You may think dragon boat racing is all about using the arms and shoulders, but the power stems from the legs and body.
It is only at the start of a race that dragon boat paddlers use short, quick strokes that use mostly arm strength to get the boat off to a fast start.
Then paddlers use a longer stroke that leverages the whole body where essentially you are pulling the water. You lean forward, sharply punch your paddle into the water, and then return to an upright position pulling the blade of the paddle against the water. This stroke uses the core muscles of your body (lumbar/abdominal region) and its these muscles that determine your strength and return to an upright position.
As you use your core muscles to sit upright, you also use your legs to push the boat. Have you ever stood on a swing leaned back and used your legs to push the swing to get it going? Although not quite the same, paddlers use their legs to push the boat, and many paddlers have experienced sore legs from training or races.
Dragon boat paddling is also a great cardiovascular/aerobics exercise especially when training.
Because Dragon Boat paddling strengthens your core muscles, many paddlers with back problems have found it beneficial, however always check with your health practitioner.
Here's a general technique video: