[pandaman]

>All physical exertion causes pain and discomfort, otherwise it isn't exertion.

Not really, it causes pain and discomfort only when you have fucked up your body to the point where even a small amount of exertion is over the limit. Children seek physical exertion and will do it even against orders. A 6 y.o. is running around not because he is overcoming pain for the future health benefits, he is doing it because it's enjoyable for a body that has not degraded through decades of bad habits. People spend thousands a year on running shoes or bikes or tennis rackets and club membership are not doing that to enhance their pain and suffering either.