novice wrote:
I have good cardio from running/biking but I have never really been out
of breath while kayaking. I'm doing a bout 8.5 minute kilometers in 10
ft by 28 inch wide kayak.

Try out your cardio by running on your hands or biking with your arms.
See how long they last then.

Your have smaller muscles than your legs; they don't need to work as
hard to get tired, and don't use as much oxygen, so you won't get much
of a cardio workout from your arms.

Good kayaking technique will utilize the torso muscles more than the
arms. You should feel your abs burn before your arms -- if you do, you
will get a better cardio workout. Maybe ask some sprint racers? Or just
take some sea kayaking lessons.

Andrew