SACRAMENTO, Calif. — When Jon Mead, a devoted cyclist, visits a new city, he goes right to his smartphone app Strava to find the best bike routes. In Sacramento, Calif., 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 enough runners cover enough miles.

MapMyRide, MapMyRun, Livestrong, Run4Good, MyFitnessPal – they’re all 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 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-sized, 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, according to the report.

Ale Lauth is a senior health educator for Kaiser Permanente in the North Sacramento Valley region. She has witnessed the trend first-hand in her role as wellness guru for hundreds of Kaiser employees and physicians.

"We’ve definitely seen their usage increase," Lauth said. "The apps have come a long way, and they’re constantly upgrading."

They are also 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, CuresA-Z, not to mention a host of downloadable apps such as OvulationCalendar that help women track their menstrual and fertility cycles. And, yes, there are apps with tips for carrying on when that fertility cycle is spot on.

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.

The next phase is already in the works: apps that will transform your smartphone into a regulated medical device. Think phones as electrocardiography, or ECG, machines that can detect abnormal heart rhythms and determine if a patient is having a heart attack.

Such clinical apps will not go forward without approval from the federal Food and Drug Administration. Already, U.S. Rep. Mike Honda, D-San Jose, is working on a bill to establish a new FDA Office of Mobile Health designed to regulate health apps.

In the meantime, the private sector is leading the charge at Health 2.0-inspired code-a-thons, live events where developers gather to build apps and tools for improved health care. A topic getting prime billing at the International Consumer Electronics Show in Las Vegas this January: "The Human Body: The Next Digital Revolution."

For now, most physicians are happy to see patients using simple apps to motivate them to exercise, eat well and lose weight.

MyFitnessPal has emerged as one of the more popular apps in this category, allowing users to set weight loss goals then diligently chart calories consumed, calories burned and poundage. Lauth, of Kaiser Permanente, said dozens of her charges use MyFitnessPal, getting into the swing of competition when they add friends to their wellness social network who can track each other’s progress — or lack thereof.

"These are great motivators," said Lauth. "When you hit your goals, you and your friends see the results."

Others in this category flash smiley-faces or other positive on-screen icons as rewards. They also offer pre-programmed verbal pats-on-the-back.

Says Lauth, "It’s like they are saying, ‘You are fantabulous!’"

Scribner, who helps Fleet Feet customers gear up for their runs, says she likes the social network aspect of workout apps.

"You can compete with your friends over your course, and it shows your elevation," she said. "Simply hit go."