As she circled the track inside the Alaska Dome on Wednesday morning, Traci Falbo had been running nearly non-stop for 48 consecutive hours, her only respite a handful of naps that, combined, didn't amount to an hour of sleep.

Yet, inexplicably, having already covered more than 200 miles, Falbo accelerated her pace.

She covered a lap of the 413-meter track, unofficially, in 2 minutes, 23 seconds. Soon, she clocked a lap in 2:15. And then she reeled off a couple of 2:06s.

"Traci! Traci! Traci!'' fellow ultramarathoner Ed Ettinghausen chanted as Falbo passed him.

Runners and spectators applauded and shouted encouragement each time Falbo passed the start-finish line, where an electronic timing mat logged her progress from the timing chip attached to her ankle bracelet.

Falbo's effort exacted its toll. Her upper body listed increasingly to her right as she ran. Her mouth opened wider as she gulped air. With about four minutes left in her 48-hour run, she collapsed into the arms of her husband, Mike, at the start-finish line. She was spent, physically and emotionally, and she cried, seemingly from both exhaustion and elation.

Read more: Traci Falbo literally ran until she dropped, and seized 2 ultramarathon records