Milton, Ont., octogenarian and champion runner Ed Whitlock felt "great relief" upon crossing the finish line of Toronto's Scotiabank Waterfront Marathon in record time on Sunday.

"I had real apprehension about how I was going to finish at around halfway," Whitlock told Metro Morning host Matt Galloway.

Despite his fears, the 85-year-old Whitlock still managed to set a world record for his age group Sunday. He finished the marathon in just three hours, 56 minutes, and 33.2 seconds.

Still, Whitlock said he wasn't entirely happy with his performance.

"My goal was to run around 3:50," said Whitlock. "Things fell apart in the second half of the race."

Compared to his previous world records, Whitlock said his accomplishment Sunday was less impressive than his earlier record, set at the Toronto marathon 12 years ago when he was 73 years old. He ran that marathon in just two hours and 54 minutes, a record that still stands today.

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Whitlock trains at the Evergreen Cemetery in Milton, Ont. (Nathan Denette/Canadian Press)

Whitlock started running as a teenager, but stopped when he moved to northern Ontario at the age of 21.

"There was no running up there in those days," quipped Whitlock.

"I didn't start running again until I was 40, so I've been running more or less continuously from 40 up to my current age."

Whitlock said the incentive to set records in his age group keeps him running.

"To some extent you're always happy when you've reached another milestone of five years older," he said.

Seasoned runner, seasoned running shoes

And Whitlock's running shoes have reached those milestones along with him. In Sunday's marathon, he said he wore a pair he's had for around 20 years.

"I wear them well past their due date," said Whitlock. "I'm not a fan of the current shoe design, and I have a small supply of this particular model of shoe."

'I'll keep running as long as I can'

Setting world records comes at a painful price, Whitlock revealed.

"My legs are shot today," Whitlock said. "I seemed to be OK yesterday after the marathon, walking around and that sort of thing, but rigor mortis has set in now."

Whitlock said he doesn't know when his next marathon will be.

"It depends how my training goes," said Whitlock. "One never knows when one has run one's last race, and I'll keep running as long as I can."

With files from Metro Morning