It started out innocently enough.

My partner offered me his old Fitbit when he got his replacement, which the company had shipped free after he emailed them saying his had worn away on the edges.

I said I'd try it on for kicks.

(A Fitbit is a wearable fitness tracker you wear every day, like a watch.)

It was great at first. I was taking the stairs more often at work, walking outside to make phone calls, messaging back and forth with other friends who had Fitbits, and even joining in on the occasional Weekend Warrior competition, a minimarathon you do with your friends to see who can get the most steps in one weekend.

This type of behavioral change works for a lot of people, and for some, it's even helped them lose weight and reach other fitness goals. For me, not so much.

10,000 steps

I got my first warning that Fitbit wouldn't work for me on my second day wearing it, though I didn't realize it at the time. I was walking along when suddenly my wrist began to vibrate violently. I looked down to see the band flashing "10,000" in bright white numbers as diagonal stripes crisscrossed across the rectangular screen.

The tiny party on my wrist meant I'd reached the daily 10,000-step goal, the magic number many people with wearable fitness trackers are working toward. While it made me feel great at first, the feeling quickly spiraled out of control.

The 10,000 number isn't completely random: The American Heart Association backs it as a benchmark for improving health and reducing the risk of heart disease, and the workplace-health organization Global Corporate Challenge has conducted studies whose outcomes seem to support the 10,000-step approach. Many participants in one of its recent studies saw significant improvements in weight, blood pressure, waist size, and BMI.

When the vibration stopped, I immediately texted my partner, Chris, to report my progress. "10,000 steps!" I texted him, adding, "W00t. This is fun."

View photos fitbit friends ranked More

Feeling accomplished, I kept walking, only to find myself glancing down every few minutes at my wrist to see how many steps over 10,000 I had walked.

I watched as the screen ticked off each step: left, right, left, 10,001, 10,002, 10,003.

Next, I pulled my phone out of my pocket to check the Fitbit app's dashboard. There I could see my other friends' statistics as well as my own.

I had done my 10,054 steps, but I was still behind three people!

Tracking my exercise and food

I was feeling defeated, and my mind began to wander to ways I could match my friends.

"What about that yoga class I did yesterday?" I thought to myself. "Shouldn't that count?"

Lucky for me, Fitbit is way head of me on this one.

While its basic wrist tracker (the "Charge") still can't tally all your activity — the company is still working on this and recently came out with a cardio version of the device, the "Charge HR," which can give you a guesstimate of your physical activity based on heart-rate measurements — you can add your own activities manually by tapping "track exercise" on the phone app's dashboard.

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