William R. Watt wrote:

Mostly for hands free operation for taking snapshots or videos.

That makes sense.

But alas, also because upper body muscles put a greater strain on the
heart for the wame amount of power than the lower body. It has something
to do with the upper body muscles being smaller and closer to the heart.

I'm afraid you're baseing your design on a false premise. The small
muscle groups of the upper body are not capable of driving the heart to
as high a rate as the large lower body muscles. I'm also an avid cyclist
and can tell you from experience that paddling is far easier on the
cardiovascular system than cycling is. With the exception of high
intensity paddling while surfing or playing in rocks, I never even get
winded while paddling. By comparison, I can drive my heartrate into the
high 180's on a bike.

It's not even remotely possible to generate the same amount of power
with the upper body muscles as with the lower body muscles, which is why
they cannot drive the heart rate as high. It's also why kayak racers use
boats that allow them to rotate at the hips using the legs to help drive
the boat.

After a heart attack they encourage you to walk and discourage lifting.

That's because straining to lift something increases blood pressure,
especially if you bend over to do it.