I think the trick is to have obese/chemo people to run before they become obese/chemo people, for preventative benefits and to engrain the habits early on.

In the case of obese people, there is an argument that due to the high impact nature of running, other forms of exercise may be preferable (imagine the force of a heavy bodyweight crashing down on a person's joints many,many times over the course of a run, ouch). Perhaps cycling or swimming would be more advantageous to the overweight population. Of course, the benefits of walking are often understated, but certainly the humble stroll could impart a myriad of benefits to those of ill-health.

I wonder if the same health benefits can be had from involuntary running :P