At my weigh-in this past month, I was thrilled to see I'd lost a few pounds, but annoyed and baffled by the fact that my body fat percentage hadn't budged. What's going on? My trainer, Lauren Kern at Equinox, explained that my new workout regime might be the culprit. Lately I've been so focused on increasing how far I can run, that some of my strength training sessions have gone by the wayside. So while I have been blasting lots of calories and fat while pounding the pavement, I've also lost some muscle mass, which not only makes me look less toned but also means I'm burning fewer calories during the day. Swapping out a couple of my weekly runs for a strength-training class should be just the thing to get my percentage unstuck in time for next month's measurements.