When Joan Ullyot, a physician and an accomplished runner, published her book “Women’s Running” in 1976, she took on a daunting set of traditional ideas that boiled down to one admonition: Women should not run long distances.

They were not physiologically built for it, women were told. Compared with men, they typically had higher body fat, less muscle bulk and lighter bone structure, factors that should discourage them from engaging in long-distance running — or so it was believed. Moreover, many authorities in the field warned that extended running might harm women’s reproductive organs.