When Rob Jolles was a Boy Scout, the Maryland speed record for tying 10 required knots was 3 1/2 minutes. Jolles decided to better it.

He practiced and practiced and found a way of perceiving knots that his current roommate, a chemist, calls the "unified field theory" of knot-tying. Instead of tying one step at a time, Jolles made all the loops and twists at once, then pulled them taut.

When he tried for the record, Jolles had 10 rope strands laid out on the floor and a colleague standing over him to call the next knot as Jolles completed each one. "I was tying so fast I couldn't stop to think what was next," he said.

He finished the 10 knots in 29 seconds.

The knot-tying episode is one example of Jolles' competitiveness and the lengths he will go to when determined to accomplish something.

Another example of his drive can be seen in an incident that occurred two years ago, when someone dared Jolles to run a half-marathon. He had never run competitively, nor did he jog. He planned four days of training, but on the third he ran 4 1/2 miles and was so tired he barely could walk on the fourth. He didn't have running shoes, so he borrowed some and wore three pairs of socks to fill them.

Two thousand runners participated in the 13.1-mile race. Jolles finished 250th.

Jolles found that running provided the ideal outlet for his competitive spirit.

He had always loved sports and gravitated to high-visibility games at Churchill High School in Potomac and the University of Maryland. Unfortunately, baseball, basketball and football coaches aren't very enthusiastic about guys who are 5-feet-6 and weigh 110 pounds, as Jolles did as a high school senior. In intramurals "I kept getting beat up," he said.

He spent his youth listening to what couldn't be done. Long-distance racing showed him what could be done. He liked the scene at the end of a marathon best. "People are holding the runners up. They're bleeding, they're dragging a leg. I tell you, it sends chills through you."

On Feb. 6 Jolles hopes to drag himself, perhaps stumbling and bleeding, over the finish line of one of the world's most insane survival competitions -- the Iron Man World Triathlon in Hawaii. He sent in his $85 entry fee and began training in mid-August, when he drank his last beer for half a year.

The triathlon is an all-day, 140-mile event performed before the cameras of the "Wide World of Sports" television program. The triathlon comprises a 2.4-mile ocean swim, a 111-mile bicycle race and a marathon -- the only event in which Jolles has experience. He ran the Marine Marathon in Washington last year in 3 hours 19 minutes.

The triathlon ought to be perfect for Jolles, whose sporting interest these days is how far he can push himself. "I don't quit. I don't care about winning or losing. When I was young, I never won anything. But I never quit."

Jolles, 24, is an administrator for the New York Life Insurance Co. and lives in a Reston condominium. He still has the same slight build and determination he had as a Boy Scout.

To prepare for the triathlon he has engaged a full-time trainer, former tennis professional Charles Monroe, whom he calls "Angelo" after fight trainer Angelo Dundee. He also has friends working with him who are specialists in long-distance swimming and bicycling.

His training involves running about five miles six days a week, bicycling 10 miles twice a week and 40 miles on Sunday, swimming three-quarters of a mile twice a week and working out with weights three times a week. Two weeks ago he ran a 13-mile race one morning and played two sets of tennis that night.

His goal is to be able to do half what the triathlon calls for in a day and not be exhausted. "Then I'll know I can do the whole thing with the adrenaline of the race," he said.

Do any of the events, which run consecutively from dawn until whenever, worry Jolles?

Only swimming, he says. "Right now, I'd say I am a survival swimmer. But if I come out of the ocean alive, I'm going to finish this thing."

Last year 350 people entered the triathlon and 200 finished. The winning time was a little over 10 hours; the slowest about 24. Jolles hopes to finish in about 14 hours, "but that doesn't mean I'm not going there to win."

One thing that does worry him is that "probably all 350 last year were people who were damned serious about it," yet 150 still dropped out. It concerns him because "if I do quit, I know I'd have to go back and try again. And I don't want to ever have to go back."

Jolles is an engaging, very intense individual who gets so excited when he talks that he outruns the note-taker. You almost believe him when he says, "The only way I'll quit this is if I pass out, and then it'll be a medical miracle, because I'll get up off the operating table."

Is he trying to prove something? "Not to anybody but me," he says, "and I don't plan to run around afterwards with a flag saying, 'Look what I did.' "

When Jolles sent in his entry fee, he told race organizers to list him on the program as Rob (This-Kid-Won't-Quit) Jolles. "If I don't quit in this thing, I'm never going to quit anything."

So what's next?

"I don't know. Bring 'em on. Maybe this will get the monkey off my back. It'll be a big confidence-builder for me. When you do the ultimate, then you can just sit back . . . "

His eyes narrowed. "It's frightening to think how good I'm gonna feel when I finish this race."