AMHERST, Mass. — Swimming wasn’t always one of Sydne Didier’s favorite activities. As a child, she admits feigning ailments to get out of swimming lessons. It wasn’t until she was 26 that she learned her first swimming strokes in a class for beginners while studying at Portland State University.

Seventeen years later, Didier, 43, can’t seem to stay out of the water. She is not only a private swimming coach and instructor but competes in long-distance, open-water swimming races, in locales ranging from the Caribbean to the Jersey shore to the Swiss Alps.

On Aug. 10, Didier, of Amherst, took second place in the women’s 40 years and over masters bracket at the Lake Zurich Marathon Swim in Switzerland, a 26.4-kilometer race (16.4 miles) across the famous lake from Rapperswil to Zurich. She was the only swimmer from the western hemisphere in the race, which draws mostly Europeans. She was flanked by two English women in the standings.

“Every swim puts you to the test,” said the battle-tested Didier in an interview recently in her backyard, which is home to a 25-yard indoor lap pool.

Didier finished the Lake Zurich swim in nine hours, 10 minutes and 52 seconds, and there were plenty of things that put her to the test. Competing with jet lag in her longest race to date, she also had to contend with major left shoulder pain that set in about five hours into the race, testing her physically and mentally.

“There was a point where I thought my shoulder wasn’t going to let me finish,” recalled Didier, who says she willed her way to the finish line. “There’s always a point where you think, ‘This is so stupid, why am I doing this?’ Every race, that (thought) comes.”

But for Didier, long-distance, open-water swimming – a sport she began to specialize in after competing in triathlons in the late 90s – is a team sport.

Nearby in a kayak throughout the race were her husband, John Urschel, and 13-year-old son, Aiden, keeping tabs on Didier from her support boat. The pair helped Didier with feedings along the way, 8-ounce liquid fuel bottles, including Gatorade. They monitored her swimming strokes and nutrition and looked for signs of anything out of the ordinary from late-blooming long-distance swimmer who was competing in water at roughly 70 degrees.

“From a kayaker’s perspective, it’s incredibly quiet,” Urschel said of the back-and-forth he has with his wife while she’s swimming. “It’s more physical cues.”

Having been at her side while she competed before, including in a race with six-foot swells and a small craft advisory off the New Jersey shore last September, Urschel said he never doubted Didier would finish the Swiss contest, despite her intense shoulder pain. “She does not give up,” he said. “If she starts something, she finishes it.”

Writing about her experience in a blog post about the race, Didier said it was mind over matter that helped her get through. She began to envision herself at the finish line and thought about how she’d feel to come all that way and not finish – and to have to share that with her family, friends and swimming community back home. She even worried about her husband and son in the kayak, given that her swim was more than nine hours long.

“That’s a long time to do anything,” Didier said.

She said she has never been interested in swimming indoor pool races largely because of the intensity of the competition. Rather, she developed a passion for open-water swimming, a sport that gets far less attention and one in which swimmers, “swim for themselves,” as her husband put it.