health monitor device
Photo: Dan Saelinger
I spend, on average, 128 minutes in REM sleep per night. I require a minimum of 1,400 calories per day to stay alive. My resting heart rate hovers around 57 beats per minute but spikes to 65 when I'm answering e-mail or talking to my husband on the phone.

I know all this because I recently spent two weeks following my body's statistics with as many devices, Web services, and phone apps as i could manage at once. Inspired by a growing group of extreme self-trackers—people who attempt to quantify their everyday activities (everything from exercise to sleep to sex) in order to gain insight about themselves—I set out to answer two questions: Would monitoring myself inspire me to adopt a healthier lifestyle? And what would happen to my peace of mind if I turned my life into a data sheet?

Not long ago, this experiment would have been impossible without a team of lab techs and a ton of manual calculations. But today, thanks to cheap sensors and an explosion of gadgets and apps that use them, I have tools I never would have dreamed of, like accelerometers to detect my movement, and galvanometers to tell how active I am by measuring how sweat is affecting the electrical conductivity of my skin. What's more, I can see many of the numbers my sensors produce right on my phone.

I started my investigation with the same enthusiasm that often accompanies January 2 visits to the gym. I measured and recorded everything I consumed, right down to the grams of strawberries I added to my Greek yogurt in the morning. Each day I stepped on my Withings WiFi Body scale, a wireless-enabled device that automatically sent my weight and body mass index to my computer and phone so I could note trends. (Despite daily fluctuations, the numbers were relatively steady over time.) I strapped a wireless monitor to my chest and stuck a small receiver into my phone so I could see a chart of my heart rate while I jogged. (I now know exactly how many beats per minute mark the point where I feel like I might throw up.) At night the Zeo, a sensor on a fabric band that I wore around my forehead like a nocturnal Wonder Woman, measured my brain's sleep cycles. After I uploaded the data to my computer, an online coaching program made suggestions as to how I could maximize the quality of my time in bed.

It took only a few days to confirm that yes, self-monitoring does indeed change the way you behave. This is due to what's known as the Hawthorne effect: the tendency to act differently when you know you're being watched. It's the same phenomenon that makes you pedal harder in Spin class when the teacher turns your way, and it applies even if the only eyes watching are your own. Having good numbers made me feel good, so I adjusted my behavior to achieve them, whether it was by forcing myself to meditate so I could jot down 30 minutes in my log or pushing myself harder at the gym for the benefit of my heart rate monitor.

Like a kid who's paid to do her homework, I had less than pure motivations. But I was happy with the result: My weight was steady, I was exercising more and getting good sleep. Tracking, I noted gleefully in my journal, was fun.

It was also addicting. By the end of week one, I began to feel as if I were playing a game of Self-Tracking Whack-a-Mole: For every variable I managed to pin down, another possibility sprang up in its place. If I knew how much water I was drinking, shouldn't I also track dehydrating drinks like coffee and subtract them from my daily hydration total? If I knew how far I was walking every morning, shouldn't I map my routes so I could cover new ground each day? Couldn't I—shouldn't I—be doing more?

After two weeks, keeping track of my tracking was sucking up an hour a day. Still, I kept going. Despite having quadriceps worthy of a professional rugby player, I decided I needed an objective, numerical assessment of my fitness. I wanted to know my VO2 max, a measurement that indicates aerobic endurance based on how efficiently your body transports and uses oxygen. So, on a whim that seemed perfectly natural at the time, I paid a visit to the Performance Lab, a facility in Cherry Hill, New Jersey, that offers a range of athletic tests used to design personalized coaching programs for athletes.

The lab's director, a sports medicine physician named Michael Ross, fitted me with a plastic face mask that would analyze the amount of oxygen and carbon dioxide in my breath to help judge how well my body was burning energy. Then I stepped on the treadmill and began to walk, jog, and run as Ross reached over at regular intervals to increase my speed. After 11 and a half minutes, I was nearly at a sprint. One minute and 20 seconds later, my body decided that it had had enough. Before I knew what had happened, my feet were straddling the belt and I was doubled over, gasping for air. Technically, this meant I had done the test correctly: I had run until I could run no more. But the perfectionist in me wasn't satisfied. I wanted a better score.

"Maybe I should try this again," I thought. Or maybe there was another test I could take that would give me a different result.

That's when I realized my tracking had veered seriously off track. Gary Wolf, co-founder of a user's group called Quantified Self, had warned me this might happen. "The magic is not in how many numbers you collect or how devoted you are to collecting them," he told me over the phone. "The secret is using the data in a meaningful way." Tracking, he explained, should help you reach your goals, not be a goal unto itself. Not only had I lost sight of this, but I had crossed the line into obsession.

So i decided to take stock of my tools and keep only the ones that were actually helping me achieve the healthy lifestyle I wanted. I held on to the scale but ditched the food log. I accepted that I didn't need an app to tell me that I am consistently well hydrated. Instead of asking Ross for a redo, I used the test results to determine what heart rate I should target when I work out. And as I consciously winnowed my gadgets, I felt something return that, despite all my data, I hadn't realized I'd lost: perspective.

Next: 4 gadgets that can improve your health

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