To prepare for this article, I Googled terms like "bonding and exercise," "heart rate and friendship," "fitness and relationships."

I didn't find much.

Can it really be that researchers haven't studied whether two people exercising together bond more quickly than people doing other activities? It seems like a no-brainer to me. We've all read stories about heart rate and attraction—how a person's heart rate and energy level increase when he's attracted to someone, which in turn increases his alertness and interest. We've also heard about people bonding through experiencing a mutual challenge.

Seems to me these states apply to people who exercise together. Heart rates and energy levels increase during exercise, and I can't remember the last workout that wasn't a challenge. If I'm exercising in tandem, why wouldn't these physiological and psychological effects encourage increased friend bonding, as they do in other pair bonding?

Lack of scientific research aside, I believe they do. (As I've written before, getting me moving is the best way to connect with me.)

I've made some incredible friendships through exercise.

Certainly, it's partially because exercising is how I spend a lot of my "free" time—and people always make friends during playtime. But the nature of the playtime has to make a difference, even if only a small one.

Here’s my thinking:

• While sweating and struggling, you can't get away with too many airs or false pretenses. Exercise reduces you to your core elements. I've seen people who otherwise might be intimidating or high-falutin' on their knees in the gym or crying through a long run. I like long-distance relay races, and after two days in a van with a group of people who haven't eaten a solid meal, showered (unless you count baby-wipe baths), or slept, you can truly say you've seen them at the base of Maslow's hierarchy.

• You'll learn a lot about someone when you see him face a challenge. You may learn good things and you may learn bad things. Either way, you'll more quickly than otherwise grasp whether this person is worthy of your time and effort. Getting to know someone through exercise helps prevent friendships in which only later you realize someone's a jerk.

• When you get to know people through exercise, you might very well be there for some pretty special moments in their lives. And even if you're not training together toward a breakthrough, you'll push and support each other. Going through something with someone—especially on a regular basis—makes for some pretty powerful friendships.

• Do anything often with someone, and you'll get to know her pretty well. Distance running is especially well set up for this. A two-hour long run with a stranger? She won't be a stranger long. Before you know it, you'll be each other's counselors and trusted advisors on things political, corporate, and personal. One of my closest friends today was a business acquaintance who became a friend only after we'd sweated through a few runs together, when I'd confided in him about a personal-life challenge, and he'd shared a trauma he'd experienced at his then employer. Running aside, I've also forged friendships in the gym over regular half-hour lifting sessions. Even when you're chuffing air and streaming sweat, you have a lot of time for talking and sharing.

Yesterday I went for a run and saw three people along the route that I knew well. Many times I've gone out for some exercise and found a new friend. I'm going to keep at it. We all have a rare few people for whom we'd go the distance. Many of mine I've met through exercise.