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.

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