best bike routes. In Sacramento, where he works at a Fleet Feet running-gear shop, the 24-year-old uses MapMyRide to track his course in an archive.

Bethany Scribner, a runner who also works at the fitness gear retailer, likes the apps MapMyRun and Livestrong, which tracks nutrition in a daily pie chart showing fat, protein and carbs. Saucony Run4Good is a favorite, too, said Scribner, 21, because the company donates to anti-obesity programs for kids if runners cover enough miles.

MapMyRide, MapMyRun, Livestrong, Run4Good and MyFitnessPal — they’re part of an exploding arena of health and fitness applications for smartphones. The trend, which falls under the umbrella of Health 2.0, an international tech movement grounded in San Francisco, is proving to be an obsession for programmers at code-a-thons, as well as users who get hooked on tracking their workouts, calorie intake and weight loss.

Among users, a pinch of competition, a social network of friends who sign up to share fitness scores, is all you need to make this an activity as additive as Twitter is for some and Facebook is for others.

The Pew Research Center, in a new report titled Mobile Health 2012, found smartphone owners in the vanguard, with 52 percent gathering health information on their palm-size, micro-computers. That compares to 6 percent of owners of regular cellphones, the report said.

In addition, Pew found 19 percent of smartphone owners have at least one health app on their devices, with exercise, diet and calorie-counting programs the most popular.

Overall, the proportion of cellphone owners who use their phones to access health data nearly doubled from 17 percent two years ago to 31 percent today, says the report.

The apps are constantly upgrading. They also are proliferating. Click on Apple’s health and fitness apps page and you’ll find iRunner, Fitocracy, Fitter Fitness, Fitness Buddy, Fitbit, Fitness Pro, miCoach, Abs Workout, RunKeeper, Virtual Trainer, and about 250 more.

And it’s not just fitness. There’s a parallel world of apps geared to other aspects of health and wellness: iTriage, iFirstAidLite, InstantHeartRate and CuresA-Z.

The medical community is embracing the trend, holding contests to encourage programmers to design disease-specific apps that doctors can “prescribe” to patients with heart disease, diabetes and other chronic conditions.

The American Medical Association has launched its own consumer weight app, and the U.S. Department of Health and Human Services Office of the National Coordinator of Health Information Technology held a contest in July for the best app to help consumers identify and reduce their risk of heart disease.