Scott Cameron, of Guelph, Canada, sprints ahead of the pack of runners beginning the second of three main waves of the 115th Annual Boston Marathon at 1 Ash Street, in Hopkinton, Mass., on Monday, April 18 in which 24,338 registered participants ran.  Cameron finished with a time of 4:03:33. (Junhee Chung/Boston University News Service)

Scott Cameron, of Guelph, Canada, sprints ahead of the pack of runners beginning the second of three main waves of the 115th Annual Boston Marathon at 1 Ash Street, in Hopkinton, Mass., on Monday, April 18 in which 24,338 registered participants ran.  Cameron finished with a time of 4:03:33. (Junhee Chung/Boston University News Service)