I am not new to running/jogging, but I have never ran more than a 5k. I generally run about 8-10 miles a week to stay in shape. Lately I have noticed about half way through my usual 1.5 my legs and arms begin to feel extremly heavy and tired. I am not sure what is causing me to feel this way, has anyone else experienced this, and if so what did you do about it?
If you have been running harder/faster then usual, you might have heaviness in your limbs if you haven't recovered from your previous run. I also recall the run (not a race) a couple of years ago when my legs felt really heavy on the second tenth of a mile. That remains my fastest ever run at that distance.
I find that my legs feel really heavy, and my times are really slow, if I run after being on my feet for several hours (I usually run in the morning, but occasionally my only opportunity is after work).
You don't give your age or health status, but it could be a medical issue -- anemia, or circulation problems.
You could be *mentally* over-trained, and need a short break.
I find that the best training strategy, even for general health, is variety. Alternating the length of your runs, your speed, workouts, shoes, places that you run - you'll find that you're always excited to run and it's never a chore.
But specifically, you may want to do some longer runs 1-2 time a week. You'll find that your legs always feel good on a short run when your body can go longer!