AP Photo/David J. Phillip

Two weeks from her 39th birthday, Therese Alshammar was in the pool at the Rio Games representing Sweden at the Olympics for the sixth time. She is the first female swimmer to achieve that feat, though sometimes she wonders how her body keeps going. 

"How old do I feel? It varies from day to day, I have to say," Alshammar said. "Some days I feel like I'm way past my age and some days I feel younger."

Alshammar dealt with a back injury over the winter that hampered her preparation, but gradually worked her way back into shape for one more run. She has three Olympic medals to her name and led the Swedish delegation into the arena for the opening ceremony.

She finished her 50-meter freestyle preliminary heat on Friday afternoon in 24.73 seconds. It was the 12th-fastest time in the field and allowed her to advance to the semifinals on Friday night.

Alshammar first competed in Atlanta in 1996. To put that in perspective, 16-year-old Canadian star Penny Oleksiak wasn't even born until 2000.

With young faces all around her, Alshammar said she never could have imagined remaining at the highest level for so long.

"Never ever," she said with a chuckle. "When I was in my first Olympics I remember thinking, 'This is probably it.' Six later, and I'm still here."