I've recently managed to run a steady 5k on the treadmill two or three times quite happily but I'm concerned about my Heart Rate. My Max Heart Rate is (220-70) 150. I always warm up for five minutes and cool down for the same amount and when I finish my 36min run I feel great and not exhausted. But my HRM shows my HR to be 155-160 for about 25 min of the run. Should I be worried about this?