PORTLAND — From the bleachers by the pool, Cheryl Brackett watched athletes swim laps and receive instruction at a workshop Sunday for aspiring triathlon competitors.

Brackett, 45, is registered for the Tri for a Cure race in South Portland on Aug. 15, which calls for a one-third-mile swim in Casco Bay, a 15-mile bike ride and a three-mile run.

Brackett runs regularly and does some biking, but swimming is another story. She began learning how to swim in November.

“Being a first-time triathlete, and I use that term loosely, I’m looking for all the knowledge I can get,” Brackett said. “I began taking private lessons to maybe learn to swim better than a doggie paddle. I was informed I’m a sinker. I’m a work in progress.”

Brackett was one of 45 people who attended the daylong clinic, sponsored by the city of Portland and Tri-Maine, at the Riverton Community Center Pool.

Competitors had a chance to learn skills, get some pool time and share information with other triathletes.

There was a running seminar, a bike-fit clinic and transition demonstrations.

Swimmers received an analysis of their strokes from an underwater video camera, then instructors offered tips for improving their techniques.

Participants asked what to do in the transition from swimming to biking and what types of clothing they should wear.

Nicole Pisani, race director for Tri-Maine, offered advice for finding the right bike seat. She said it took her a few seats before finding the right fit.

“I remember my first few rides and how painful it was,” Pisani said. “Eventually, you will toughen up there. A padded pair of bike shorts will help.”

Triathlons have grown in popularity in recent years, with interest rising among women.

The Tri for a Cure race for women filled its 800 spots in record time. That race also offers clinics for athletes.

Pisani said roughly 75 percent of the participants in Sunday’s clinic were women.

Among them was Laura Heckman of Windham, who is participating in the all-women SheRox Webster triathlon in July in Massachusetts.

It will be her first triathlon, and she said the clinic helped her prepare and know what to expect.

“I feel like I have a better understanding now,” Heckman said. “It will be a big accomplishment. I can’t wait to cross the finish line.”

Kate Anderson of Windham convinced Heckman to sign up for the SheRox triathlon, which they are doing together. Anderson said she decided to register because she needed a goal to help her exercise consistently. She said she found the clinic’s information about transitions and tips on cross-training to avoid injuries very helpful.

“Every day, I get more and more excited,” Anderson said. “If someone told me two months ago that I’d be able to run two miles without stopping, I would have laughed. I did that Saturday. It felt great.”