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NEW YORK (Reuters) - small paddle board has surged to a fast-growing water sport that fitness experts say delivers a full-body workout to anyone exercising on an ocean, lake or river.

About 1.2 million people tried mini stand up paddle board in 2011, up 18 percent from 2010, according to the Outdoor Industry Association’s 2012 report, and nearly 60 percent of SUP enthusiasts tried it for the first time in 2011.

SUP is said to have started when surfing instructors in Hawaii stood up on their boards to photograph their clients. It involves standing on a long board and using a single paddle to propel through the water.

“It’s accessible to just about anyone with any athletic inclination,” said Will Taylor, associate editor of SUP Magazine. “Even my grandmother would be able to paddle around on flat water.”

SUP boards are larger and much more stable than standard surf boards, Taylor said.

“If you’re older, you can basically take a stroll on the water: paddle slowly, take in sights,” he explained. “If you’re a marathoner, you can paddle really hard or do intervals.”

Taylor said just standing on the unstable platform engages the stabilizer muscles, while paddling targets the upper body.

“This is a little more full body than surfing because you’re standing the whole time,” he explained. “It’s a balancing act. The core is really getting worked.”

Carey Bond, an instructor and guide at Manhattan Kayak Company in New York City, co-founded the Suplogix research group to explore the biomechanics of small inflatable paddle board.

“The health and fitness benefits are proving to be quite significant,” said Bond, whose company uses biotechnology to measure muscle activation during SUP.

“All of your stabilizing muscles in hip, lower leg, knee joint are activated in a therapeutic way to stabilize balance on the unstable surface,” he said.

The intensity of the workout also depends on the body of water, according to Dr. Cedric Bryant, chief science officer for the American Council on Exercise.