This article originally appeared in the July/August 2016 issue of SELF.

This full issue is available June 28 on national newsstands.

I surged forward, cursing myself for sticking to pancake-flat pavement during my three months of training.

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The other runners around me seemed equally daunted: I could hear groans as some of them dropped off.

As tightness invaded my pumping legs and arms, I fought the desire to let up.

My mind scanned for somethinganythingtomotivate me.

The thought hit me: Karly.

If only she were there, wordlessly urging me to keep pace.

Karly was my running twin.

We ran together on the high school track team, sharing sweaty hugs after grueling 800-meter dashes.

We had similar body typesshort, with thick, muscular legsbut it went beyond that.

Our personal racing records were nearly identical, too.

Recruited toruntrack at the same college, we decided to become roommates as well as teammates.

By the end of freshman year, she was one of my best friends.

On weekends, we lounged around in matching team sweats, reveling in Beyonce and the Green Bay Packers.

On Halloween, she was Baby Spice to my Sporty.

We shared terrible postmeet hot wings and inside jokes about cute guys.

Still, there was no mistaking her competitive streak.

Anytime we ran, she’d have a go at beat me.

“I’m not going to sprint,” she’d swear before a training run.

Then, inevitably, halfway through, she’d get fired up.

I’d take a deep breath and follow.

When she moves, you move," as I nodded and mentally fixed a target to her back.

It was the exact same thing he’d say to her when I won.

Karly was there to witness my victory whenever I managed to edge her out.

It had always been this way in our friendship.

But as college went on, the stakes got much higher.

Running a 56-second 400-meter dash meant you had the chance to be an all-American.

My brain seemed stuck in slow motion; my muscles were like bricks.

She had just run a national-meet-qualifying time.

I had run one of my best times of the season, but it didn’t matter.

Next to her, I felt invisible.

And yet we did everything we could to avoid any awkwardness.

Because we were friends.

On the field, we were constantly fighting to occupy the same space.

Sometimes the tension encouraged me: I knew her race times were within my reach, attainable.

But that same tension crushed me anytime she beat me.

If only I’d pushed a little harder, finished stronger, been more strategic.

I had put in the work.

The prize wasthis close.

But it was snatched away in a blinkand I felt the ache.

For so long, I was good at hiding it: putting on a smile, being supportive.

Eventually, I just wasn’t anymore.

I was burned out from all the pressure, and it showed in little ways.

I’d feel a twinge of annoyance when she’d up the pace in practice.

(Why did she have to make me look bad?)

I’d waffle between relief and guilt when she mentioned an injury flaring up.

As the months went by, the emotional distance between us grew.

“You should come with us,” she’d offer.

“I just really need to study,” I’d say, waving her off.

By spring, I’d let someone else take the seat next to her on the team bus.

She’d leave the locker room without waiting for me.

I threw myself into my classes and internships, arenas in which I could excel.

Without realizing it, I was collecting and nurturing the things that made us different.

We never talked about it.

I knew I’d miss her friendship, but I was relieved to say good-bye to the competition.

As it turns out, I miss both.

After my first half-marathon I looked up Karly’s time.

Karly and I still keep in touch now and then.

Every few months we catch up via text.

I play it out in my head, us sprinting to the finish.

I end up not asking.

I do know that she ran her firsthalf-marathonright out of college with some of our former teammates.

But then I told myself that competitive running wasn’t really my thing anymore.

It rang true enough, for a time.

It’s hard to find a friend who’s comfortable making you uncomfortable.

Whether they’re behind you or ahead of you, they expand your sense of what’s possible.

I finished the race.

I braced myself as I clicked the link, waiting for her name to pop up on my screen.

Would I feel like a loser if she’d blown me away?

Or was I the winner of a race nobody knew about but me?

I stared, dumbfounded.

What were the chances?

And I kind of couldn’t wait to tell her.

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