Endurance sports naturally command a shred of masochism and attract those "strange" people who take pleasure in the pain of taxing their bodies and pushing the limits. Let's face it, we are those strange people, fundamentally different from our siblings and co-workers, or the guy sitting next to you on the train.

We are swimmers, runners, cyclists and/or triathletes who seek out various events to test ourselves, and gladly assume the pain that is part of the sports that we love. From a 5K to an Ironman, any event might be considered a "grueling" one, but here is a short-list (in no particular order) of some of the most grueling events in Chicago, should find yourself wondering just how far you are willing to go.

1. The LaSalle Bank Chicago Marathon.
If 40,000 people register for it each year it mustn't be too grueling, right? Wrong. It's still a 26.2-mile race, and 26.2 miles is a long way to run no matter who you are. From the elite athletes who cover the distance in just over two hours, to those who cross the finish line more than four hours later, it's a painful race. Take into account the swirling wind, oftentimes chilly fall temperatures, and the fact that 40,000 people are corralled onto a 40-foot wide road, and the marathon becomes more than just a long run, but a war against the weather, the other competitors, and most importantly, yourself.

2. Go Vertical Chicago Stair Climb.
Elevators were invented for good reason, especially when you're trying to reach the top of what was once the tallest building in the world. Still the highest skyscraper in the U.S., this event has participants hoofing their way to the Sears Tower Skydeck. That's 103 floors, or 2,109 steps. Talk about a quad killer, this event amounts to more than an hour of straight climbing for many people, although some of the top stair- climbers in the country conquer it in less than 14 minutes. Either way, you'll appreciate the fact that while your own two feet got you to the top, an elevator will take you back down.

3. Flatwater Classic Paddle.
You can approach this event in one of two ways: a leisurely paddle down the Chicago River, admiring the architecture along the way, or an all-out flurry to the finish with paddles churning and forearms and lungs afire. Obviously to be on this list, consider the latter. The 7.25-mile route from the city's Northside to Chinatown can take anywhere from an hour and a half to more than three hours of good, hard paddling. And if you've never tried it, paddling is a full body sport; everything from your fingertips to your toes will be sore the next day.

4. Big Shoulders Open Water Swim.
Five kilometers is a very popular running distance, but a swim? Forget it. And not just any swim, an open water swim in wind-swept Lake Michigan with water temperatures anywhere from 64 to 73 degrees. You've gotta have big shoulders for that. The swim classic starts at Ohio Street Beach and follows a 2.5K loop done twice, taking even the most accomplished men and women well over an hour to cover the 3.1 miles of choppy water. Additionally, there are two competitive categories: wetsuit and non-wetsuit. Guess which category gets the nod on this list? That's right, grueling means sans wetsuit.

5. Chicago Lakefront 50/50.
The first 50 means 50K (or 31 miles), and the second means 50 miles. Both these distances are worthy of the list. An ultra marathon means anything longer than a standard marathon, but this event is ultra tough for several reasons. Staged on the Chicago lakefront, the 50/50 course may be flat, but it's subject to wind, wind, and more wind, which has become part of the event's challenge and even part of the appeal for those brave enough. But the kicker is that the course runs several times out-and-back, meaning you have to bypass the start/finish area on more than one occasion before looping back out for more miles. That's the definition of grueling.

Check Chicago Athlete's event calendar for more information on these and other events.