I have a Garmin Forerunner and have been using it for a few months now. I've also lost about 20lbs since I started running regularly. I'm pumped about the weight loss but unfortunately I've adjusted the Heart Rate Monitor strap to the tightest level and it falls down when I'm running now. I had to wedge it under my sports bra elastic to keep in place today but it doesn't always stay put. I'm a petite person but I don't feel like I'm abnormally small, so I'm surprised I can't adjust it tighter. Has anyone come across this problem and manipulated it somehow? Thanks so much!
My bra band size is 34, so reasonably smallish, and I've never had that problem. I usually wear mine tucked under the band of my bra, otherwise the bra band pushes it down.
I have had problems with the garmin heart rate monitors too. I just got the 620 and I have it as tight as it will go. I stick it mostly under my sports bra to keep it in place.