I have been a really consistent high/mid 50's HR for years now and in the past month it has dropped down to mid 40's. I know that resting HR responds to conditioning but this feels like a fast change to me. I have increased my strength training and am doing slightly less cardio as I'm focusing on shorter, faster events but other than that not much has changed. I know people out there do a lot more work with HRM than I do, and you are all athletic so I figured that you are not a bad sample population to ask. Has anyone else had their resting HR change that quickly?