Tischa Yates plans to do things for the first time on back-to-back days that lots of people think are crazy.

Yates will run the Honolulu Marathon on Sunday. On Monday, she will skydive.

Yates, 40, is a mother of four from Lake Stevens, Wash., who doesn’t consider herself an athlete.

“I played soccer in middle school, but I don’t know if that counts,” said Yates, when asked about her running background. “My best friend, Jamie Wilson, ran a marathon, and it’s all she would talk about, so I decided I’d try it.”

Yates started training 18 months ago. She chose Honolulu for a couple of reasons.

“First off, there’s no time limit,” she said yesterday, after picking up her race packet at the Honolulu Marathon Expo at the Hawaii Convention Center. “No. 2, the trip to Hawaii makes it worth training for.”

Her husband, Jon, came up with Monday’s part of the adventure since he has skydived before. They and two other family members will also do the Kalakaua Merrie Mile on Saturday.

Chad Leitermann, 27, is another first-time Honolulu Marathon entrant. He came by himself from his home in Tempe, Ariz., but has already made new friends at The Beach Waikiki Hostel.

“Me and my three roommates are all shooting for sub-four (hours),” he said. “The hostel experience is great. It’s more geared for people in their 20s and 30s.”

These are among the many thousands coming through the expo, which started Thursday morning and ends Saturday. Runners pick up their number bibs, and peruse the wares of dozens of vendors selling everything from beauty products to vacation packages — and many other items more closely associated with distance running, like shoes and workout gear.

More than 35,000 people — some local, others from all over the world — are registered for Sunday’s marathon or Start to Park 10K, and/or Saturday’s Kalakaua Merrie Mile. Some are still registering late, at the expo.

Around 400 signed up Thursday, many waiting when the doors opened at 10 a.m.

“It was pretty crazy,” Honolulu Marathon spokesman Fredrik Bjurenvall said.

It’s part of a new running boom, and 40% of Honolulu’s entrants are first-timers, Bjurenvall said. It’s not just here. Marathons in New York, Chicago and other large cities have experienced record registration numbers, too.

“(The boom) has nothing to do with the top performers, which to me means it will be more enduring,” Honolulu Marathon president Jim Barahal said.

Steve Davidson, 78, has run Honolulu more times than he can remember. He is the secretary of the Mid-Pacific Road Runners Club. MPRRC was established in 1962 and organizes more than 20 races per year.

“I would say our membership has been stable,” Davidson said. “What we are seeing now is new running groups that do a lot of things together in addition to running.”

Michael and Pauline Garrison of Hawaii Running Lab have noticed the boom, too.

Michael Garrison earned a Ph.D. in kinesiology and was a successful college distance running coach at Arkansas, Maryland and the University of Hawaii. He now coaches individuals — some face-to-face in Hawaii, others all over the world via technology. He said he never thought he’d design and sell running apparel, too. The shirts and other clothing items at the Hawaii Running Lab kiosk are among the most eye-catching at the expo.

“A lot of it now is about the kit,” Barahal said.

Like the actual events, the expo could not succeed without volunteers. Honolulu Marathon office manager Val Lawson supervises 14 from Japan, and around 200 others, mostly from Oahu.

Ed Narimasu is in his 21st year as a volunteer. The retired shipyard mechanical engineer worked on registering Start to Park 10K entrants Thursday.

“We got run over this morning,” Narimasu said of the early rush when the doors opened at 10 a.m.

He was a marathoner himself, inspired by watching his brother, Wayne, cross the finish line in 1976.

“I saw the old ladies and fat men finishing before him, so I trained and did it the next year,” Narimasu said. “I ran it a few more times and I noticed all of the volunteers. I told myself then that when I retired I’d volunteer, too,”

A young man from Chicago who was then a Navy diver volunteered with the Honolulu Marathon cleanup crew in the 1970s. A young local woman running her first marathon was told by a mutual friend that the runners were supposed to help with cleanup. That fib is how Smiley and Val, who eventually became Mr. and Mrs. Lawson, met.

They both worked at the Honolulu Marathon Expo on Thursday, nearly five decades later.