Heat slows Boston Marathon field

Temperatures that rose into the 80s slowed the field at the 116th Boston Marathon and may have convinced as many as 4,000 runners to sit this one out.

A total of 22,426 runners started Monday’s race in Hopkinton in temperatures expected to be as high as 84 by the time the last of them finish their 26.2-mile trek to Boston’s Back Bay. That’s about 84 percent of the registered field of almost 27,000, with many of the no-shows expected to take race organizers up on their offer for a deferment into next year’s race.

The largely unprecedented offer was issued in response to forecasts that called for temperatures rising from 69 at the start and had risen to 81 by the midpoint of the race.

The heat didn’t seem to be a problem for Canadian Joshua Cassidy, who won the men’s wheelchair race in a time of 1 hour, 18 minutes, 25 seconds that is the fastest in history.