So what does it take to be a competitive surfer? Besides a board and some cooperative water, you’ll need endurance, strong paddling muscles, and the ability to respond quickly.

Those are the conclusions of a first-of-its-kind study on the physical demands of surfing, which was recently published in The Journal of Strength and Conditioning Research.

Researchers outfitted 12 professional surfers with GPS units and heart rate monitors and then tracked them in competition.

During the 20-minute heat, surfers spent more than half their time paddling, 28 percent of their time waiting for waves, and just eight percent of their time riding waves, while covering a total distance of about a mile.

That sounds dull until you learn that more than 60 percent of the time spent paddling or waiting for waves lasted less than 10 seconds. So most of the time athletes were responding to rapidly shifting conditions.

The average heart rate was 139 beats-per-minute with a peak rate of 190 bpm. Heart rates for all competitors remained in the moderate- to high-range during the contest.

And there was ample reason for those elevated heart rates. While the average speed on a wave was 20.75 mph (with one lucky surfer clocking a top speed of nearly 30 mph), surfers traveled at an average speed of 2.3 mph in the water.

Researchers expected heart rates would be highest when surfers were paddling. But, as anyone who’s surfed could tell you, heart rates soared most when riding waves.

“One reason for such a result could be the physical demands of riding the wave, coupled with the adrenaline release ensuing from the wave ride and fall,” wrote study leader Oliver Farley of New Zealand’s Auckland University of Technology.

You only have to ride one wave to know that’s the least surprising finding of this study.