without all the injuries and pain that go with running. No pain, no gain. My standard old school response. Running does push one to the limits while strengthening the body. At 53 years old,I continue to run. Injured only by blisters from lousy shoes.
I was in the Marines where "no pain, no gain" was the mantra. I respectfully disagree with that now. Physical fitness need not involve pain. I actually consider myself in better physical shape today then in my Marine days because I'm eating better too. In the Marines, I had a terrible diet. When I wasn't in the mess hall, I'd eat nothing but Twinkies, donuts, chips, cookies, etc.
Now if you are talking about "soreness", that's a different issue. I do get sore after a challenging walk or after doing a bunch of situps and pushups. But I don't consider that pain.