Hi all First post. Just started running at beginning of December to train for a half marathon in March. I found running 1.5 miles really hard then but am now up to 9 miles on my weekend 'long run' at a 8.25 pace. My concern is my heart rate. I feel that I am running slowly but according to my Garmin I am doing about 90 percent of my runs in zone 5 (170bpm average). At 44 years old is this ok? If you do the 220 minus your age then it seems too high and if I trained in zone 2 like I have read somewhere then I would be walking!!