Joe McGinniss, 68, has written several political books including works on former president Richard Nixon and on Alaska.
Six months: Palin is said to have had an affair with Brad Hanson, one of her husband's colleagues Mrs Palin got pregnant with Todd and they eloped in August 1988.
Both Mrs Palin and Mr Hanson have denied the allegations.
The next day, a Saturday, she and Elijah ran again.
That report said running makes people happier, helps them lose and maintain weight, strengthens knees and joints, keeps a person mentally sharp, reduces the risk of diseases such as cancer, and adds years to life.
The writer gained notoriety aged 26 when his first book about how Richard Nixon marketed himself, titled The Selling of the President 1968, became an overnight success — leading to him becoming the youngest living author with a book on the New York Times bestseller list.