"Only one other animal on the planet wears shoes, and only because we grab them by the legs and hammer them on." -- Christopher McDougall, author of the national bestseller "Born to Run"

Scott Hadley’s introduction to barefoot running mostly was accidental.

As a sophomore in college in 1989, he fractured his hip playing soccer. After a series of surgeries, doctors determined the injury likely kept one of his legs from growing, leaving him with a one-inch difference in the length of his legs.

About 15 years later, Hadley tried to take up running, but constant pain limited his workouts to a couple of miles at most. At that point, though, he had doctorates in anatomy and physical therapy, and he used a therapy technique that was so effective on other runners that he decided to try it.

MERRELL NAKED FOOT 5K

When:

9 a.m. Sunday

Where:

Riverside Park, Grand Rapids

Cost:

$35 in advance; $40 day of race

Free kids fun run:

8:30 a.m.

Website:

As he went into a modified hamstring stretch one night, something in his lower body cracked and, when he stood up, his legs suddenly were the same length. He now figures his legs always were the same, but the injury jarred his pelvis out of alignment.

Nonetheless, after more than a decade of wearing one-inch lifts to compensate for the difference, Hadley didn’t wear any shoes for the next four days. One afternoon, he started to run around with his kids at a park and realized he wasn’t feeling any discomfort.

"It was the most extraordinary experience I’d had in a long time," the 40-year-old Grand Rapids resident said. "That was the first time I had run without pain in 15 years."

In large part, he credits the shift to going barefoot.

Barefoot running isn’t exactly a new trend, but an increasing number of people are foregoing traditional shoes for either their bare feet or minimalist shoes, which are made out of lightweight, flexible materials and provide limited support and only minimal protection for the bottom of the foot.

Barefoot running, common in nations where shoes might be considered a luxury, has gained attention in recent years. Some studies claim it can prevent injuries, improve form and correct biomechanical issues that lead to lower body pain and other ailments.

Opponents say there’s not enough research to back up those claims, and many new barefoot runners are injured because they rush into it without knowing the proper form or technique.

All Hadley knows is that it works for him. Even though his legs were the same length, he wasn’t comfortable running in shoes. Two years ago, he ran the Fifth Third River Bank Run 25K barefoot.

"It was really because I couldn’t run without pain in shoes," Hadley said. "I had orthotics, I had surgery on my knee, I had the best motion control shoes I could possibly find because I have really flat feet, and none of it was helping until I started running barefoot."

"Shoes do no more for the foot than a hat does for the brain." -- Dr. Mercer Rang, noted orthopedic surgeon and researcher in pediatric development

The first obstacle many new barefoot runners face is the fear each workout will be accompanied by the removal of glass, gravel, sticks and other sharp objects from the bottoms of their feet.

That’s what Jared Behrens of Grand Rapids thought when he took up barefoot running about six months ago.

"I had to overcome that quite at bit at first," the 28-year-old property manager said. "But I kind of like the adventure of trying something new, so to me it was a challenge. It sounded kind of extreme, and that’s what got me into it. I was slightly disappointed because, when I started, I realized it really wasn’t that extreme.

"Your feet are very sensitive, and because of that you’re scanning the ground, making sure you’re not stepping on any glass shards or anything like that."

In fact, barefoot running requires a lot more than attention to surroundings. Proper form is a must.

Instead of landing on the heel, runners have to use the forefront of their foot. They take shorter strides, which is intended to keep the foot directly below their center of gravity. And they use softer steps, which allows the leg to act as a shock absorber instead of a brace.

As a result, many runners find that nagging knee and foot pain that had bothered them before starts to dissipate.

They also use different muscles than they would with normal shoes, especially in the calves and feet.

Behrens said it felt like someone had taken a baseball bat to his calves after his first 2-mile barefoot run.

"It was a little tough. The body takes some adjusting with the whole barefoot running thing," Behrens said.

Grand Rapids’ Kerri Delacher, race director for Saturday’s Merrell Naked Foot 5K, said she used to experience knee problems after competing in triathlons and marathons. But she started to incorporate barefoot running into some of her workouts — she still uses normal running shoes, too -- and the pain disappeared.

"With any kind of regular running shoes, as long as you have the correct form, you’re going to eliminate injuries," said Delacher, 37. "But running barefoot, I’ve noticed, forces you to correct those bad running forms that you might have had all your life."

Hadley agreed that form is important. That’s why he regularly holds barefoot workshops at his Grand Rapids physical therapy clinic at 1140 Monroe Ave. NW.

"From what I can tell, a lot of people are trying barefoot running in an uneducated way and getting injured," Hadley said. "I made it a part of my physical therapy practice to teach people how to run properly barefoot."

"Like the rest of our bodies, the foot is designed to run. Simplicity is key. A shoe shouldn't be a La-Z-Boy recliner." -- former Boston Marathon and River Bank Run champion Bill Rodgers

Grand Rapids is one of only seven cities in the nation hosting one of the Merrell-sponsored barefoot 5Ks, which also raises awareness for Soles4Souls, a Nashville-based charity that collects and delivers shoes to people in need.

Delacher said Sunday’s event is designed to introduce people to barefoot running, but participants who want to keep their traditional shoes are encouraged to attend as well.

"Our motto is, ‘It’s not about the barefoot movement, it’s about the movement movement,’ " Delacher said. "We want people to come out for a fun event, try something new. People with regular running shoes -- we call them shod runners — are totally welcome. If people are curious about barefoot running, then that’s great. But our focus is getting people off the couch and doing something healthy.

"We don’t discriminate."

The barefoot and minimalist movements are gaining steam -- virtually every major shoe company, from Adidas and Nike to New Balance and Saucony, carries a minimalist line -- but Behrens said he understands why he still gets odd looks and questions from strangers when he runs barefoot at local events.

"When I stepped into it, it was pretty foreign to me also. That’s when I realized how many people were actually into it," Behrens said. "I thought it was just some crazy, hippy thing that was going on, but then I got into it and saw that this was a really large group of people."

Hadley said barefoot running doesn’t exactly qualify as a fad, but he expects as more people learn about the science and reasoning behind the trend, more will be encouraged to take up running.

"I think a lot of people think barefoot runners perceive themselves as tough or holier than thou or whatever, and maybe some might have that attitude," Hadley said. "But people like me, who do it because it’s the only way we can run, we actually have a very humble opinion of ourselves.

"I actually wish I was strong enough person to run in shoes. My body just doesn’t allow me to do that very well."

E-mail Michael Zuidema: mzuidema@grpress.com and follow him on Twitter at twitter.com/michaelzuidema