Winter's chill - not to mention roads covered in ice and snow - has stopped more than one runner in his tracks.
Triathletes have it even worse.
While the hearty souls always can layer up and hit the road, nobody is swimming Lone Star Lake these days.
So what's a member of the slow-twitch tribe to do when the mercury dives? Suck it up? Cross train? Hibernate until the thaw?
This weekend, at least, the endurance set can lace 'em up without having to batten down.
A short drive to the Kansas City metro area is all it takes to get to three unusual - OK, one of them is unique - indoor events for erstwhile outdoor athletes.
Runners can go up or under, while triathletes need not bother with the ice breaker or drysuit.
Here's a look at the three opportunities for endurance athletes to get their race on:
Vertical Dash for Diabetes
The Vertical Dash for Diabetes has Saturday to itself on the running calendar.
A benefit for the Kansas City chapter of the American Diabetes Association, the Dash is a race up 34 floors of the Town Pavilion Building in downtown Kansas City, Mo.
"It's like nothing most people have ever done before," race director Courtney Lorenz said. "The fastest time last year was 4 minutes, 17 seconds, and we had somebody who walked it in 20 minutes, so it can take anywhere from four to 20 minutes."
Runners can skip stairs and use the handrails.
"However you can get to the top the fastest," Lorenz said. "Actually, some people trained just for this."
The Dash is in its second year.
Lorenz said the event - with kcfit.net as host - came about when a kcfit.net owner did a similar race in Chicago.
There are hundreds of stair races around the world. The longest in the United States is the 103-flight Go Vertical Chicago, up the Sears Tower.
Though the Kansas City version lacks the altitude, it has much the same vibe.
"We tried to find the tallest building in Kansas City. Town Pavilion is the second tallest, and they've been very generous in helping us put it together," Lorenz said. "They provide the security, the location, let us use the stairwell : they've been great through it all."
Last year's event, won by former Oklahoma State runner Derek Tate, drew 54 people and raised close to $2,000. By midweek, Lowrenz already had 70 signed up for this year's race and hopes to draw close to 100, raising close to $5,000.
"I think the overall reaction is, 'Wow, that's not what I expected,'" Lorenz said. "It's a lot harder than most people think. But it's a great rush, a great accomplishment. Hopefully, as the years go by it will continue to grow."
The Sylvester Powell, Jr. Community Center in Mission will be the site of an unusual indoor triathlon Sunday.
Competitors in the first-time event will swim 10 minutes in a 23-yard lap pool, ride 30 minutes on a spin bike and run 20 minutes on a treadmill. Winners will be determined by cumulative distance.
"Somebody else has done this before," said program supervisor Scott Deschenes. "I found it on the Internet. We have a lot of people who are triathletes who come to the center, and I've been trying to do more programming for them. I thought it would be cool."
Deschenes thought he'd limit participation to the first 42 to sign up. He filled those slots by Sunday, and registration didn't close until Thursday.
"I am, actually, kind of surprised," he said. "It was a big leap in faith."
Deschenes admits the format could be tweaked in the future. As it is, it tends to favor cyclists.
"We might do a point system in the future," he said. "We're learning as we go. : But there's definitely a lot of interest. We've talked to a local triathlon group about joint programming. We have the pool, the spin bikes, the treadmills and a track. We might do something together in the future."
While the indoor triathlon and Vertical Dash are relative newcomers to the endurance scene, the Groundhog Run is not.
Held completely underground at the Hunt Midwest Subtropolis in Kansas City, Mo., the event will be held Sunday for the 26th straight year.
"The other races are separate and unique in their own way," said Jerry Morrison, race director for all but the first year, "but everybody comes to the Groundhog."
The event - believed to be the only 5K/10K race in the world run completely underground - is capped at 3,250 runners.
At the registration-cutoff point Tuesday, close to 3,000 had signed up, Morrison said.
What's the allure?
"At this time of year? It's inside," Morrison said. "It's 58 degrees. It's inside all the way. It's flat. There are no hills. And it sort of kicks off the running season, at least here. It's the first major race in Kansas City. That's why it's unique. I get calls from all around the country: 'Is it really underground?' Yes, it's really underground. There are bats."
OK, he's kidding about the bats.
But runners really don't see the light of day during their one (for the 5K race) or two (for the 10K) loops through the world's largest underground business complex.
The event, ranked as one of the top 65 runs in the country by Runner's World magazine, is a benefit for the Children's Therapeutic Learning Center.
"It's not a record-setting course," Morrison said. "There are too many turns. There are twists and turns around the pillars. There are no championship times. Basically, it's a good run, and you can go fairly quick."
And, unlike most other runs this time of year, you stay warm doing it.