Reflecting his Japanese culture, Tsuyoshi Yoshino politely asks you to remove your shoes upon entering his San Diego home. If the aspiring running coach has his way, you'll also take off your thick-soled running shoes for some of your workouts.

A former 2:43 marathoner, at Boston no less, Yoshino prefers to run with nothing between his feet and the pavement.

"It just feels natural," he said.

Yoshino, 33, first sampled barefoot running on July 28, 2005, the day before his birthday. Having read literature on the subject, "it just all made sense," he said.

His first 30-minute workout, on Balboa Park pavement, did not go well. On his laptop computer, Yoshino pulls up a picture that shows blisters stretching from the ball of his right foot all the way to the side of the foot. A portion sports a purplish-black hue.

"Oh my," Yoshino told himself. "This is going to take a long time to adapt."

Yoshino, though, is not easily dismayed.

He defied his parents' wishes that he become a mechanical engineer, leaving Japan at 22 to explore Australia for a year. Then he wandered about the United States and Europe another six months before attending Bridgewater State University in Massachusetts.

A rail-thin 5 feet 4 inches, 105 pounds when he came to the States, Yoshino quickly gained 30 pounds, courtesy of the school's carbo-loaded meal plan.

"It was all you could eat, and I was excited," he explained. "I'm drinking soda and eating French fries for breakfast."

To lose weight, he tried out for the cross country team.

Yoshino's odyssey brought him to San Diego in 2003.

"My main focus," he said, "was triathlon."

Within 10 months he finished Ironman Japan in 11 hours, 46 minutes.

As for his barefoot fixation, Yoshino earned a master's in exercise science at San Diego State. His thesis: "Potential Benefits of Barefoot Running."

Yoshino conducted a seven-week study with 10 participants who previously had not run barefooted. The subjects started running barefoot twice a week for five minutes, building up to twice a week for 20 minutes.

Among Yoshino's findings:

- Oxygen consumption increased for the runners. Yoshino theorizes that because barefoot runners land on their forefoot rather than their heels, they must run more efficiently, thereby using more oxygen.

- The force applied to the runners' feet was less than when running with shoes. "When you run barefoot, it forces you to run softer," Yoshino said.

- Yoshino said the majority of the participants enjoyed running barefoot but quit because it wasn't practical.

"I love it. It's very addicting," said Florian Hedwig, one of Yoshino's guinea pigs. "As soon as you take your shoes off, it's a feeling of freedom."

Kevin McCarey, a respected San Diego running coach, thinks walking on the sand barefooted strengthens the feet. He vehemently opposes running barefoot on pavement.

"That is absolutely going to ruin people," he said. "If you were born in America and wore shoes your whole life and now go barefoot, you're going to get every injury known to man."

Ironically, Yoshino worked at a running shoe store for 18 months before recently quitting.

"I wanted to learn about shoes before I complained that they were bad," he said.

His ideal "shoe" is a straw sandal that protects only the forefoot. He runs about 20 miles a week, 10 of them barefoot. He hopes to develop a barefoot community of 50-100 runners.

At last month's Silver Strand Half Marathon in San Diego, Yoshino ran the first six miles barefooted. When the rough pavement began hurting his feet, he pulled his racing flats out from behind his back, laced them up and finished in 1 hour, 20 minutes, 45 seconds, seventh overall, second in his age group.