Boston set for heat

"If the temperatures reach certain levels, running will put even the most fit athletes at risk for heat injury," the Boston Athletic Association said in an advisory on Saturday.

The temperature on race day is expected to hit 87 F (30.5 C), a condition especially trying for slower runners who will be out on the 26.2-mile (42-km) course for many hours.

"If you have underlying medical problems, such as cardiac disease or respiratory disease, think about not running," said Pierre D'Hemecourt, the BAA's co-medical director. "If you have a cough or cold, or had recent gastro-enteritis, don't run."

He said participants should be vigilant about headaches, dizziness, confusion, fatigue, nausea or vomiting, which can be symptoms of heat exhaustion or heat stroke.

"This is not the day to be running your personal best," D'Hemecourt said at a press briefing.

Deaths have been rare at the Boston Marathon, possibly because entrants tend to be experienced runners. The most recent death was in 2002, when a young female runner collapsed from hyponatremia, an electrolyte imbalance that can be caused by drinking too much fluid.

The race, which is expected to draw more than 27,000 people, starts 9 a.m. EDT (14:00 UK time). But the slowest wave of runners will not leave until 10:40 a.m, when temperatures could already be above 70 F (21 C).

The hottest Boston race is believed to have been in 1976, when the mercury reached close to 100 F (38 C).

For top runners, many of who come from African countries with hot climates, the oppressive heat is not likely to pose as much of a problem.

Kenyan Caroline Kilel, who will defend her 2011 women's Boston title, said she does not expect hot temperatures to make much difference to her race.

Organizers are boosting supplies of water and ice along the course, and have arranged additional ambulances and medical sweep buses. Red Cross stations will double and triple up along the race route, and fire departments will have spray hoses in places for runners to cool down.

Entrants have the option of deferring to next year's race if they choose not to start on Monday.

Some 5,000 spots are reserved for runners representing organizations such as charities, sponsors and municipalities.

They are often slower and less experienced than those who qualify by posting certain times in other races.

"If you are an inexperienced runner, you should consider very carefully if you should run or not," said Tom Grilk, the BAA's executive director.