No pain to speak of, leastways. And I've been at it over 38 years. Your mileage may vary, as does Malcolm Pollack's who, in his Pain, No Gain, reports:
I used to run. I never liked it much, but I did it anyway. I was never fleet of foot, and I never ran very far — two or three miles, usually, with the longest effort ever being only about six miles or so.
Mileage is indeed the key. Malcolm never ran far enough to experience what running is really about. He didn't take the first step. Arthur Lydiard, Run to the Top (2nd ed. Auckland: Minerva, 1967, p. 4):
The first step to enjoying running -- and anyone will enjoy it if he takes that first step -- is to achieve perfect fitness. I don't mean just the ability to run half a mile once a week without collapsing. I mean the ability to run great distances with ease at a steady speed.
That's one hell of a first step. But the great coach is right: you will never enjoy running or understand
its satisfactions if you jog around the block for 20 minutes four times per week. I find that only after one hour of running am I properly primed and stoked. And then the real run begins. Or as I recall Joe Henderson saying back in the '70s in a Runner's World column: Run the first hour for your body, the second for yourself.
I don't move very fast these days. I do the old man shuffle. But I've got staying power. Completed a marathon at age 60. Enjoyed the hell out of last week's 10 K Turkey Trot. Surprisingly, the satisfactions of running are the same now as they were in fleeter days.
To avoid injuries, limit your running to two or three days a week and crosstrain on the other days. I lift weights, ride bikes, use elliptical trainers, hike, swim, and do water aerobics.
And don't forget: LSD (long slow distance) is better than POT (plenty of tempo).