A trial of fitness measurement devices leads a reporter to eat more donuts.

Time for a lunchtime jog. I plan to try out a brand-new Jawbone UP, a black bracelet designed to track my fitness in different ways – how far and fast I go, how many steps I take, how many calories I burn.

I open the package and realize it I need to charge it and call customer service to update the software. While I wait, I decide to eat a leftover slice of pizza from the Weekly fridge. After all, I’m not being measured yet.

I go running, swimming or hiking to tune out the world and the constant ping of electronics. I relentlessly mock my partner’s GPS-based Android app, whose female voice urges, “Let’s get started” at the beginning of a run. I am annoyed by her presence and her proclamations of our mile split times, but I am delighted to check how far and fast (or slow) I’ve gone at the end of a run.

So I was open to trying the latest iteration of personal fitness devices, unobtrusive clip-on bracelets designed for near-constant wear. Both Jawbone and FitBit models serve as pedometers and target a 10,000-step-a-day threshold, “the magical number,” according to FitBit’s blog.

“It should be enough to reduce your risk for disease and help you lead a longer, healthier life,” the blog states.

With that in mind, I undertook a few days wearing the UP ($129.99) and the FitBit Charge ($129.95), measuring my steps, my workouts, my sleep patterns.

The morning of my first full day with the UP, I go for a run I’ve always believed to be 4 miles. I’m disappointed to learn it’s just 3.8. But the steps I’ve taken are enough that by 10:30am, as I walk to the office lobby, I hear an alert on my phone, via a bluetooth-connected app. I’ve reached 92 percent of my 10,000-step goal for the day. It’s mid-morning, and there are still donuts on the counter. I decide I’ve earned it, and help myself to a chocolate glaze.

The effect is counterintuitive. Personal fitness trackers are supposed to be motivational. But all it’s motivating me to do is to eat more pizza and donuts.

The pedometer rewards me for simple things like puttering around the office. One weekend day spent birdwatching with a friend – when the physically hardest thing I did was raise the binoculars – set my FitBit record to date: 19,223 steps over 7.64 miles. I did not break a sweat.

“For a lot of people, [personal fitness trackers] tend to be a distraction,” says Monterey Sports Center Fitness Manager Bill Rothschild. “Rather than focus on the workout itself, they focus on the technology support.”

For me, the most intriguing opportunity was a look at my sleep patterns. The devices measure my “active” versus “restless” sleep based on how much I move my wrist, and how many minutes it takes to fall back asleep after I wake up in the middle of the night.

The results seem accurate, if not enlightening: I spend about half the night sleeping deeply, or at least unmoving, and half the night restless. They highlight how much time I waste lounging in bed and reading the news on my phone in the morning before actually getting up and earning my 10,000-step badge.

As for measuring my workouts, I seem to get a lot of credit for doing nothing, and less credit than I think I deserve for working out.

But it works for a growing number of people, or at least it lets those people report impressive numbers. One Sports Center client used a tracker to keep off 130 pounds. And Salinas Valley Memorial Hospital’s annual 10-week exercise challenge, which launches Feb. 2, is all about tracking minutes of activity.

Last year, nearly 3,000 participants logged more than 6.3 million minutes of aerobic exercise. I wonder how much was slow-moving birdwatching.

“What you miss with the FitBit or Jawbone or other devices is that human, personal connection,” Rothschild says. “Having a portable device that gives you that feedback is not the same as a human being. And it does not necessarily have to be a trainer. A buddy helping make sure you show up at the gym is something you just can’t get from a device.”

Predictably, the fitness director recommends personal trainers over the devices that could replace them. But Rothschild’s lack of emphasis extends to the Sports Center’s clientele. “[Trackers] are not a big presence in our facility,” he says.

In fact, by way of a remodel, the Sports Center gym opened a new “core zone” Jan. 2, effectively an expansion of low-tech open floor space where clients can work on their abs and back muscles. And all those fancy settings on the cardio equipment? Most people at the gym don’t use them, Rothschild says.

They might be doing just as well. A Jan. 8 study published in the Journal of the American Medical Association found that wearable fitness trackers are mostly purchased, and mostly beneficial, to people who already have healthy habits – specifically, the wealthy and the young.

But even for the most well-intentioned, getting healthier is often more complicated than collecting data.

“The notion is that by recording and reporting information about behaviors such as physical activity or sleep patterns, these devices can educate and motivate individuals toward better habits and better health,” according to the JAMA study. “The gap between recording information and changing behavior is substantial, however, and while these devices are increasing in popularity, little evidence suggests that they are bridging that gap.”

The package of the Jawbone UP promises you will “get to know yourself.” I learn something I already knew: I can tell what feels right for my body, and I’ll do it whether or not a device tells me I’m supposed to.

That intuition, unscientific as it is, feels more accurate than any dataset.

For more about FitBit, visit www.FitBit.com; for more on Jawbone fitness trackers, visit www.jawbone.com