FOR Conrad Kiffin, running a marathon is like starring in his own personal video game. Every mile, he sneaks a look at the global positioning system on his wrist to see if he’s keeping up with an imaginary rabbit going at his target pace.

“If I see the pacer running away from me, I know I have to go harder,” said Kiffin, 41, a photographer in Manhattan. “It’s very video-gamey.”

Staying on pace is a hard-won skill for marathoners. Only the best are able to estimate their speed with nothing more than a head-to-toe check of how they feel. For those who haven’t honed this sixth sense, GPS units and heart-rate monitors help them avoid the 11th-hour meltdowns that follow too-fast starts.

At the New York City Marathon today, many of the 37,000 participants will be wired and, in some cases, wireless including Paul Kaye, from Cape Town, who plans to run with a cellphone strapped to an arm with software that plays music and beeps to let him know if he’s on pace.

Lance Armstrong, the seven-time Tour de France champion, will wear Nike+ shoes with sensors made to send pace data to his iPod nano. Dino Farfante will carry an MP3 player and, strapped to his arm, a GPS unit that gives oral updates on his speed.

And of course there are the legions of iPod users who will run with white wires snaking through their T-shirts. And the cellphone and camera carriers, who will be chronicling their experience for posterity. Every competitor will wear a shoe with a chip to record their progress, and can send e-mail updates every 5 km to spectators who subscribe to the service.

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