Exercise needn’t be painful — even for people with arthritis.

Doing workouts while partly immersed in water, according to the Arthritis Foundation, can help relieve pressure on stiff joints and provide new freedom of movement. So much so that participants sometimes forget themselves.

“We do no more than eight repetitions” of an exercise, said Heather Harris, who teaches a Montgomery Village, Md., class in the Arthritis Foundation Aquatic Program.

Participants feel “so good in the water,” she said, that “they don’t (always) realize when they might be overdoing it.”

Water exercise classes aim to maintain or increase participants’ range of motion — a key goal.

“The pain is so high (for many arthritis patients) that they don’t want to move,” said physiologist Calaneet Balas, president of the Metro Washington Chapter of the Arthritis Foundation.

But immobility “only perpetuates the problem,” she said. Without exercise, “you’re going to get weaker.”