In an effective paddle stroke, the bottom arm (the one nearest the water), a bit like the top arm, hardly changes shape. At the start of the stroke, your bottom arm should be extended, almost but not quite straight out in front of you. The stroke starts as far forward as you can reach by rotating your torso and keeping your arm straight. The paddle enters the water as close to the boat as possible but then follows a path out and away from the boat.

The purpose of the bottom arm during the power phase of the stroke is to guide the paddle and to transfer power from your legs and torso into the blade. To achieve this, the arm should stay almost straight during the time the blade is in the water which will result in the paddle being swept out and away from the boat. This will ensure that you are using your whole body to move the paddle and not your arm to pull which is inefficient and very tiring. Also if you pull the paddle with your arm, the paddle will move past vertical (as seen from the side) very quickly resulting in a lot of wasted effort as you start to lift water.

Have a look at Ed McKeever’s lower arm in the photos below: it is straight at the start of the stroke and has remained almost straight right until the end of the stroke. Also note how the paddle sweeps laterally away from the boat. You only bend the lower arm when you take the paddle out of the water, getting ready for the next stroke.