Running can also be very high impact on joints and if a person hasn't moved around much for quite some time might be asking them to do more than they are ready for.
Recently started running again. Hadn't run in in close to a decade, but I got back into it really quickly. However, after only a few weeks of running, I developed symptoms similar to compartment syndrome in my left leg, and now I can't run for more than 30 minutes every other week without getting really sore. I was really getting into it, too.
Swimming, Rowing, elliptical, cycling, or StairMaster are safer and offer similar health benefits.