Six runners who braved a half marathon in Pasadena amid record-breaking temperatures Sunday morning were hospitalized for heat-related conditions, authorities said.

Paramedics treated 15 people for heat-related injuries along the course of the 3,500-runner race, mostly near the end of the 13.1-mile route, said Lisa Derderian, a spokeswoman for the Pasadena Fire Department. Of them, six were taken to the hospital in serious condition, she said.

Derderian said that at least two of the seriously injured runners were suffering cramps, stumbling over their words and fading in and out of consciousness. Temperatures were already in the low 80s in Pasadena when the race began at 6:30 a.m. and later reached highs of near 100.

"A lot of what they didn’t take into account is the radiant heat from the black asphalt," Derderian said. "No matter how much you train, it’s hard to acclimate your body to these conditions."

Paramedics on bikes were stationed along the race course, and air-conditioned "cooling" buses awaited participants at the finish line at Pasadena City College.

Temperatures in the Los Angeles area are expected to slowly cool during the week, but will still remain above normal levels, according to forecasts. Excessive heat warnings for the San Gabriel and San Fernando valleys and the Santa Monica Mountains were canceled Sunday afternoon. 

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victoria.kim@latimes.com