It's a good time to be a running geek. Just a few decades ago, digital watches still seemed like a pretty neat idea; now heart-rate monitors and GPS watches are standard, and new gadgets analyze your stride and cadence, compute your power output, or measure your lactate levels, all in real time midrun. But how do you pick out what's useful without drowning in an ocean of data? Here are some guidelines to keep in mind. Read more on RunnersWorld.com.