Sharon Day-Monroe has been to the Olympics twice, in two different events. She's been the U.S. heptathlon champion three times. And she won four consecutive U.S. indoor pentathlon titles.

It's a hugely impressive resume. But at 31, she knows this may be her last shot at Olympic glory.

And that's always a challenge in the pentathlon, which requires an athlete to prove herself over two days in a wide range of skills: speed and strength; power and buoyancy.

"You gotta be able to find the balance for everything," Day-Monroe explained as I spent a recent broiling afternoon with her in Los Angeles.

She was on the track at UCLA, training for the Olympic Trials, which are now underway in Eugene, Ore. She competes on Saturday and Sunday and is considered a favorite to make the U.S. team for the Rio Games, which would be her third consecutive Olympics.

She went to Beijing in 2008 as a high jumper, and followed that with a trip to London in 2012 as a pentathlete, where she finished 16th.

Day-Monroe walked me through the sequence of heptathlon events and what's required for each.

DAY ONE

100-meter hurdles: speed, coordination, balance.

High jump: explosive power, speed, timing, lift.

Shot put: strength and timing.

200 meters: ballistic speed.

DAY TWO

Long jump: speed, power, aerial lift.

Javelin: timing, flexibility, full-body strength.

800 meters: controlled speed and a burst of power when you're exhausted from the other events.

Day-Monroe came to heptathlon in college at UCLA. She was a high jumper and runner, but had never done hurdles or thrown the shot put or javelin.

When a teammate in heptathlon got injured, Day-Monroe was thrown quickly in to replace her. It turned out she was a natural, and coach Jack Hoyt informed her, "You're a heptathlete!"

She's still training with Hoyt, and on the day I watched her he was pushing her through a 400-meter run, followed quickly by two 200-meter runs.

Afterward, Day-Monroe was doubled over, panting, dripping with sweat, and in pain from lactic acid buildup in her hamstrings.

"People refer to it as booty lock," she said, "because everything feels like it's locking up and sometimes cramping. Your muscles are contracting really hard for so long that you can't get enough oxygen in there."

Day-Monroe admits there are times when it seems that putting her body through these seven punishing events borders on insane.

"Especially at the end of the hep or the next day when you just feel like everything hurts," she said, laughing.

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