The pair leads a strong contingent of runners that will compete in the race's 119th edition on April 20.
We asked an elite runner, a nutritionist and a coach how they fuel for 26.2.
The 31-year-old is healthy again and gearing up for the Rock 'n' Roll Philadelphia Half Marathon on September 21.
Try this workout from coach Brad Hudson to boost your fitness.
Kenyan Moses Mosop, second at Boston in 2011, also announces withdrawal from race.
Or are you satisfied with performing to 90% of your potential but with less chance of injury?
A strong international field will line up in The Windy City on October 13.
Seriously, everyone's doing it. Join the crowd.
The Olympic silver medalist booked his ticket to Moscow.