Zeizel is working in Afghanistan and training for the Boston Marathon on April 19 to raise money for cancer research. He turns 55 on Monday, and his knees hurt.

Training for any marathon is brutal enough, but Zeizel must do his roadwork indoors alongside younger, fitter runners — warriors, he calls them with immense respect — elbow to elbow, running for hours in cramped quarters.

They cannot run outside for two reasons — one, the “dark, gritty air,” fecal matter and bits of rubber tires burned to heat homes; two, the Taliban lurking out there somewhere, more than glad to pick off some fools running on the rocky terrain nearly a mile above sea level.

So the runners stay indoors, at a base somewhere near Kabul. Zeizel is training with an immediate purpose. On Patriot’s Day in his adopted home, Massachusetts, he will run his 17th marathon, all but one for the Dana-Farber Cancer Institute.