To build flexibility and strength, Erin Zeringue regularly practices yoga.

The 39-year-old also loves cruising lakes and rivers on her standup paddleboard, a good workout on its own.

Combining the two seemed like a match made in exercise heaven.

“Both of these are great workouts for stability, so the two together would be great,” she said.

In a pool at the Southside YMCA, Zeringue tried standup paddleboard yoga — SUP yoga as it’s commonly called — for the first time on a cold winter evening along with five other students.

While yoga is about 5,000 years old, SUP yoga has been around about a decade.

The workout places the meditative and stretching discipline of yoga on a 10-foot board. It is meant to deepen the yoga practitioner’s focus and intensify the workout.

“Whether you are a paddleboarder or a yogi, this steps it up a notch in either direction,” said Erin Sullivan, event coordinator for Muddy Water Paddle Co., which coordinated the class.

“You’re stepping out of your comfort zone and trying yoga on the water,” she explained.

Instead of paddling out on a cold, muddy lake, the students worked through the session with their boards anchored by dumbbells sunk to the floor of the YMCA lap pool.

The six students crawled onto their boards, then stood, watching instructor Brandi Hanson lead the movements from the dry concrete.

Hanson directed them to bend from side to side to see how far the board can move without flipping.

“No need to fight it,” she said. “We can still be grounded and centered even if we have movement beneath us.”

Gentle folk music played as Hanson led the class. They started out sitting cross-legged, closing their eyes, then stretched back by lengthening their necks. Then, folding forward, they straightened their legs and touched their toes, each movement causing the board to to move beneath them. Some students found paddleboard yoga easier than expected.

“I like being on water,” said Tracy Yoes, 49, who has practiced yoga for six months and tried SUP yoga on another occasion. “I can do things I couldn’t on land.”

While that notion seems counter-intuitive, Hanson said the constantly moving board helps yoga practitioners meditate more deeply.

“Yoga helps you have complete and total focus,” Hanson said. “You go inward, but you are still physically active. This intensifies that.”

After stretching on the board, Hanson instructed the students to rise into the mountain pose, a strong, standing position for a few breaths. They then leaned down to lengthen their hamstrings before assuming a plank — a horizontal pose with all their weight placed on their hands and feet and their backs as flat as possible to work their midsections.

The class cycled through multiple positions, then moved down to the child’s pose, a compact, prostrate bow.

“That’s a thigh burner!” said Tristan Reid, 22, who had never tried yoga before.

“Especially on a paddleboard,” Hanson added.

When the hourlong class began to wind down, the class rested. Meditating on the board, the students lay on their backs with eyes closed. A few of them absentmindedly ran their fingertips through the water.

“Congratulate yourself for stepping out of your comfort zone,” Hanson told them.

Then Hanson added the traditional parting message of many yoga sessions, the English translation of Sanskrit word “namaste”: “The light in me honors the light in you.”

Out of the water, Reid promised to try the class again. While a strenuous workout, “it was a stress relief.”

“It was almost like there was no gravity at all,” she said.