target heart rate at rest

I started running about 6 weeks, and am having a difficult time keep my heart rate below 142. Usually I'm in the range from 142 to 150. Is it safe? My resting heart rate is around 52. I want to start to train for a marathon and a half and wanted to know what a good heart rate at the destination. I am a cyclist and 140 to 150 beats per minute is a little higher than usually as the goal of an aerobic base, but it feels like I almost have to walk to get my heart rate down to 140. Oh yes, I'm 39 btw.

The "rhythm target heart "in some respects is a thing of the past. Here's why, 20 years ago was as big as the 4 food groups, but with the evolution of thought in sport the rules have changed. Initially it was believed that about 70% max (heart rate) should be your goal (maximum fat burning and cardiovascular health). What we have learned since then is training at a higher rate is safe and if you do not burn the highest percentage of fat (which is 70%), the total calories burned is higher (fat + carbohydrate) ... in other words, a more difficult exercise. Chances are if you are working above that the 70% target "," your heart rate tells me you are getting a better cardiovascular fitness and burn more total fat than you would in a 70%. Keep in mind, the best judge for the rate of a "target" is not taking your heart rate while working out, but rather how it feels (as 're breathing hard, how hard we're sweating, how quickly you recover, etc.) The conclusion is that it is safe to train over the "rules" if you are more in tune with your body and destroy the results of what was thought could be done 20 years ago.